PROSTAGLANDINS

COMPARISON OF THE EFFECTS OF PROSTAGLANDINS D2, F2o AND El ON SPONTANEOUS CONTRACTIONS OF RABBIT OVIDUCT

Cheryl M. Heesch, Guillermo Valenzuela and Barrie J. Hodgson Center for Research and Training in Reproductive Biology and Voluntary Regulation of Fertility Departments of Obstetrics and Gynecology and Pharmacology The University of Texas Health Science Center at San Antonio 7703 Floyd Curl Drive San Antonio, Texas 78284

ABSTRACT The effects of PGD2, PGF and PGE were studied on the circular muscle of post-ovulatory rabbze oviduct: in vitro. PGEl inhibited spontaneous contractile activity. Lower concentrations of PGD2 and PGF2a were stimulatory andhigher concentrationswere inhibitory. Since PGD2 may be produced in the oviduct, any hypothesis concerning the role of prostaglandins in the control of oviductal motility and ovum transport should include PGD2 as well as PGFs and PGEs.

ACENOWLEIXXMENTS The authors thank Dr. John Pike, UpJohn Co. for gifts of prostaglandins. This work was supported by NIH HD-09339-02 and Rockefeller Foundation. G.V. is a Rockefeller Foundation Postdoctoral Fellow in Reproductive Biology.

INTRODUCTION Prostaglandin El (PGEl) relaxes and PGF20 contracts the rabbit oviduct -in vivo and -in vitro (1,2,3). PGD2 has been described as being 20-140 times more potent than PGF2, in some smooth muscle systems in vivo (4). Using an -in vitro prostaglandin synthetase system from the rabbit oviduct, a product has been isolated which has the same mobility as PGD2 in thin layer chromatography and which is present in the same amount as PGF20 and PGE (5). Horton and Jones (4) reported that PGD2 caused relaxation, sometimes preceded by a contraction, of rabbit oviduct -in vivo, but methodology and potency were not clearly defined. The present study was designed to quantitatively compare the effects of PGD2 with PGEl and PGF20 on spontaneous contractions of the circular musculature of the post-ovulatory rabbit oviduct -in vitro.

AUGUST 1977 VOL. 14 NO. 2

279

PROSTAGLANDINS

MATERIALS AND METHODS Thirteen mature New Zealand White female rabbits, maintained under standard housing conditions, were injected (i.v.) with 100 I.U. of Human Chorionic Gonadotropin (HCG) (Ayerst Lab.) one month prior to use. (This provides a standard animal which has passed through at least one pseudopregnancy). They were again injected with HCG 24 hours before they were killed with an overdose of sodium pentobarbital. Preliminary experiments have shown that there are no differences between spontaneous activity of oviductal smooth muscle obtained from animals killed by barbiturate overdose and animals killed by cervical dislocation (6). The oviducts were excised, trimmed free of fat, and segments (3 mm long) of the ampullary-isthmicjunction (AIJ) were mounted in isolated organ baths using stainless steel hooks passed through the lumen to record from the circularly oriented muscle fibers, as described previously (6). (AIJ was used because it consistently demonstrates spontaneous contractions 24 hours after HCG). Tissues were bathed in Tyrode's solution continuously gassed with 95% O2 and 5% CO2 and maintained at 370C. Isometric tension was measured with Statham (UC3) force tranducers and recorded on a Beckman Dynograph. After an equilibration period of 45 minutes, with 0.5 g initial tension, cumulative concentration-responsecurves were established by adding prostaglandin (PGF2,, PGEl or PGD2) every three minutes for final bath concentrations ranging from 2.8 x lo-*M to 1.1 x 10s4M. Area under the tension-time curve (2 minutes) was measured by planimetry before drug addition and after each concentration of prostaglandin. Results were expressed as percentage of control activity. The prostaglandins were dissolved in ethanol: distilled water (1:9) and subsequently diluted with distilled water. Each tissue was exposed to a maximum of 0.5% (by volume) of ethanol, a concentrationwhich was shown in a preliminary series of experiments to have no significant effect on spontaneous activity of the tissue preparation.

RESULTS Lower concentrations of PGD2 and PGF20 increased contractile activity of the ampullary-isthmicjunction whereas higher concentrationswere inhibitory (Fig. 1). Increased area under the curve was due to increased frequency and amplitude of contractions and baseline tension was unaltered. PGD2 was qualitatively similar to PGF2, but was less potent in inhibiting activity at high concentrations. Exposure to PGEl resulted in inhibition of the oviduct.

