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

Abstract

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.

Prolactin promotes oxytocin and vasopressin release by activating neuronal nitric oxide synthase in the supraoptic and paraventricular nuclei

“…By inducing the systemic release of OXT and AVP, PRL could modulate its own central inhibitory effect, helping to adjust the activation of the HPA axis to physiological demands. Likewise, the three hormones are released in response to osmotic stimulation (12,27). AVP is a major enhancer of water retention and blood pressure, OXT is a potent natriuretic factor, and PRL promotes sodium and water retention, as well as vasoconstriction (12,19,37).…”

Hydration as a limiting factor in lactation

“…Given these potentially important actions, the naturally high circulating levels of PRL produced during lactation may play a subsidiary role in maintaining water and/or electrolyte balance, particularly for women living in hot ambient temperatures. Kaufman and MacKay (1983) and Kaufman et al (1981) argue that PRL is responsible for the dipsogenic effect of lactation. More research, however, is needed in this area.…”

Branched-chain amino acid supplementation and human performance when hypohydrated in the heat

“…dehydration; central fatigue; serotonin; prolactin; mood THERE IS EVIDENCE THAT heat stress (25,27) and hypohydration (8,23) can independently impair performance through central nervous system (CNS) alterations (central fatigue) that may be serotonergic in origin (15,28,30,31,37). Common anatomic regions of the midbrain sensitive to temperature (9) and osmotic changes (15,31) are regulated, in part, by the serotonergic system. Stimulation of these regions results in prolactin (Prl) release from the pituitary, and pharmacological probes of serotonin (5-HT) regulation support the use of peripheral Prl concentrations as a surrogate index of brain 5-HT activity (45).…”