Further Studies on the Action of Prolactin on Fluid and Ion Absorption by the Rat Jejunum JAMES R. MAINOYA Department of Zoology and Cancer Research Laboratory, University of California, Berkeley, California 94720 ABSTRACT. The influence of administration of ovine prolactin in vivo on intestinal fluid and ion transport in vitro was investigated using intact and hypophysectomized male rats. Prolactin administration significantly stimulated fluid, sodium, potassium, calcium, magnesium and chloride transport across everted jejunal sacs. The last two ions were affected less than the others. Hypophysectomy caused a significant decrease in fluid and sodium absorption, but prolactin treatment for 2 days restored normal absorption rates but not uniformly in all sacs. Prolactin action on fluid and sodium absorption showed a dose-dependent tendency, maximal stimulation resulting from administration of 1.0 to 2.0 mg prolactin daily; higher doses failed to elicit significant response. The stimulatory action
of prolactin was inhibited by a simultaneous administration of vasopressin which when given alone had no effect on intestinal absorption. In the absence of glucose or in the presence of phlorizin, fluid transport was inhibited, the reduction being more dramatic in the presence of phlorizin. Similarly, either application of ouabain or partial replacement of sodium with isotonic choline chloride reduced fluid transport. Although these in vitro treatments nullified the stimulatory effects of prolactin, only phlorizin and ouabain significantly decreased sodium transport. These results suggest that the effects of prolactin on intestinal transport may be dependent on increased movement of sodium. (Endocrinology 96: 1158, 1975)
AMONG the many and diverse actions -t\. of prolactin in the vertebrates (1,2). an important contribution to osmoregulation has been demonstrated in teleost fish (3,4) and indicated in other nonmammalian vertebrates. Assessment of the role of prolactin in hydromineral metabolism in mammals has been based mainly on two experimental results: either the increased ability of the prolactin-treated animal to retain water, sodium and potassium (5,6) or changes in plasma prolactin levels in response to osmotic challenges (7,8). Ensoref al. (9) reported that in female rats dehydration was associated with a decrease in pituitary prolactin levels and suggested that prolactin might stimulate increased fluid intake especially during lactation. Much evidence indicates that certain hormonal states may influence intestinal absorption of water and solutes (10,11); however, reports on the effects of adenohypophysial hormones on intestinal absorption are scarce. Although it has been demonstrated that prolactin administration
significantly stimulated fluid absorption by the rat small intestine (12,13), little is known of the action of prolactin on intestinal absorption of ions. The present experiments were designed to investigate the effects of prolactin on fluid and ion absorption by the rat jejunum.
Received June 24, 1974.
Materials and Methods The small intestine was taken from nonfasted 2-month-old intact and hypophysectomized male Sprague-Dawley rats. Hypophysectomized rats weighed 200-220 g and intact rats 250-300 g. The rats and the diet (Maintenance and White diets) on which they were maintained were supplied by Simonsen Laboratory (Gilroy, California); food and water were given ad libitum. Hypophysectomized rats were given 5% glucose solution instead of drinking water and were used 2 weeks after the operation. The sella turcica and adjacent structures were examined at the time of sacrifice to ascertain completeness of hypophysectomy. Intestinal absorption was measured in vitro using the everted gut sac technique of Wilson and Wiseman (14). From nembutal-anesthetized rats, the small intestine posterior to the duodenojejunal junction was removed, rinsed
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PROLACTIN AND INTESTINAL ABSORPTION with bicarbonate-Ringer (15), everted using a thin glass rod, and placed in a plastic trough containing Ringer without glucose. The normal Ringer solution contained (mM): Na+144, K+6, Ca ++ 2.5, Mg++1.2, Cl"126, HCO 3 " 25, and D-glucose 28, pH 7.4. The Na+-free or Na+deficient solutions were prepared by replacing NaCl with equimolar choline chloride. Starting from the duodenal end, the slightly extended intestine was divided into five 12-cm long segments, numbered I-V from the proximal end. However, only segments II-V were routinely removed because in preliminary experiments segment I absorbed fluid poorly. Each sac was initially weighed empty on a Mettler H balance, and then filled with 0.8-1.0 ml of Ringer containing glucose; the open end was tied, and the sac blotted lightly and reweighed. The sac was then incubated at 37 C in a 125-ml Erlenmeyer flask containing 20 ml Ringer with glucose aerated continuously with a mixture of 95% O2 and 5% CO2. The flasks were shaken in a Dubnoff metabolic incubator at 80 oscillations/min. All sacs were prepared within 5 min of each other, and it was found that this delay did not affect their transport ability. After 1 h, the sacs were lightly blotted and reweighed; the serosal and mucosal solutions were saved for ion determinations. Na, K, Ca and Mg concentrations were measured using a Perkin-Elmer Absorption Spectrophotometer (Model 290 B) and Cl was measured using a Buchler-Cotlove Chloridometer. From knowledge of the initial and final concentrations, net fluxes of ions were calculated. Mucosal fluid and ion transport was defined as the amount of fluid or ion leaving the mucosal surface (everted lumen) entering the serosal solution and is expressed as ml of fluid or jueq of ion/g initial wet weight of sac/h. All values are expressed as the mean ± standard error, and the significance of the difference between the means was determined by the unpaired Student's t test.
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oil for intramuscular injections and simultaneously administered with prolactin in one experiment. Drugs. Phlorizin was obtained from K and K Laboratories and was introduced outside the sac (2 x 10" 4 M) (mucosal side). Ouabain was supplied by Sigma and was introduced inside the sac (1 x 10~ 4 M) (serosal side).
Results
The responses of the small intestinal segments to different doses of ovine prolactin are summarized in Tables 1-5; the effects of hypophysectomy and prolactin injections are in Table 3. As shown in Table 1, the rates of fluid, sodium, chloride and potassium absorption were increased by prolactin administration over those of the controls. The effect of the lower doses of prolactin on fluid, sodium and chloride varied depending on the gut segment; 0.25 mg PRL caused a significant increase in fluid absorption in segment II, whereas 0.5 mg PRL significantly enhanced absorption in segments II, III and IV. The stimulatory action of PRL on chloride absorption is variable; none of the doses of PRL used caused a significant increase in segment IV. Although the effects of lower doses of PRL on potassium transport were not measured in this experiment, 1.0 mg PRL significantly increased mucosal potassium transport. With higher doses of prolactin (Table 2), mucosal fluid transfer was significantly stimulated in segments III and IV by 1.0 mg PRL and in segments II, III and IV by 2.0 mg PRL. Sodium absorption was also significantly increased in segments III, IV and V by 2.0 mg PRL, but 4.0 mg failed to Hormone treatment. Ovine prolactin (oPRL: stimulate absorption of either fluid or NIH P S-9: 30 I.U./mg) was prepared for injec- sodium significantly. Prolactin generally tion by first dissolving a weighed amount in increased calcium absorption but stimula0.002M NaOH and then diluting with 0.9% NaCl tion of magnesium transport was only sigsolution to the desired concentration. Injections nificant in segment IV. were given subcutaneously to intact and As seen in Table 4, fluid and sodium hypophysectomized rats in the midafternoon 48 transport was significantly stimulated by and 24 h before the animals were killed. Vasopressin obtained from Parke-Davis (Pit- 0.1 mg PRL only in segment III and by 0.5 ressin Tannate) was diluted to 5 mU/ml sesame mg PRL in both segments. However, there The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 19 May 2015. at 16:28 For personal use only. No other uses without permission. . All rights reserved.