DISCUSSION Ova are thought to be moved through the oviduct by muscular contractions (7). The role of prostaglandins in the control of ovum transport is uncertain but has been considered in terms of an increase or decrease in the ratjo of PGFs to PGEs, resulting in changes in propulsive and frictional forces and retention of ova in the oviduct or passage into the uterus (2). However, the endoperoxide intermediates in PG synthesis

280

AUGUST 1977 VOL. 14 NO. 2

PROSTAGLANDINS

10-t

PG (M)

Fi.gure

1:

Concentration-responsecurves for contractile response of ovi(0) and PGE (A). ductal smooth muscle to PGD2 (O), PGF Each point represents the mean f Stanz" ard error of $he mean of 10 (PGD2) or 8 (PGF2, and PGE1) oviductal segments, except for the two lowest concentrations of PGD2 where n = 2. Ordinate: response to prostaglandin expressed as percentage of control activity (area under tension-time curve). Absicissa: molar concentration of prostaglandins.

from which PGE and PGF originate (PGG2 and PGH2) are also precursors for synthesis zf PGD2 (87. We have demonstrated that PGD2 is equipotent with PGF in stimulating oviductal circular musclebutless potent in nhibition at high concentrations. We used cumulative dose-response causing %a curves in this study because it seems likely that tissues -in vivo would be exposed to gradually changing concentrations of PGs. Although these doseresponse curves do not allow for correction for tachyphylaxis,which has been shown to occur in responses of oviduct to PGs (9), the maximum in the present study is similar to that stimulator-yconcentration of PGF reported by Conrad and Cnwudiwe t% who used single doses of PGs. Furthermore tachyphylaxis, defined as decreasing response to the same dose of agonist, cannot account for the reversal of the response to PGFza from stimulatory to inhibitory at higher doses.

AUGUST 1977 VOL. 14 NO. 2

281

PROSTAGLANDINS

Since it appears that PGD2 is produced in the oviduct, experiments in which oviductal prostaglandins are measured or hypotheses concerning the role of prostaglandins in the control of ovum transport should probably include the role of PGD2 as well as PGFs and PGEs.

REFERENCES 1.

Horton, E.W. and I.H.M. Main. A comparison of the actions of prostaglandins F2o and El on smooth muscle. Br. J. Pharmacol. 24:470, 1965.

2.

Spilman, C.H. and M.J.K. Harper. Effects of prostaglandins on oviduct motility in estrous rabbits. Biol. Reprod. 9:36, 1973.

3.

Conrad, J.R. and Onwudiwe. Dose-response effects of the prostaglandins PGEl and PGF2,, upon the isometric tension of segments of the ampulla, isthmus, and uterus of the estrous rabbit. Prostaglandins 4:47, 1973.

4.

Horton, E.W. and R.L. Jones. Biological activity of prostaglandin D2 on smooth muscle. Br. J. Phannacol. 52:llOP, 1974.

5.

Valenzuela. G. and M.J.K. Harper. Effect of estrogen on activity of prostaglandin synthetase in rabbit oviduct. Prostaglandins 12:535, 1976.

6.

Hodgson, B.J. and C.J. Pauerstein. The effect of ovulation on the response of the rabbit oviduct to adrenergic agonists -in vitro. Biol. Reprod. 10:346, 1974. Hodgson, B.J., A. Tale, and C.J. Pauerstein. Oviductal ovum surrogate movement: interrelation with muscular activity. Biol. Reprod. 16:394, 1977. Nugteren, D.H. and E. Hazelhof. Isolation and properties of intermediates in PG biosynthesis. Biochim. Biophys. Acta. 326:448, 1973. Heilman, R.D. and M. Strainer. Dose-response effects of prostaglandin F2o on the rabbit oviduct: reproductive endocrine influence and tachyphylaxis. Prostaglandins 12:127, 1976.

Received

282

5/18/77

- Approved

6/12/77

AUGUST 1977 VOL. 14 NO. 2

Comparison of the effects of prostaglandins D2, F2alpha and E1 on spontaneous contractions of rabbit oviduct.

PROSTAGLANDINS COMPARISON OF THE EFFECTS OF PROSTAGLANDINS D2, F2o AND El ON SPONTANEOUS CONTRACTIONS OF RABBIT OVIDUCT Cheryl M. Heesch, Guillermo...
198KB Sizes 0 Downloads 0 Views