PROLACTIN, DIURETICS AND URINARY ELECTROLYTES IN NORMAL SUBJECTS
R. AUTY, *
t
R. A. BRANCH, E. N. COLE, D. LEVINE L. RAMSAY
AND
Departments of Medicine and Pharmacology, University of Bristol, Avon,
Tenovus Institute for Cancer Research, Cardiff and % Division of Scientific G. D. Searle and Co. Ltd, High Wycombe, Bucks.
Affairs,
(Received 29 August 1975) SUMMARY
relationship of plasma prolactin concentration and renal electrolyte excretion has been investigated in six normal male volunteers. In two studies, 80 mg frusemide were administered at 18.00 h on Day 1 and followed by dietary sodium restriction. In study A, after 38 h of sodium depletion, a second dose of frusemide was administered at 08.00 h on Day 3. In study B, after 14 h of sodium depletion, the effect of administration of 100 mg spironolactone or 45 mg prorenoate potassium (another aldosterone antagonist) at 08.00 h on Day 2 was compared with that of a placebo. The
After the first dose of frusemide in study A, the mean plasma prolactin concentration correlated negatively with the urinary Na and K excretion over 5 h. After 38 h sodium depletion, the plasma prolactin concentration correlated positively with urinary Na excretion following the second dose of frusemide. In study B, after Na depletion for 14 h the plasma prolactin concentration at 08.00 h on Day 2 had a positive correlation with the 24 h urinary log10 Na:K ratio following placebo administration and had negative correlations with the true urinary log10 Na:K ratio following spironolactone and prorenoate potassium administration. Neither acute Na deprivation nor the administration of single doses of frusemide, spironolactone or prorenoate potassium appeared to affect the normal circadian rhythm of plasma prolactin concentrations which remained constant for each subject throughout the 3 months covered by the investigation. The correlations of plasma prolactin concentration to renal excretion of electrolytes, with no evidence for a negative feedback control mechanism, suggest an indirect relationship between prolactin and renal function. introduction
It has recently been suggested that prolactin may have a physiological role in Na and homeostasis. Administration of prolactin from various species to rat and man produces Na retention (Lockett & Nail, 1965; Horrobin, Lloyd, Lipton, Burstyn, Durkin & Muiruri, 1971) and prolonged Na deprivation in rats is associated with an increase in pituitary and plasma prolactin concentrations (Relkin & Adachi, 1973). In normal subjects, there is a circadian rhythm of prolactin concentration with highest levels overnight, when Na § Present address : Ahmado Bello University Hospital, Zaria, Nigeria. || Present address and address for reprints: Division of Clinical Pharmacology, Vanderbilt University, Nashville, Tennessee 37232, U.S.A.
retention is maximal, and lowest levels during the day, when more Na is excreted (Nokin, Vekemans, L'Hermite & Robyn, 1972; Simpson, Cole, Hume, Fleming & Travadia, 1975). However, the relationship between concentration of endogenous prolactin and renal excre¬ tion of Na and has not been examined in man. If prolactin has a physiological role, then variation in the prolactin concentration might explain inter-subject variation in electrolyte excretion, and acute changes in electrolyte status might influence prolactin concentration by a negative feedback control. Therefore it was of interest to study these factors in a series of acute experiments with diuretics in man. SUBJECTS AND METHODS
Six normal healthy male volunteers (aged 20-25 years) consented to take part in two studies, which had been approved by an ethical committee. The investigation was performed within a period of 3 months.
Experimental procedures
Study A
The effects of frusemide were examined in normal subjects in an unstressed situation and then after sodium deprivation. Frusemide (80 mg) was administered orally at 18.00 h on Day 1. Sodium depletion was maintained for 43 h by a 20 mmol Na, 160 mmol diet. Free water intake was allowed. Blood and urine samples were taken at 15 min intervals for 1-5 h, then every 30 min until 3 h after frusemide administration and hourly for a further 2 h. On Day 2, urine was collected 2 hourly from 08.00 h. This was followed by an 8 h overnight collection. On Day 3, 38 h after the first dose, frusemide (80 mg) was administered orally at 08.00 h. Blood and urine samples were collected at 15 min intervals for 2 h then hourly for 3 h.