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TABLE 1. Effect of prolactin on mucosal fluid, Na, K and Cl transfer by the rat small intestine (segments II-IV) Mucosal transfer
Fluid (ml/g wet wt/h)
Sodium (/xeq/g wet wt/h)
Chloride (^ieq/g wet wt/h)
Potassium (/ieq/g wet wt/h)
Treatment (number)
Sac IV
Sac III
Sac II
control (10) 0.25mgPRL(10) 0.5 mgPRL(ll) 1.0 mgPRL(lO)
0.71 0.90 0.95 1.27
+ ± ± ±
0.06 0.06* 0.05** 0.08***
0.80 0.98 1.14 1.40
control (10) 0.25mgPRL (9) 0.5 mgPRL(lO) 1.0 mgPRL(lO)
65.0 110.8 103.4 144.6
± ± ± ±
11.4 18.8* 10.3* 12.9***
88.2 101.8 115.9 142.1
± ± + +
control (10) 0.25mgPRL (9) 0.5 mgPRL(lO) 1.0 mgPRL(lO)
15.7 53.1 67.9 41.3
± ± ± +
12.5 8.7* 8.8**
23.4 45.1 52.0 43.4
+ + ± ±
control (10) 1.0 mgPRL(lO)
0.75 ± 0.42 1.87 ± 0.32*
5.9
Sac V
0.87 0.96 1.17 1.53
± ± ± +
0.08 0.09 0.08* 0.10***
0.96 1.02 1.14 1.38
± + + +
0.07 0.10 0.12 0.11**
17.0 13.3* 11.9 13.3*
65.6 98.8 102.5 140.7
+ ± ± ±
16.1 13.7 14.0 13.4**
63.3 97.7 105.4 147.6
± + + ±
12.2 14.6 20.1 20.4**
7.9 9.4 9.3* 6.1
21.8 26.9 33.4 34.1
± + + +
6.9 9.1 7.3 5.9
5.2 40.5 49.3 55.7
± ± + ±
11.7 8.4* 12.9* 7.7**
± 0.07 ± 0.08 ± 0.05*** ±0.11***
1.22 ± 0.32 2.56 + 0.28**
1.01 + 0.31 2.23 ± 0.17**
0.92 ± 0.43 2.96 ± 0.30**
• 0.05 > P > 0.01; ** 0.01 > P > 0.001; *** P < 0.001, as compared with control values.
was no difference between 1.0 and 1.5 mg PRL (Table 5). Further, although chloride absorption showed some increase, the effect was not always significant (cf. Tables 4 and 5). Whereas potassium and calcium transport is significantly increased depending on the gut segment and the dose of prolactin, the effect on magnesium trans-
port is less prominent and only reaches significant levels in segment IV (Table 5). Table 3 presents the data on the effect of hypophysectomy and prolactin injections on fluid and sodium transport. Hypophysectomy significantly decreased mucosal fluid (P < 0.01) and sodium (F < 0.05) transport. Two days of prolactin
TABLE 2. Effect of prolactin on mucosal fluid, Na, Ca and Mg transfer by the rat small intestine (segments II-V) Mucosal transfer Fluid (ml/g wet wt/h)
Sodium (fieq/g wet wt/h)
Calcium (/Lteq/g wet wt/h)
Treatment (number)
Sac II
Sac III
control (8) 1.0 mg PRL (7) 2.0 mg PRL (14) 4.0 mg PRL (11)
0.75 1.08 1.06 0.78
± ± ± ±
0.12 0.09 0.06* 0.07
0.86 1.45 1.33 1.04
control (6) 1.0 mg PRL (7) 2.0 mg PRL (14) 4.0 mg PRL (11)
127.0 154.4 162.7 143.2
± ± ± ±
17.9 13.6 11.1 17.3
137.5 ± 184.6 ± 213.5 ± 159.2 ±
control (8) 1.0 mg PRL (7)
Magnesium ((JLeq/g wet wt/h) control (8) 1.0 mg PRL (7)
± ± ± ±
0.12 0.14** 0.06*** 0.09 19.5 14.3 17.8* 13.0
Sac IV 1.11 1.62 1.59 1.30 149.7 245.3 216.3 195.8
±0.16 ± 0.08* ± 0.08** ± 0.10 ± ± ± ±
SacV 0.97 1.19 1.30 1.10
± ± ± ±
0.19 0.09 0.07 0.05
20.1 15.2** 10.9** 14.4
139.1 ± 23.7 194.6 ± 25.8 188.2 ± 12.1* 170.1 ± 11.0
0.72 ± 0.18 1.32 ± 0.14*
1.13 ± 0.14 1.97 ± 0.43
1.03 ± 0.25 2.17 ±0.23**
0.68 ± 0.29 1.63 ± 0.27*
0.66 ±0.11 1.00 ± 0.15
0.94 ±0.11 1.07 ± 0.16
0.83 ± 0.14 1.30 ± 0.17*
0.85 ± 0.17 1.05 ± 0.13
* 0.05 > P > 0.01; ** 0.01 > P > 0.001; *** P < 0.001, as compared with control values.
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PROLACTIN AND INTESTINAL ABSORPTION
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TABLE 3. Effect of prolactin on mucosal fluid and Na transfer by the rat small intestine (segments II-V) Treatment (number)
Mucosal transfer Fluid (ml/g wet wt/h)
control (6) HX + saline (6) HX + 0.1mgPRL(5) HX + 1.0 mg PRL (6) HX + 4.0 mg PRL (5)
Sodium (jteq/g wet wt/h)
control (6) HX + saline (6) HX +0.1 ing PRL (5) HX + 1.0 mg PRL (6) HX + 4.0 mg PRL (5)
0.77 0.34 0.57 0.83 0.43
Sac IV
Sac III
Sac II
± 0.10** ± 0.08 ± 0.19 ± 0.17* ± 0.03
111.1 ± 17.2* 57.0 ± 15.6 77.2 ± 30.0 125.0 ± 28.4 58.5 ± 8.6
1.02 0.46 0.82 0.95 0.72
± 0.09** ± 0.12 ± 0.16 ± 0.14* ± 0.10
145.4 62.8 104.8 127.2 105.8
± 12.2** ± 19.0 ± 19.7 ± 21.7* ± 17.2
1.15 0.49 1.04 1.02 0.66
± 0.10*** ± 0.04 ± 0.22* ± 0.10** ± 0.23
162.9 ± 66.4 ± 127.3 ± 124.6 ± 71.2 ±
13.3*** 11.3 29.7 20.1* 22.8
Sac V
0.96 0.42 0.85 0.82 0.61
± 0.04** ± 0.14 ± 0.19 + 0.11* ± 0.12
134.5 ± 18.1* 55.4 ± 20.1 121.7 ± 24.8 113.3 ±21.6 112.9 ± 27.5
* 0.05 > P > 0.01; **0.01 >P > 0.001; *** P < 0.001, as compared with hypophysectomized (HX) values.
