Effect of Intracerebroventricularly Administered Octopamines and Synephrines on Angiotensin 2-Induced Water Intake in Rats

Recent studies from this laboratory showed that l-m-synephrine (phenylephrine), a metabolite of l-m-octapamine, inhibited the drinking response of rats to peripherally administered angiotensin 2. The objective of this investigation was to determine whether the isomers ofboth octapamine and synephrine could inhibit angiotensin 2-induced dipsogenesis in the rat. Of the isomers tested, only d,l-m-octopamine and l-m-synephrine blocked the dipsogenic response to administration of angiotensin 2 (200 micrograms/kg, SC). The antidipsogenic effect of both d,l-m-octopamine and l-m-synephrine could be blocked by concurrent administration of yohimbine (300 micrograms/kg, IP), an alpha(sub 2)-adrenoceptor antagonist. The results indicate that m-octopamine and m-synephrine exert their antidipsogenic effect via alpha(sub 2)-adrenoceptors. These studies add to a growing body of data suggesting that activation of alpha(sub 2)-adrenoceptors inhibits, while blockade of these receptors enhances, angiotensin 2-induced drinking.