THE ROLE OF ANGIOTENSIN IN ARTERIAL BLOOD-PRESSURE REGULATION IN THE TOAD BUFO-MARINUS

Little is known about the role of the renin-angiotensin system in anur an amphibians, although they appear to possess the functional componen ts of such a system. We investigated the role of angiotensin (ANG) in arterial blood pressure regulation in the conscious toad Bufo marinus using the angiotensin-converting enzyme blocker captopril, We found th at conversion of endogenous ANG I to ANG II made a significant contrib ution to mean arterial pressure in undisturbed animals. The vascular t one contributed by ANG II was not mediated via alpha adrenergic mechan isms because increases in pressure in response to ANG infusion were un affected by the presence of the alpha antagonist phentolamine. Angiote nsin-induced vasoconstriction was shown to be an important mechanism i n arterial blood pressure regulation in the face of an acute hypotensi ve perturbation of pressure brought about by sodium nitroprusside, Blo ckade of the conversion of ANG I to ANG II significantly delayed the r ecovery of mean arterial pressure after sodium nitroprusside-induced h ypotension. This suggests that the renin-angiotensin system may play a n important role in the initial responses to hypotension in anurans, w hether brought about by haemorrhage or dehydration.