Vasopressin contamination as a cause of some apparent renal actions of prolactin

SUMMARY1. Ouabain-sensitive 80Rb+ uptake in slices of lactating rabbit mammary gland significantly increased after 20 min or 1 hr of incubation with ovine prolactin (NIH-P-S12; 1 ,ug/ml.).2. Total K+ content of the tissue significantly increased at 20 min of incubation with prolactin.3. Neither vasopressin nor oxytocin, at concentrations of 2, 20 or 40 #i.u./ml., had a significant effect on ouabain-sensitive 86Rb+ uptake or total K+ of the tissue after 30 min or 1 hr of incubation.4. Tissue slices incubated in cycloheximide at 10 ,ug/ml. for up to 260 min showed a reduction in ouabain-sensitive 86Rb+ uptake and total K+ content, with half-lives of 115 and 63 min, respectively. 5. No consistent in vitro effect of prolactin on (Na+ +K+) -activated ATPase activity in homogenates, crude microsomal fractions or Nal-activated membrane fractions from lactating rabbit mammary gland was found.6. After 3 hr of incubation of tissue slices in the presence or absence of prolactin (5 ,sg/ml.), no significant differences in the number of [G_-3H]ouabain molecules bound per cell (5'2 x 104 and 6-2 x 104, respectively) or in the dissociation constant (KD) for ouabain binding (5 4 x 10-7 M and 5.9 X 10-7 M, respectively) were observed. 7. Incubation of the tissue with cycloheximide (10 jug/ml.) for 1-6 hr caused an exponential decrease in [G-3H]ouabain binding with a half-life of 3 hr.8. It is concluded that prolactin stimulates the activity ofthe (Na+ + K+)-activated ATPase in slices of lactating rabbit mammary gland within one hour but over this period does not affect the number of ouabain-binding sites, which are apparently turned over with a half-life of 1-3 hr.

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Effect of prolactin on 86Rb+ uptake, potassium content and [G‐3H]ouabain binding of lactating rabbit mammary tissue.

Falconer¹,

Langley²,

Vácek³

1983

“…The evidence that injected prolactin does influence water and electrolyte excretion is controversial especially since it has been found that some of the preparations of prolactin are contaminated with vasopressin (Vorherr, Vorherr & Solomon, 1978). Thus Keeler & Wilson (1976) and Carey, Johanson & Seit (1977) found that, when vasopressin-free prolactin was used, there was no evidence for antidiuretic activity and indeed El Karib & Green 1981) have shown that prolonged administration of prolactin injected s.c. can increase glomerular filtration rate. However, Kaufman, Mackay & Scott (1981) found that, although urine output was greater in rats bearing ectopic pituitary glands, this could be totally accounted for by their increased water intake.…”

Section: Discussionmentioning

confidence: 99%

Plasma prolactin levels and body fluid deficits in the rat: causal interactions and control of water intake.

Kaufman¹,

Mackay²

1983

SUMMARY1. A study was made of the responses of chronically hyperprolactinaemic rats to selected dipsogenic stimuli. Measurements were also made of the correlation between the state of hydration of the animal and the plasma prolactin levels.2. After 24 h water deprivation. s.c. isoprenaline (10 ,sg/kg body wt.) or i.P.injection (5 ml/kg body wt.) of a hypertonic solution (50 % w/w) of polyethylene glycol (mol. wt 20000) there was no difference between the hyperprolactinaemic and control rats with respect to the total water intake, the time course of drinking or the urine output. 3. After i.v. injection of 2 M-NaCl (5 ml/kg body wt.) there was no difference between the hyperprolactinaemic and control rats with respect to the total water intake or urine output. However, the hyperprolactinaemic rats drank more slowly than the controls.4. Whey angiotensin II was infused i.v. at a rate of 0-2 ,ug/min, the water intake was greater and the threshold to drinking lower in the hyperprolactinaemic than control rats.5. After 24 h water deprivation, plasma prolactin levels rose significantly in both the control and hyperprolactinaemic rats. When the rats were injected i.v. with hypertonic saline (5 ml, 2 M-NaCl/kg body wt.) and denied access to water, plasma prolactin levels had not changed 1 h later in either the control or hyperprolactinaemic animals.6. It is concluded that there is no interaction either between the plasma osmolality and prolactin secretion or between the plasma prolactin levels and the amount of water drunk in response to intracellular fluid deficits. However, prolactin secretion is stimulated by the combined intra-and extracellular deficits resulting from water deprivation and there is a clearly demonstrated interaction between prolactin and the extracellularly mediated stimulus of angiotensin II.

“…Some prolactin preparations (produced mainly by the U.S. National Institute of Health) are contaminated with vasopressin (Vorherr, Vorherr & Solomon, 1977;Keeler & Wilson, 1976). However, the Sigma prolactin used in the present study contains very little vasopressin (2-5 ng vasopressin/mg prolactin; Keeler & Wilson, 1976), and this cannot account for its antidiuretic activity (Miller & Van Gemert, 1976). Using Keeler & Wilson's reported level of vasopressin contamination the rate of prolactin administration employed in the present study (7-1 ,g (100 g body wt.)-'.…”

Section: Discussionmentioning

confidence: 99%

“…A problem in the interpretation of many previous reports (e.g. Keeler & Wilson, 1976) is the extremely high doses of prolactin which have been employed. In the present experiments, the dose of prolactin used was calculated to produce a plasma level close to the maximum physiological concentration in the female rat (Lucci et al 1975).…”

Section: Introductionmentioning

confidence: 99%

Effect of prolactin on urinary excretion and renal haemodynamics in conscious rats.

Bliss¹,

Lote²

1982

SUMMARY1. Conscious rats received a saline infusion (5-8 ml. hr-') via a tail vein, for a 6 hr period. For the final 2 hr of this infusion period, prolactin (74 ,tg (100 g body wt.)-'. hr-1) was incorporated in the infusate. A control group of animals continued to receive saline alone.2. In the first hour of prolactin administration (in comparison with the control group), urine flow, sodium output and osmolal output were all significantly reduced (P < 0-02); there was also a reduction (P < 0-05) in renal plasma flow (p-aminohippurate clearance), but the filtration fraction did not alter. The changes in urinary excretion, and in renal haemodynamics, did not persist for the second hour of prolactin adminstration, but there was a sustained increase in body fluid volume.3. It is possible that altered renal haemodynamics are responsible for the reduced urinary water and solute excretion which occurs during acute prolactin administration.