ANGIOTENSIN-II INDUCES WATER-ABSORPTION BEHAVIOR IN 2 SPECIES OF DESERT ANURANS

The octapeptide, angiotensin II (A-II), induces drinking behavior in s everal vertebrate species; however, relatively little is understood ab out A-II-induced thirst in amphibians. Scaphiopus couchii and Bufo cog natus were dehydrated to 90% of their ad libitum weight. This level of dehydration was sufficient to induce water absorption response (WR) b ehavior in both species. Fully hydrated toads injected intraperitoneal ly with A-II exhibited a significant amount of WR behavior. The minimu m effective dose for inducing WR behavior was 10 mu g/100 g-animal for S. couchii and 100 mu g/100 g-animal for B. cognatus. When dehydrated toads were treated with the A-II receptor antagonist, Th-&-saralasin, S. couchii, exhibited a significant increase in WR behavior, while B. cognatus did not respond behaviorally. Finally, treatment of dehydrat ed toads with captopril, a compound that inhibits conversion of angiot ensin I to A-II, did not significantly affect WR behavior in either sp ecies. These results support other findings that A-II may be involved in WR behavior in amphibians. However, the failure of Thr(2)-saralasin or captopril to inhibit WR behavior in dehydrated toads suggests that the receptor mechanisms involved in thirst regulation in toads may be different from those in mammals, and the renin-angiotensin system may not be the only potential mediator of WR behavior in these species. ( C) 1994 Academic Press, Inc.