Tachyphylaxis to Alpha- and Beta-Angiotensin in Dogs Perfused with Ringer's Solution or Blood

Repeated injections of µ-asparaginyl-angiotensin in the hindquarters of dogs perfused either with blood or with Ringer's solution did not lead to tachyphylaxis with doses of less than 0.5 µg. Above this dose tachyphylaxis developed in preparations perfused with Ringer's solution. Tachyphylaxis occurred in blood-perfused preparations at doses of 2 µg and above. Tachyphylaxis to β-aspartyl-angiotensin appeared with doses above 0.5 µg irrespective of the perfusing medium used. It is concluded that plasma angiotensinase activity plays some part in limiting the development of techyphylaxis only to µ-asparaginyl-angiotensin; also, that removal of angiotensin from the biophase is dependent in part on the angiotensin being removed by perfusion. A dynamic model for the action of angiotensin on its receptor is proposed.