The renin-angiotensin system and vascular and dipsogenic regulation in elasmobranchs

The role of a renin-angiotensin-like system (RAS) in the regulation of blood pressure and drinking has been investigated in the elasmobranch, Scyliorhinus canicula. Injection of exogenous angiotensin II produced, as expected, a vasopressor response, though injection of the converting enzyme inhibitor, Captopril, alone produced little change in resting blood pressure. Papaverine, a smooth muscle relaxant, reduced blood pressure which completely recovered within 30 min. A subsequent injection of Captopril produced a rapid vasodepressor response with no recovery over 2 hr. The low basal levels of drinking in dogfish were not altered by Captopril injection but angiotensin II-induced increased drinking and papaverine administration resulted in markedly stimulated water intake, which was inhibited by coadministration with Captopril. Captopril inhibition of the recovery in blood pressure and associated dipsogenic response following the papaverine-induced hypotension is consistent with the activation of a RAS-like system in the dogfish. This and other evidence supporting the presence of a RAS-like system in elasmobranchs are discussed in relation to other vertebrates.