Study The effects of a single dose of spironolactone, prorenoate potassium or placebo were examined in Na-depleted subjects. In each of the three trials 80 mg frusemide were admin¬ istered orally at 18.00 h on Day 1. Sodium depletion was then maintained by a 20 mmol sodium, 160 mmol potassium diet over the next 38 h. Free water intake was allowed. At 08.00 h on Day 2, 14 h after frusemide administration, spironolactone (100 mg), prorenoate potassium (45 mg) or placebo were administered in a randomized, cross-over, double-blind latin square design. Urine samples were then collected 2 hourly for 16 h, followed by a final 8 h overnight urine collection. Venous blood samples for determination of prolactin concentration were taken at 18.00 and 23.00 h on Day 1, 08.00, 12.00 and 18.00 h on Day 2 and 08.00 h on Day 3.
Analysis
measured by radioimmunoassay (Cole & Boyns, 1973). Results prolactin are expressed as milliunits of MRC Research Standard A 71/222/ml where 1 mu. is equiva¬ lent to 50 ng highly purified prolactin. Displacement of 10 % of bound radioiodinated pro¬ lactin was achieved by 008 mu. of standard hormone/ml. Intra-assay coefficients of variation were less than 10 % and inter-assay variations less than 12 %. Sodium and potassium in the urine were measured by flame photometry. Plasma
was
RESULTS
The relationship of plasma prolactin to electrolyte excretion after frusemide (Study A) The mean plasma prolactin concentration measured during the 5 h periods following two administrations of frusemide was compared with the total Na and excretion in the urine
the same two periods (Table 1). After the initial dose of frusemide there were negative correlations between plasma prolactin concentration and Na excretion (r < —0-804, 0-054) and excretion (r -0-81, < 0-05) (Fig. 1). Following the second dose of frusemide at 08.00 h on Day 3, the relationship between plasma prolactin concentration and Na excretion was inverted (r +0-83, < 005) (Fig. 1). There was no significant correlation with excretion. over
=
=
=
Table 1. Comparison of mean plasma prolactin concentration and the diuretic response during the 5 h following oral administration of 80 mg frusemide to six normal male subjects
(First dose administered at 18.00 h on Day 1 ; the second dose administered at 08.00 h after 38 h of sodium deprivation (means ± s.e.m.).) 1st dose of frusemide 2nd dose of frusemide
Prolactin concentration (mu./ml) Sodium excretion (mmol) Potassium excretion (mmol) Na:K ratio
o
|
ß o
1 g | ej
'35
1
on
Day 3
(Day 1)
(Day 3)
(Student's paired /-test)
0-108 ±0-055 203 + 24 48 ±19 4-6 + 1-3
0-112 ±0-051 128 ±24 50+11 2-6 + 0-49
NS
R. AUTY, *
t
R. A. BRANCH, E. N. COLE, D. LEVINE L. RAMSAY
AND
Departments of Medicine and Pharmacology, University of Bristol, Avon,
Tenovus Institute for Cancer Research, Cardiff and % Division of Scientific G. D. Searle and Co. Ltd, High Wycombe, Bucks.
Affairs,
(Received 29 August 1975) SUMMARY
relationship of plasma prolactin concentration and renal electrolyte excretion has been investigated in six normal male volunteers. In two studies, 80 mg frusemide were administered at 18.00 h on Day 1 and followed by dietary sodium restriction. In study A, after 38 h of sodium depletion, a second dose of frusemide was administered at 08.00 h on Day 3. In study B, after 14 h of sodium depletion, the effect of administration of 100 mg spironolactone or 45 mg prorenoate potassium (another aldosterone antagonist) at 08.00 h on Day 2 was compared with that of a placebo. The
After the first dose of frusemide in study A, the mean plasma prolactin concentration correlated negatively with the urinary Na and K excretion over 5 h. After 38 h sodium depletion, the plasma prolactin concentration correlated positively with urinary Na excretion following the second dose of frusemide. In study B, after Na depletion for 14 h the plasma prolactin concentration at 08.00 h on Day 2 had a positive correlation with the 24 h urinary log10 Na:K ratio following placebo administration and had negative correlations with the true urinary log10 Na:K ratio following spironolactone and prorenoate potassium administration. Neither acute Na deprivation nor the administration of single doses of frusemide, spironolactone or prorenoate potassium appeared to affect the normal circadian rhythm of plasma prolactin concentrations which remained constant for each subject throughout the 3 months covered by the investigation. The correlations of plasma prolactin concentration to renal excretion of electrolytes, with no evidence for a negative feedback control mechanism, suggest an indirect relationship between prolactin and renal function. introduction
It has recently been suggested that prolactin may have a physiological role in Na and homeostasis. Administration of prolactin from various species to rat and man produces Na retention (Lockett & Nail, 1965; Horrobin, Lloyd, Lipton, Burstyn, Durkin & Muiruri, 1971) and prolonged Na deprivation in rats is associated with an increase in pituitary and plasma prolactin concentrations (Relkin & Adachi, 1973). In normal subjects, there is a circadian rhythm of prolactin concentration with highest levels overnight, when Na § Present address : Ahmado Bello University Hospital, Zaria, Nigeria. || Present address and address for reprints: Division of Clinical Pharmacology, Vanderbilt University, Nashville, Tennessee 37232, U.S.A.
