Neurohypophysial hormone secretion in hyperprolactinaemic women.

Prolactin (PRL) has been reported to promote antidiuresis and increase intestinal water-electrolyte absorption, whereas osmolar changes have been shown to influence PRL secretion. However, the mechanisms of action of PRL on the salt-water balance remain unclarified. The present clinical study targeted the effects of hyperprolactinaemia on the secretion of arginine-8-vasopressin (AVP), oxytocin (OXT) and cortisol. Plasma AVP and OXT were measured by radioimmunoassay, and cortisol by fluorimetry. In healthy women (21-39 y, n=6), an oral water load (OWL, 20 ml/bw) significantly suppressed the plasma levels of AVP, OXT and cortisol, and the PRL level too tended to decrease. In hyperprolactinaemic females (22-41 y, n=6, three with pituitary adenomas), water retention was registered following an OWL, together with paradoxical AVP and OXT level increases, whereas the cortisol response remained normal, and the PRL level did not change at all. Histamine (0.5 mg sc) stimulated the release of AVP, OXT and cortisol in the control and hyperprolactinaemic groups alike. These data suggest that alterations in AVP and OXT hypersecretion may contribute to the water retention in hyperprolactinaemia.