(0.1 and 1.0 mg) treatment restored fluid and sodium absorption in some segments nearly to normal levels. Again 4.0 mg PRL failed to restore absorption to normal in several segments. The effects of vasopressin on mucosal fluid and NaCl transfer and its effects on prolactin action are shown in Table 6. Although vasopressin alone does not seem to
have much effect on jejunal fluid and sodium absorption, it completely blocked the stimulatory action of prolactin on fluid and NaCl transport; when given simultaneously with prolactin it significantly inhibited chloride absorption in segment IV. The possibility that prolactin increases absorptive capacity of the small intestine independently of active sodium transport
TABLE 4. Effect of ovine prolactin on fluid and ion transfer by the rat jejunum
Treatment (number)
Mucosal fluid transfer (ml/g wet wt/h)
Mucosal Na+ transfer (jteq/g wet wt/h)
Mucosal Cl~ transfer (neq/g wet wt/h)
Mucosal K+ transfer (fxeq/g wet wt/h)
Mucosal Ca f+ transfer (/xeq/g wet wt/h)
III
control (7) 0.1 mg PRL (7) 0.5 mg PRL (7) 1.0 mg PRL (7)
0.74 ± 0.09 1.19 + 0.11** 1.46 + 0.08*** 1.48 + 0.08***
114.0 ± 16.1 185.8 ± 14.5** 225.8 ± 16.4*** 226.9 + 20.9***
22.2 + 8.5 33.2 ± 4.4 32.8 + 4.7 33.3 + 7.6
1.58 ± 0.85 2.96 + 0.94 3.60 + 0.37* 4.02 ± 0.71*
0.68 ± 0.23 1.70 + 0.21** 1.68 ± 0.19** 2.08 + 0.22***
IV
control (7) 0.1 mg PRL (7) 0.5 mg PRL (7) 1.0 mg PRL (7)
1.08 1.34 1.64 1.76
163.9 ± 18.4 206.4 ± 15.9 223.7 ± 8.5* 248.0 ± 18.5**
27.9 ± 27.5 + 28.9 ± 35.7 ±
2.16 3.19 3.64 4.44
1.57 1.95 1.69 2.54
Jejunal sac
± 0.10 + 0.11 ± 0.06*** ± 0.08***
6.7 5.1 4.8 7.9
± ± ± +
0.80 0.81 0.29 0.82
± 0.23 + 0.24 ± 0.12 ± 0.22*
Mucosal Mg++ transfer (/ieq/g wet wt/h) -0.04 0.57 0.21 0.48 0.44 0.72 0.71 0.55
± 0.22 + 0.22 ± 0.18 + 0.17 ± ± + ±
0.13 0.43 0.14 0.09
* 0.05 > P > 0.01; ** 0.01 > P > 0.001; *** P < 0.001, as compared with control values. TABLE 5. Effect of ovine prolactin on fluid and ion transfer by rat jejunum
Treatment
Mucosal fluid transfer (ml/g wet wt/h)
Mucosal Na+ transfer (fieqlg wet wt/h)
Mucosal Cl" transfer (/xeq/g wet wt/h)
Mucosal K+ transfer (fieq/g wet wt/h)
Mucosal Ca+* transfer (fieqlg wet wt/h)
Mucosal Mg++ transfer (lieqlg wet wt/h)
III
control (10) 1.0 mg PRL (11) 1.5 mg PRL (6)
1.09 ± 0.09 1.79 ± 0.09*** 1.81 ± 0.09***
140.5 ± 11.2 242.8 ± 16.2*** 259.9 ± 11.3***
35.3 a= 6.0 60.5 Ht9.6* 73.4 it 3.2***
1.51 ± 0.41 4.35 ± 0.81** 2.58 ± 0.44
0.84 ± 0.14 1.39 ± 0.17* 1.45 ± 0.10**
0.48 ± 0.15 0.99 ± 0.20 0.64 ± 0.11
IV
control (10) 1.0 mg PRL (11) 1.5 mg PRL (6)
1.12 ± 0.05 1.81 ± 0.08*** 1.84 ± 0.10***
133.8+ 7.3 230.5 ± 14.7*** 234.8 ± 16.5"*
26.0 it5.4 41.4 it9.4 68.9 ± 6.8***
0.99 ± 0.32 3.90 ± 0.64*** 2.46 ± 0.62*
0.70 ±0.14 1.64 ± 0.22** 1.63 ± 0.26**
0.61 ± 0.19 0.97 ± 0.22* 0.72 ± 0.13
Jejunal snc
* 0.05 > P > 0.01; ** 0.01 >P > 0.001; **• P < 0.001, as compared with control values.
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TABLE 6. Effect of prolactin and arginine vasopressin (ADH) on fluid and NaCl transfer by the rat jejunum Mucosal fluid transfer (ml/g wet wt/h)
Mucosal Na+ transfer (/xeq/g wet wt/h)
control (6)
1.06 ± 0.06
135.7 ± 12.5
38.6 ± 7.3
1.0 mg PRL (7)
1.66 ± 0.12**
221.0 ± 10.4***
77.0 ± 8.0**
1.0 mg PRL + 5 mU ADH (6)
0.93 ± 0.07
123.5 ± 16.7
24.2 ± 9.3
5 mU ADH (6)
1.03 ± 0.11
130.5 ± 16.3
25.9 ± 12.1
control (6)
1.15 ± 0.07
133.7 ± 10.3
22.1 ± 3.2
1.0 mg PRL (7)
1.96 ± 0.14***
234.2 ± 11.5***
66.0 ± 10.4**
1.0 mg PRL + 5 mU ADH (6)
1.06 ± 0.08
129.5 ± 6.4
12.1 ± 2.7*
5 mU ADH (6)
1.27 ± 0.13
148.1 ± 20.0
21.5 ± 9.7
Jejunal segment III
IV
Treatment (number)
Mucosal Cl~ transfer (fieq/g wet wt/h)
* 0.05 > P > 0.01; ** 0.01 > P > 0.001; *** P < 0.001, as compared with control values.
was examined by varying ambient incubation conditions; the results using segment IV are shown in Table 7. In normal Ringer, PRL enhanced fluid and sodium absorption by 60% and 98%, respectively. However, omission of glucose or reduction in ambient mucosal sodium concentrations decreased absorption. Also the presence of 2 x 10~4 M phlorizin in the mucosal solution or 1 x 10~4 M ouabain in the serosal
solution dramatically decreased fluid and sodium absorption. Discussion Although the osmoregulatory action of prolactin in mammals has not been examined systematically, accumulating evidence indicates that prolactin administration results in marked antidiuresis and antisaluresis in rats, cats (5,16), sheep (17,
TABLE 7. Effect of prolactin on mucosal fluid and Na transfer by the rat jejunum (segment IV) under different incubation conditions Treatment (number)
Mucosal fluid transfer (ml/g wet wt/h)
Mucosal Na+ transfer (pieq/g wet wt/h)
control (5) 1.0 mg PRL (4)
0.99 ± 0.08 1.59 ± 0.12**
107.9 ± 16.9 214.0 ± 26.1**
control (5) 2.0 mg PRL (4)
0.52 ± 0.04*** 0.47 ± 0.05***
92.0 ± 9.4 84.5 ± 11.4
control (6) 1.0 mg PRL (6)
0.20 ± 0.02*** 0.24 ± 0.02***
23.9 ± 3.1*** 27.4 ± 2.6***
control (4) 1.0 mg PRL (4)
0.69 ± 0.07* 0.69 ± 0.09*
83.8 ± 7.9 77.1 ± 8.3
Ouabain (1 x 10~ 4 M)
control (4) 1.0 mg PRL (4)
0.46 ± 0.09** 0.49 ± 0.09**
20.4 ± 8.6** 15.8 ± 9.0**
Na-free Ringer .
control (4) 1.0 mg PRL (4)
0.19 ± 0.06*** 0.15 ± 0.02***
Incubation condition Normal Ringer (145 meq/liter Na+) Normal Ringer (glucose absent) Phlorizin (2 x 10"4 M) Choline chloride-Ringer (28 meq/liter Na+)
* 0.05 > P > 0.01; ** 0.01 > P > 0.001; *** P < 0.001, as compared with normal Ringer control values.
