Central interactions between angiotensin II and PGD sub(2) in the regulation of vasopressin and oxytocin secretion in dehydrated rats

• Published in: Brain research 2001-01, Vol.889 (1-2), p.84-88
• Main Authors: Kadekaro, M, Terrell, M L, Bui, V, Summy-Long, J Y
• Format: Article
• Language: English
• Subjects: prostaglandin D2
• ISSN: 0006-8993

Brain-derived angiotensin II (ANG II) and prostaglandins have important roles in the regulation of body fluid and blood pressure homeostasis. In the present studies we investigated the central interactions between these two neurochemical products in regulating the hypothalamo-neurohypophysial system during dehydration. Intracerebroventricular (icv) administration of prostaglandin D sub(2) (PGD sub(2); 20 mu g/5 mu l) to conscious adult male Sprague-Dawley rats deprived of water for 24 h did not alter significantly the already elevated plasma levels of vasopressin or oxytocin. When PGD sub(2) was administered in combination with losartan, an antagonist of ANG II AT sub(1)-receptor subtype, however, concentrations of both hormones in plasma became further elevated. Icv administration of ANG II (50 ng/5 mu l) increased further the enhanced plasma levels of vasopressin and oxytocin, as expected. Pretreatment with indomethacin (200 mu g/5 mu l; icv), an inhibitor of cyclo-oxygenase, significantly attenuated the ANG II-induced increase in oxytocin secretion only. Independent of the presence of ANG II, however, indomethacin decreased plasma levels of vasopressin, but not oxytocin. These results indicate that a prostaglandin is required for the stimulated release of vasopressin during dehydration and that the elevation of oxytocin secretion in response to ANG II depends largely on activation of cyclo-oxygenase and production of prostaglandins. The oxytocin response to exogenously administered PGD sub(2), however, can be negatively modulated by a mechanism dependent upon ANG II AT sub(1) receptors.