EFFECT OF DUP-753, A NONPEPTIDE ANGIOTENSIN-II RECEPTOR ANTAGONIST, ON THE DRINKING RESPONSES TO ACUTELY ADMINISTERED DIPSOGENIC AGENTS IN RATS

The present studies examine the effect of the nonpeptide angiotensin II (AII) type 1 receptor antagonist, DuP 753, on water intake in rats treated with dipsogenic stimuli, which are thought to induce drinking via release of renin and subsequent formation of All. Subcutaneous administration of DuP 753 in doses that are known to inhibit drinking induced by AII failed to inhibit the water intake of rats following subcutaneous administration of the beta-adrenoceptor agonist isoproterenol. The peptide antagonist 1Sar, 8Ileu-AII, which blocks both AII type 1 and AII type 2 receptors, also failed to inhibit isoproterenol-induced drinking, suggesting that neither subtype is involved in this drinking response. Additional studies verified previous reports that acute subcutaneous administration of both the beta-adrenoceptor antagonist propranolol and the angiotensin I-converting enzyme inhibitor captopril could block the drinking response to subcutaneous administration of isoproterenol. Subcutaneous administration of DuP 753 also failed to inhibit the drinking responses to subcutaneous administration of serotonin, 5-hydroxy-tryptophan, hypertonic saline, and polyethylene glycol. However, central intraventricular administration of DuP 753 inhibited the drinking response to subcutaneous administration of isoproterenol. The results are discussed in terms of the importance of AII in mediating isoproterenol-, serotonin-, and 5-hydroxytryptophan-induced water intake and suggest a need to readdress this mechanism.