retention is maximal, and lowest levels during the day, when more Na is excreted (Nokin, Vekemans, L'Hermite & Robyn, 1972; Simpson, Cole, Hume, Fleming & Travadia, 1975). However, the relationship between concentration of endogenous prolactin and renal excre¬ tion of Na and has not been examined in man. If prolactin has a physiological role, then variation in the prolactin concentration might explain inter-subject variation in electrolyte excretion, and acute changes in electrolyte status might influence prolactin concentration by a negative feedback control. Therefore it was of interest to study these factors in a series of acute experiments with diuretics in man. SUBJECTS AND METHODS
Six normal healthy male volunteers (aged 20-25 years) consented to take part in two studies, which had been approved by an ethical committee. The investigation was performed within a period of 3 months.
Experimental procedures
Study A
The effects of frusemide were examined in normal subjects in an unstressed situation and then after sodium deprivation. Frusemide (80 mg) was administered orally at 18.00 h on Day 1. Sodium depletion was maintained for 43 h by a 20 mmol Na, 160 mmol diet. Free water intake was allowed. Blood and urine samples were taken at 15 min intervals for 1-5 h, then every 30 min until 3 h after frusemide administration and hourly for a further 2 h. On Day 2, urine was collected 2 hourly from 08.00 h. This was followed by an 8 h overnight collection. On Day 3, 38 h after the first dose, frusemide (80 mg) was administered orally at 08.00 h. Blood and urine samples were collected at 15 min intervals for 2 h then hourly for 3 h.
Study The effects of a single dose of spironolactone, prorenoate potassium or placebo were examined in Na-depleted subjects. In each of the three trials 80 mg frusemide were admin¬ istered orally at 18.00 h on Day 1. Sodium depletion was then maintained by a 20 mmol sodium, 160 mmol potassium diet over the next 38 h. Free water intake was allowed. At 08.00 h on Day 2, 14 h after frusemide administration, spironolactone (100 mg), prorenoate potassium (45 mg) or placebo were administered in a randomized, cross-over, double-blind latin square design. Urine samples were then collected 2 hourly for 16 h, followed by a final 8 h overnight urine collection. Venous blood samples for determination of prolactin concentration were taken at 18.00 and 23.00 h on Day 1, 08.00, 12.00 and 18.00 h on Day 2 and 08.00 h on Day 3.
Analysis
measured by radioimmunoassay (Cole & Boyns, 1973). Results prolactin are expressed as milliunits of MRC Research Standard A 71/222/ml where 1 mu. is equiva¬ lent to 50 ng highly purified prolactin. Displacement of 10 % of bound radioiodinated pro¬ lactin was achieved by 008 mu. of standard hormone/ml. Intra-assay coefficients of variation were less than 10 % and inter-assay variations less than 12 %. Sodium and potassium in the urine were measured by flame photometry. Plasma
was
RESULTS
The relationship of plasma prolactin to electrolyte excretion after frusemide (Study A) The mean plasma prolactin concentration measured during the 5 h periods following two administrations of frusemide was compared with the total Na and excretion in the urine
the same two periods (Table 1). After the initial dose of frusemide there were negative correlations between plasma prolactin concentration and Na excretion (r < —0-804, 0-054) and excretion (r -0-81, < 0-05) (Fig. 1). Following the second dose of frusemide at 08.00 h on Day 3, the relationship between plasma prolactin concentration and Na excretion was inverted (r +0-83, < 005) (Fig. 1). There was no significant correlation with excretion. over
=
=
=
Table 1. Comparison of mean plasma prolactin concentration and the diuretic response during the 5 h following oral administration of 80 mg frusemide to six normal male subjects
(First dose administered at 18.00 h on Day 1 ; the second dose administered at 08.00 h after 38 h of sodium deprivation (means ± s.e.m.).) 1st dose of frusemide 2nd dose of frusemide
Prolactin concentration (mu./ml) Sodium excretion (mmol) Potassium excretion (mmol) Na:K ratio
o
|
ß o
1 g | ej
'35
1
on
Day 3
(Day 1)
(Day 3)
(Student's paired /-test)
0-108 ±0-055 203 + 24 48 ±19 4-6 + 1-3
0-112 ±0-051 128 ±24 50+11 2-6 + 0-49
NS