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PROLACTIN AND INTESTINAL ABSORPTION
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jejunum and ileum are also capable of active calcium transport especially under conditions of low calcium intake (23). Furthermore, Finkelstein and Schachter (24) showed that bovine growth hormone and to a less extent ovine prolactin stimulated active absorption of calcium by hypophysectomized rat duodenum in vivo. Evidence is presented herein showing that prolactin treatment significantly stimulates calcium absorption by the rat jejunum. The data obtained in the present experiments indicate that although prolactin may enhance magnesium absorption, the effect rarely reaches significant levels. The mechanism(s) by which prolactin stimulates fluid and ion absorption is uncertain. Also intriguing is the failure of larger doses of prolactin to stimulate intestinal absorption (the 2 and 4 mg daily doses are presumably "supraphysiological"). Angiotensin had been shown to stimulate sodium and water transport at low concentrations and to inhibit at higher concentrations (25). It is possible that prolactin has a biphasic action on jejunal fluid and sodium transport similar to that of angiotensin. Another explanation lies in the possible contamination of prolactin with vasopressin. In the rat and man (26, 27) administration of vasopressin inhibited water and NaCl absorption by the jejunum and ileum in vivo and in some instances resulted in net salt and water secretion. Conversely, vasopressin stimulates fluid and sodium transport in the rat colon (25) and mouse colon (28), an action evidently mediated by cyclic adenosine monophosphate. Because vasopressin antagonized the effects of prolactin on jejunal absorption, it is conceivable that its possible presence as a contaminant could account for the lack of effect of larger doses of prolactin. It is generally known that ouabain inhibits sodium transport, whereas phlorizin inhibits glucose transport and, at higher doses, metabolism (29). The low rates of Although maximal active calcium trans- fluid and sodium absorption observed in port occurs in the duodenum, the rat glucose-free Ringer or in the presence of
18) and man (6). Furthermore, ovine prolactin has been shown to stimulate fluid transport in the rat jejunum, an effect which is independent of the adrenal and the renin-angiotensin system (12). The results of the present study indicate that ovine prolactin is not only highly effective in stimulating fluid and sodium absorption by the rat jejunum, but also significantly enhances mucosal transfer of chloride, potassium and calcium and occasionally magnesium. Though reports on the effect of hypophysectomy on intestinal absorption are inconclusive (10), Righetti and Levitan (19) have shown that water, salt and glucose absorption in vivo is decreased by 50% following hypophysectomy. The results presented herein also demonstrated that hypophysectomy caused a significant decrease in mucosal fluid and sodium transport and that optimal doses of ovine prolactin restored absorption in most segments to normal levels. In the intact and hypophysectomized rats, prolactin action on fluid and sodium absorption showed a dose-related tendency, especially in the midjejunal segments (III and IV) in some experiments. In the jejunum, chloride absorption does not appear to be related to sodium transport in any simple fashion. Prolactin, however, augments chloride absorption especially in the more proximal and distal jejunal segments. The observations of Tidball (20) and Taylor et al. (21) that the jejunum sometimes actively secretes chloride into the lumen could explain why prolactin did not stimulate consistently and significantly chloride absorption in segment IV. Compared with other ions, potassium absorption has received relatively little attention. There are indications that in the intestinal mucosa sodium and potassium transport mechanisms may be linked (22). As shown in this study, the jejunum from prolactin-injected rats showed a significant increase in mucosal potassium transport.
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phlorizin indicated that the facilitatory actions of prolactin on jejunal transport are glucose-dependent. However, absence of glucose from the medium only slightly decreased the basal level of fluid and sodium transport but completely abolished the prolactin-stimulated transport. Much of this basal transport level could be sustained by endogenous glucose in the gut tissue (29). Basal fluid and sodium transport is further decreased by phlorizin possibly because it inhibits glucose-dependent transport and the glycolytic breakdown of glucose which in the jejunum provides energy for the transport of other solutes (11,29,30). When the sacs were incubated in Ringer containing low mucosal sodium concentration or in the presence of ouabain, an inhibition of fluid transport was also observed. These observations are in agreement with the hypothesis that sodium and glucose transport are interdependent and that water transport is dependent on solute transport (30). In any case, the present data demonstrate that prolactin administration effectively stimulates mechanism(s) involved in the regulation of fluid and ion movement across the intestinal mucosa. It is further suggested that prolactin may enhance fluid and ion absorption by stimulating active sodium transport. Of importance in osmoregulation is the ability to conserve water and ions when needed; this makes the regulation of fluid and salt transport by the mammalian intestine desirable in situations such as dehydration, gestation and lactation. In the last two circumstances, at least, high blood prolactin (including placental lactogen) levels would be expected to play a significant physiological role (cf. 31). Acknowledgments Aided by NIH Grant CA-05388 and a Rockefeller Foundation Fellowship. I am grateful to Professor Howard A. Bern for his support and guidance throughout this study and for his valuable criticism of the manuscript. oPRL generously provided by NIAMDD.
References 1. Bern, H. A., and C. S. Nicoll, Recent Progr Horm Res 24: 681, 1968. 2. Nicoll, C. S., and H. A. Bern, In Wolstenholme, G. E. W., and J. Knight (eds.), Lactogenic Hormones, Churchill and Livingston, London, 1972, p. 299. 3. Ensor, D. M., and J. N. Ball, Fed Proc 31: 1615, 1972. 4. Lam, T. J., Gen Comp Endocrinol Suppl 3: 328, 1972. 5. Lockett, M. F.J Physiol 181: 192, 1965. 6. Horrobin, D. F., P. G. Burstyn, I. J. Lloyd, N. Durkin, A. Lipton, and K. L. Muiruri, Lancet ii: 352, 1971. 7. Buckman, M. T., and G. T. Peake, Science 181: 755, 1973. 8. Relkin, R., Neuroendocrinology 14: 61, 1974. 9. Ensor, D. M., M. R. Edmondson, and J. G. Phillips, J Endocrinol 53: lix, 1972. 10. Levin, R. J.J Endocrinol 45: 315, 1969. 11. Matty, A. J., and H. M. Noble, Hormones 3: 42, 1972. 12. Ramsey, D. H., and H. A. Bern, J Endocrinol 53: 453, 1972. 13. Mainoya, J. R., H. A. Bern, and J. W. Regan, J Endocrinol 63: 311, 1974. 14. Wilson, T. H., and G. W. Wiseman, J Physiol 123: 116, 1954. 15. Krebs, H. A., and K. Henseleit, Hoppe-Seyler's.Z Physiol Chem 210: 33, 1932. 16. Lockett, M. F., and B. Nail, J Physiol 180: 147, 1965. 17. Burstyn, P. G., D. F. Horrobin, and M. S. Manku, J Endocrinol 55: 369, 1972. 18. Horrobin, D. F., M. S. Manku, and P. G. Burstyn, J Endocrinol 56: 343, 1973. 19. Righetti, A., and R. Levitan, Am J Digest Dis 15: 218, 1970. 20. Tidball, C. S., Am J Physiol 200: 309, 1961. 21. Taylor, A. E., E. M. Wright, S. G. Schultz, and P. F. Curran, AmJ Physiol 214: 836, 1968. 22. Parsons, D. S., Br Med Bull 23: 252, 1967. 23. Kimberg, D. V., D. Schachter, and H. Schenker, AmJ Physiol 200: 1256, 1961. 24. Finkelstein, J. D., and D. Schachter, AmJ Physiol 203: 873, 1962. 25. Homych, A., P. Meyer, and P. Milliez, Am J Physiol 224: 1223, 1973. 26. Dennhardt, R., and F. J. Haberich, Pfliigers Arch 334: 74, 1972. 27. Soergel, K. H., G. E. Whalen, J. A. Harris, and J. E. Green, 7 Clin Invest 47: 1071, 1968. 28. Green, K., and A. J. Matty, Life Sci 5: 205, 1966. 29. Gilman, A., and E. S. Koelle, Am J Physiol 199: 1025, 1960. 30. Schultz, S. G., and P. F. Curran, Physiol Rev 50: 637, 1970. 31. Mainoya, J. R., Am Zool 14: 1244, 1974.
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of prolactin was inhibited by a simultaneous administration of vasopressin which when given alone had no effect on intestinal absorption. In the absence of glucose or in the presence of phlorizin, fluid transport was inhibited, the reduction being more dramatic in the presence of phlorizin. Similarly, either application of ouabain or partial replacement of sodium with isotonic choline chloride reduced fluid transport. Although these in vitro treatments nullified the stimulatory effects of prolactin, only phlorizin and ouabain significantly decreased sodium transport. These results suggest that the effects of prolactin on intestinal transport may be dependent on increased movement of sodium. (Endocrinology 96: 1158, 1975)
AMONG the many and diverse actions -t\. of prolactin in the vertebrates (1,2). an important contribution to osmoregulation has been demonstrated in teleost fish (3,4) and indicated in other nonmammalian vertebrates. Assessment of the role of prolactin in hydromineral metabolism in mammals has been based mainly on two experimental results: either the increased ability of the prolactin-treated animal to retain water, sodium and potassium (5,6) or changes in plasma prolactin levels in response to osmotic challenges (7,8). Ensoref al. (9) reported that in female rats dehydration was associated with a decrease in pituitary prolactin levels and suggested that prolactin might stimulate increased fluid intake especially during lactation. Much evidence indicates that certain hormonal states may influence intestinal absorption of water and solutes (10,11); however, reports on the effects of adenohypophysial hormones on intestinal absorption are scarce. Although it has been demonstrated that prolactin administration
significantly stimulated fluid absorption by the rat small intestine (12,13), little is known of the action of prolactin on intestinal absorption of ions. The present experiments were designed to investigate the effects of prolactin on fluid and ion absorption by the rat jejunum.
Received June 24, 1974.
Materials and Methods The small intestine was taken from nonfasted 2-month-old intact and hypophysectomized male Sprague-Dawley rats. Hypophysectomized rats weighed 200-220 g and intact rats 250-300 g. The rats and the diet (Maintenance and White diets) on which they were maintained were supplied by Simonsen Laboratory (Gilroy, California); food and water were given ad libitum. Hypophysectomized rats were given 5% glucose solution instead of drinking water and were used 2 weeks after the operation. The sella turcica and adjacent structures were examined at the time of sacrifice to ascertain completeness of hypophysectomy. Intestinal absorption was measured in vitro using the everted gut sac technique of Wilson and Wiseman (14). From nembutal-anesthetized rats, the small intestine posterior to the duodenojejunal junction was removed, rinsed
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PROLACTIN AND INTESTINAL ABSORPTION with bicarbonate-Ringer (15), everted using a thin glass rod, and placed in a plastic trough containing Ringer without glucose. The normal Ringer solution contained (mM): Na+144, K+6, Ca ++ 2.5, Mg++1.2, Cl"126, HCO 3 " 25, and D-glucose 28, pH 7.4. The Na+-free or Na+deficient solutions were prepared by replacing NaCl with equimolar choline chloride. Starting from the duodenal end, the slightly extended intestine was divided into five 12-cm long segments, numbered I-V from the proximal end. However, only segments II-V were routinely removed because in preliminary experiments segment I absorbed fluid poorly. Each sac was initially weighed empty on a Mettler H balance, and then filled with 0.8-1.0 ml of Ringer containing glucose; the open end was tied, and the sac blotted lightly and reweighed. The sac was then incubated at 37 C in a 125-ml Erlenmeyer flask containing 20 ml Ringer with glucose aerated continuously with a mixture of 95% O2 and 5% CO2. The flasks were shaken in a Dubnoff metabolic incubator at 80 oscillations/min. All sacs were prepared within 5 min of each other, and it was found that this delay did not affect their transport ability. After 1 h, the sacs were lightly blotted and reweighed; the serosal and mucosal solutions were saved for ion determinations. Na, K, Ca and Mg concentrations were measured using a Perkin-Elmer Absorption Spectrophotometer (Model 290 B) and Cl was measured using a Buchler-Cotlove Chloridometer. From knowledge of the initial and final concentrations, net fluxes of ions were calculated. Mucosal fluid and ion transport was defined as the amount of fluid or ion leaving the mucosal surface (everted lumen) entering the serosal solution and is expressed as ml of fluid or jueq of ion/g initial wet weight of sac/h. All values are expressed as the mean ± standard error, and the significance of the difference between the means was determined by the unpaired Student's t test.
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oil for intramuscular injections and simultaneously administered with prolactin in one experiment. Drugs. Phlorizin was obtained from K and K Laboratories and was introduced outside the sac (2 x 10" 4 M) (mucosal side). Ouabain was supplied by Sigma and was introduced inside the sac (1 x 10~ 4 M) (serosal side).
Results
The responses of the small intestinal segments to different doses of ovine prolactin are summarized in Tables 1-5; the effects of hypophysectomy and prolactin injections are in Table 3. As shown in Table 1, the rates of fluid, sodium, chloride and potassium absorption were increased by prolactin administration over those of the controls. The effect of the lower doses of prolactin on fluid, sodium and chloride varied depending on the gut segment; 0.25 mg PRL caused a significant increase in fluid absorption in segment II, whereas 0.5 mg PRL significantly enhanced absorption in segments II, III and IV. The stimulatory action of PRL on chloride absorption is variable; none of the doses of PRL used caused a significant increase in segment IV. Although the effects of lower doses of PRL on potassium transport were not measured in this experiment, 1.0 mg PRL significantly increased mucosal potassium transport. With higher doses of prolactin (Table 2), mucosal fluid transfer was significantly stimulated in segments III and IV by 1.0 mg PRL and in segments II, III and IV by 2.0 mg PRL. Sodium absorption was also significantly increased in segments III, IV and V by 2.0 mg PRL, but 4.0 mg failed to Hormone treatment. Ovine prolactin (oPRL: stimulate absorption of either fluid or NIH P S-9: 30 I.U./mg) was prepared for injec- sodium significantly. Prolactin generally tion by first dissolving a weighed amount in increased calcium absorption but stimula0.002M NaOH and then diluting with 0.9% NaCl tion of magnesium transport was only sigsolution to the desired concentration. Injections nificant in segment IV. were given subcutaneously to intact and As seen in Table 4, fluid and sodium hypophysectomized rats in the midafternoon 48 transport was significantly stimulated by and 24 h before the animals were killed. Vasopressin obtained from Parke-Davis (Pit- 0.1 mg PRL only in segment III and by 0.5 ressin Tannate) was diluted to 5 mU/ml sesame mg PRL in both segments. However, there The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 19 May 2015. at 16:28 For personal use only. No other uses without permission. . All rights reserved.
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TABLE 1. Effect of prolactin on mucosal fluid, Na, K and Cl transfer by the rat small intestine (segments II-IV) Mucosal transfer
Fluid (ml/g wet wt/h)
Sodium (/xeq/g wet wt/h)
Chloride (^ieq/g wet wt/h)
Potassium (/ieq/g wet wt/h)
Treatment (number)
Sac IV
Sac III
Sac II
control (10) 0.25mgPRL(10) 0.5 mgPRL(ll) 1.0 mgPRL(lO)
0.71 0.90 0.95 1.27
+ ± ± ±
0.06 0.06* 0.05** 0.08***
0.80 0.98 1.14 1.40
control (10) 0.25mgPRL (9) 0.5 mgPRL(lO) 1.0 mgPRL(lO)
65.0 110.8 103.4 144.6
± ± ± ±
11.4 18.8* 10.3* 12.9***
88.2 101.8 115.9 142.1
± ± + +
control (10) 0.25mgPRL (9) 0.5 mgPRL(lO) 1.0 mgPRL(lO)
15.7 53.1 67.9 41.3
± ± ± +
12.5 8.7* 8.8**
23.4 45.1 52.0 43.4
+ + ± ±
control (10) 1.0 mgPRL(lO)
0.75 ± 0.42 1.87 ± 0.32*
5.9
Sac V
0.87 0.96 1.17 1.53
± ± ± +
0.08 0.09 0.08* 0.10***
0.96 1.02 1.14 1.38
± + + +
0.07 0.10 0.12 0.11**
17.0 13.3* 11.9 13.3*
65.6 98.8 102.5 140.7
+ ± ± ±
16.1 13.7 14.0 13.4**
63.3 97.7 105.4 147.6
± + + ±
12.2 14.6 20.1 20.4**
7.9 9.4 9.3* 6.1
21.8 26.9 33.4 34.1
± + + +
6.9 9.1 7.3 5.9
5.2 40.5 49.3 55.7
± ± + ±
11.7 8.4* 12.9* 7.7**
± 0.07 ± 0.08 ± 0.05*** ±0.11***
1.22 ± 0.32 2.56 + 0.28**
1.01 + 0.31 2.23 ± 0.17**
0.92 ± 0.43 2.96 ± 0.30**
• 0.05 > P > 0.01; ** 0.01 > P > 0.001; *** P < 0.001, as compared with control values.
was no difference between 1.0 and 1.5 mg PRL (Table 5). Further, although chloride absorption showed some increase, the effect was not always significant (cf. Tables 4 and 5). Whereas potassium and calcium transport is significantly increased depending on the gut segment and the dose of prolactin, the effect on magnesium trans-
port is less prominent and only reaches significant levels in segment IV (Table 5). Table 3 presents the data on the effect of hypophysectomy and prolactin injections on fluid and sodium transport. Hypophysectomy significantly decreased mucosal fluid (P < 0.01) and sodium (F < 0.05) transport. Two days of prolactin
TABLE 2. Effect of prolactin on mucosal fluid, Na, Ca and Mg transfer by the rat small intestine (segments II-V) Mucosal transfer Fluid (ml/g wet wt/h)
Sodium (fieq/g wet wt/h)
Calcium (/Lteq/g wet wt/h)
Treatment (number)
Sac II
Sac III
control (8) 1.0 mg PRL (7) 2.0 mg PRL (14) 4.0 mg PRL (11)
0.75 1.08 1.06 0.78
± ± ± ±
0.12 0.09 0.06* 0.07
0.86 1.45 1.33 1.04
control (6) 1.0 mg PRL (7) 2.0 mg PRL (14) 4.0 mg PRL (11)
127.0 154.4 162.7 143.2
± ± ± ±
17.9 13.6 11.1 17.3
137.5 ± 184.6 ± 213.5 ± 159.2 ±
control (8) 1.0 mg PRL (7)
Magnesium ((JLeq/g wet wt/h) control (8) 1.0 mg PRL (7)
± ± ± ±
0.12 0.14** 0.06*** 0.09 19.5 14.3 17.8* 13.0
Sac IV 1.11 1.62 1.59 1.30 149.7 245.3 216.3 195.8
±0.16 ± 0.08* ± 0.08** ± 0.10 ± ± ± ±
SacV 0.97 1.19 1.30 1.10
± ± ± ±
0.19 0.09 0.07 0.05
20.1 15.2** 10.9** 14.4
139.1 ± 23.7 194.6 ± 25.8 188.2 ± 12.1* 170.1 ± 11.0
0.72 ± 0.18 1.32 ± 0.14*
1.13 ± 0.14 1.97 ± 0.43
1.03 ± 0.25 2.17 ±0.23**
0.68 ± 0.29 1.63 ± 0.27*
0.66 ±0.11 1.00 ± 0.15
0.94 ±0.11 1.07 ± 0.16
0.83 ± 0.14 1.30 ± 0.17*
0.85 ± 0.17 1.05 ± 0.13
* 0.05 > P > 0.01; ** 0.01 > P > 0.001; *** P < 0.001, as compared with control values.
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PROLACTIN AND INTESTINAL ABSORPTION
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TABLE 3. Effect of prolactin on mucosal fluid and Na transfer by the rat small intestine (segments II-V) Treatment (number)
Mucosal transfer Fluid (ml/g wet wt/h)
control (6) HX + saline (6) HX + 0.1mgPRL(5) HX + 1.0 mg PRL (6) HX + 4.0 mg PRL (5)
Sodium (jteq/g wet wt/h)
control (6) HX + saline (6) HX +0.1 ing PRL (5) HX + 1.0 mg PRL (6) HX + 4.0 mg PRL (5)
0.77 0.34 0.57 0.83 0.43
Sac IV
Sac III
Sac II
± 0.10** ± 0.08 ± 0.19 ± 0.17* ± 0.03
111.1 ± 17.2* 57.0 ± 15.6 77.2 ± 30.0 125.0 ± 28.4 58.5 ± 8.6
1.02 0.46 0.82 0.95 0.72
± 0.09** ± 0.12 ± 0.16 ± 0.14* ± 0.10
145.4 62.8 104.8 127.2 105.8
± 12.2** ± 19.0 ± 19.7 ± 21.7* ± 17.2
1.15 0.49 1.04 1.02 0.66
± 0.10*** ± 0.04 ± 0.22* ± 0.10** ± 0.23
162.9 ± 66.4 ± 127.3 ± 124.6 ± 71.2 ±
13.3*** 11.3 29.7 20.1* 22.8
Sac V
0.96 0.42 0.85 0.82 0.61
± 0.04** ± 0.14 ± 0.19 + 0.11* ± 0.12
134.5 ± 18.1* 55.4 ± 20.1 121.7 ± 24.8 113.3 ±21.6 112.9 ± 27.5
* 0.05 > P > 0.01; **0.01 >P > 0.001; *** P < 0.001, as compared with hypophysectomized (HX) values.
(0.1 and 1.0 mg) treatment restored fluid and sodium absorption in some segments nearly to normal levels. Again 4.0 mg PRL failed to restore absorption to normal in several segments. The effects of vasopressin on mucosal fluid and NaCl transfer and its effects on prolactin action are shown in Table 6. Although vasopressin alone does not seem to
have much effect on jejunal fluid and sodium absorption, it completely blocked the stimulatory action of prolactin on fluid and NaCl transport; when given simultaneously with prolactin it significantly inhibited chloride absorption in segment IV. The possibility that prolactin increases absorptive capacity of the small intestine independently of active sodium transport
TABLE 4. Effect of ovine prolactin on fluid and ion transfer by the rat jejunum
Treatment (number)
Mucosal fluid transfer (ml/g wet wt/h)
Mucosal Na+ transfer (jteq/g wet wt/h)
Mucosal Cl~ transfer (neq/g wet wt/h)
Mucosal K+ transfer (fxeq/g wet wt/h)
Mucosal Ca f+ transfer (/xeq/g wet wt/h)
III
control (7) 0.1 mg PRL (7) 0.5 mg PRL (7) 1.0 mg PRL (7)
0.74 ± 0.09 1.19 + 0.11** 1.46 + 0.08*** 1.48 + 0.08***
114.0 ± 16.1 185.8 ± 14.5** 225.8 ± 16.4*** 226.9 + 20.9***
22.2 + 8.5 33.2 ± 4.4 32.8 + 4.7 33.3 + 7.6
1.58 ± 0.85 2.96 + 0.94 3.60 + 0.37* 4.02 ± 0.71*
0.68 ± 0.23 1.70 + 0.21** 1.68 ± 0.19** 2.08 + 0.22***
IV
control (7) 0.1 mg PRL (7) 0.5 mg PRL (7) 1.0 mg PRL (7)
1.08 1.34 1.64 1.76
163.9 ± 18.4 206.4 ± 15.9 223.7 ± 8.5* 248.0 ± 18.5**
27.9 ± 27.5 + 28.9 ± 35.7 ±
2.16 3.19 3.64 4.44
1.57 1.95 1.69 2.54
Jejunal sac
± 0.10 + 0.11 ± 0.06*** ± 0.08***
6.7 5.1 4.8 7.9
± ± ± +
0.80 0.81 0.29 0.82
± 0.23 + 0.24 ± 0.12 ± 0.22*
Mucosal Mg++ transfer (/ieq/g wet wt/h) -0.04 0.57 0.21 0.48 0.44 0.72 0.71 0.55
± 0.22 + 0.22 ± 0.18 + 0.17 ± ± + ±
0.13 0.43 0.14 0.09
* 0.05 > P > 0.01; ** 0.01 > P > 0.001; *** P < 0.001, as compared with control values. TABLE 5. Effect of ovine prolactin on fluid and ion transfer by rat jejunum
Treatment
Mucosal fluid transfer (ml/g wet wt/h)
Mucosal Na+ transfer (fieqlg wet wt/h)
Mucosal Cl" transfer (/xeq/g wet wt/h)
Mucosal K+ transfer (fieq/g wet wt/h)
Mucosal Ca+* transfer (fieqlg wet wt/h)
Mucosal Mg++ transfer (lieqlg wet wt/h)
III
control (10) 1.0 mg PRL (11) 1.5 mg PRL (6)
1.09 ± 0.09 1.79 ± 0.09*** 1.81 ± 0.09***
140.5 ± 11.2 242.8 ± 16.2*** 259.9 ± 11.3***
35.3 a= 6.0 60.5 Ht9.6* 73.4 it 3.2***
1.51 ± 0.41 4.35 ± 0.81** 2.58 ± 0.44
0.84 ± 0.14 1.39 ± 0.17* 1.45 ± 0.10**
0.48 ± 0.15 0.99 ± 0.20 0.64 ± 0.11
IV
control (10) 1.0 mg PRL (11) 1.5 mg PRL (6)
1.12 ± 0.05 1.81 ± 0.08*** 1.84 ± 0.10***
133.8+ 7.3 230.5 ± 14.7*** 234.8 ± 16.5"*
26.0 it5.4 41.4 it9.4 68.9 ± 6.8***
0.99 ± 0.32 3.90 ± 0.64*** 2.46 ± 0.62*
0.70 ±0.14 1.64 ± 0.22** 1.63 ± 0.26**
0.61 ± 0.19 0.97 ± 0.22* 0.72 ± 0.13
Jejunal snc
* 0.05 > P > 0.01; ** 0.01 >P > 0.001; **• P < 0.001, as compared with control values.
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TABLE 6. Effect of prolactin and arginine vasopressin (ADH) on fluid and NaCl transfer by the rat jejunum Mucosal fluid transfer (ml/g wet wt/h)
Mucosal Na+ transfer (/xeq/g wet wt/h)
control (6)
1.06 ± 0.06
135.7 ± 12.5
38.6 ± 7.3
1.0 mg PRL (7)
1.66 ± 0.12**
221.0 ± 10.4***
77.0 ± 8.0**
1.0 mg PRL + 5 mU ADH (6)
0.93 ± 0.07
123.5 ± 16.7
24.2 ± 9.3
5 mU ADH (6)
1.03 ± 0.11
130.5 ± 16.3
25.9 ± 12.1
control (6)
1.15 ± 0.07
133.7 ± 10.3
22.1 ± 3.2
1.0 mg PRL (7)
1.96 ± 0.14***
234.2 ± 11.5***
66.0 ± 10.4**
1.0 mg PRL + 5 mU ADH (6)
1.06 ± 0.08
129.5 ± 6.4
12.1 ± 2.7*
5 mU ADH (6)
1.27 ± 0.13
148.1 ± 20.0
21.5 ± 9.7
Jejunal segment III
IV
Treatment (number)
Mucosal Cl~ transfer (fieq/g wet wt/h)
* 0.05 > P > 0.01; ** 0.01 > P > 0.001; *** P < 0.001, as compared with control values.
was examined by varying ambient incubation conditions; the results using segment IV are shown in Table 7. In normal Ringer, PRL enhanced fluid and sodium absorption by 60% and 98%, respectively. However, omission of glucose or reduction in ambient mucosal sodium concentrations decreased absorption. Also the presence of 2 x 10~4 M phlorizin in the mucosal solution or 1 x 10~4 M ouabain in the serosal
solution dramatically decreased fluid and sodium absorption. Discussion Although the osmoregulatory action of prolactin in mammals has not been examined systematically, accumulating evidence indicates that prolactin administration results in marked antidiuresis and antisaluresis in rats, cats (5,16), sheep (17,
TABLE 7. Effect of prolactin on mucosal fluid and Na transfer by the rat jejunum (segment IV) under different incubation conditions Treatment (number)
Mucosal fluid transfer (ml/g wet wt/h)
Mucosal Na+ transfer (pieq/g wet wt/h)
control (5) 1.0 mg PRL (4)
0.99 ± 0.08 1.59 ± 0.12**
107.9 ± 16.9 214.0 ± 26.1**
control (5) 2.0 mg PRL (4)
0.52 ± 0.04*** 0.47 ± 0.05***
92.0 ± 9.4 84.5 ± 11.4
control (6) 1.0 mg PRL (6)
0.20 ± 0.02*** 0.24 ± 0.02***
23.9 ± 3.1*** 27.4 ± 2.6***
control (4) 1.0 mg PRL (4)
0.69 ± 0.07* 0.69 ± 0.09*
83.8 ± 7.9 77.1 ± 8.3
Ouabain (1 x 10~ 4 M)
control (4) 1.0 mg PRL (4)
0.46 ± 0.09** 0.49 ± 0.09**
20.4 ± 8.6** 15.8 ± 9.0**
Na-free Ringer .
control (4) 1.0 mg PRL (4)
0.19 ± 0.06*** 0.15 ± 0.02***
Incubation condition Normal Ringer (145 meq/liter Na+) Normal Ringer (glucose absent) Phlorizin (2 x 10"4 M) Choline chloride-Ringer (28 meq/liter Na+)
* 0.05 > P > 0.01; ** 0.01 > P > 0.001; *** P < 0.001, as compared with normal Ringer control values.
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PROLACTIN AND INTESTINAL ABSORPTION
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jejunum and ileum are also capable of active calcium transport especially under conditions of low calcium intake (23). Furthermore, Finkelstein and Schachter (24) showed that bovine growth hormone and to a less extent ovine prolactin stimulated active absorption of calcium by hypophysectomized rat duodenum in vivo. Evidence is presented herein showing that prolactin treatment significantly stimulates calcium absorption by the rat jejunum. The data obtained in the present experiments indicate that although prolactin may enhance magnesium absorption, the effect rarely reaches significant levels. The mechanism(s) by which prolactin stimulates fluid and ion absorption is uncertain. Also intriguing is the failure of larger doses of prolactin to stimulate intestinal absorption (the 2 and 4 mg daily doses are presumably "supraphysiological"). Angiotensin had been shown to stimulate sodium and water transport at low concentrations and to inhibit at higher concentrations (25). It is possible that prolactin has a biphasic action on jejunal fluid and sodium transport similar to that of angiotensin. Another explanation lies in the possible contamination of prolactin with vasopressin. In the rat and man (26, 27) administration of vasopressin inhibited water and NaCl absorption by the jejunum and ileum in vivo and in some instances resulted in net salt and water secretion. Conversely, vasopressin stimulates fluid and sodium transport in the rat colon (25) and mouse colon (28), an action evidently mediated by cyclic adenosine monophosphate. Because vasopressin antagonized the effects of prolactin on jejunal absorption, it is conceivable that its possible presence as a contaminant could account for the lack of effect of larger doses of prolactin. It is generally known that ouabain inhibits sodium transport, whereas phlorizin inhibits glucose transport and, at higher doses, metabolism (29). The low rates of Although maximal active calcium trans- fluid and sodium absorption observed in port occurs in the duodenum, the rat glucose-free Ringer or in the presence of
18) and man (6). Furthermore, ovine prolactin has been shown to stimulate fluid transport in the rat jejunum, an effect which is independent of the adrenal and the renin-angiotensin system (12). The results of the present study indicate that ovine prolactin is not only highly effective in stimulating fluid and sodium absorption by the rat jejunum, but also significantly enhances mucosal transfer of chloride, potassium and calcium and occasionally magnesium. Though reports on the effect of hypophysectomy on intestinal absorption are inconclusive (10), Righetti and Levitan (19) have shown that water, salt and glucose absorption in vivo is decreased by 50% following hypophysectomy. The results presented herein also demonstrated that hypophysectomy caused a significant decrease in mucosal fluid and sodium transport and that optimal doses of ovine prolactin restored absorption in most segments to normal levels. In the intact and hypophysectomized rats, prolactin action on fluid and sodium absorption showed a dose-related tendency, especially in the midjejunal segments (III and IV) in some experiments. In the jejunum, chloride absorption does not appear to be related to sodium transport in any simple fashion. Prolactin, however, augments chloride absorption especially in the more proximal and distal jejunal segments. The observations of Tidball (20) and Taylor et al. (21) that the jejunum sometimes actively secretes chloride into the lumen could explain why prolactin did not stimulate consistently and significantly chloride absorption in segment IV. Compared with other ions, potassium absorption has received relatively little attention. There are indications that in the intestinal mucosa sodium and potassium transport mechanisms may be linked (22). As shown in this study, the jejunum from prolactin-injected rats showed a significant increase in mucosal potassium transport.
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Endo • 1975 Vol 96 • No 5
MAINOYA
phlorizin indicated that the facilitatory actions of prolactin on jejunal transport are glucose-dependent. However, absence of glucose from the medium only slightly decreased the basal level of fluid and sodium transport but completely abolished the prolactin-stimulated transport. Much of this basal transport level could be sustained by endogenous glucose in the gut tissue (29). Basal fluid and sodium transport is further decreased by phlorizin possibly because it inhibits glucose-dependent transport and the glycolytic breakdown of glucose which in the jejunum provides energy for the transport of other solutes (11,29,30). When the sacs were incubated in Ringer containing low mucosal sodium concentration or in the presence of ouabain, an inhibition of fluid transport was also observed. These observations are in agreement with the hypothesis that sodium and glucose transport are interdependent and that water transport is dependent on solute transport (30). In any case, the present data demonstrate that prolactin administration effectively stimulates mechanism(s) involved in the regulation of fluid and ion movement across the intestinal mucosa. It is further suggested that prolactin may enhance fluid and ion absorption by stimulating active sodium transport. Of importance in osmoregulation is the ability to conserve water and ions when needed; this makes the regulation of fluid and salt transport by the mammalian intestine desirable in situations such as dehydration, gestation and lactation. In the last two circumstances, at least, high blood prolactin (including placental lactogen) levels would be expected to play a significant physiological role (cf. 31). Acknowledgments Aided by NIH Grant CA-05388 and a Rockefeller Foundation Fellowship. I am grateful to Professor Howard A. Bern for his support and guidance throughout this study and for his valuable criticism of the manuscript. oPRL generously provided by NIAMDD.
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