Specificity of Angiotensin Antagonists in the Mesenteric Vasculature of Dogs 1 2

Abstract

Abstract

Experiments were conducted to assess whether the octapeptide antagonist Sar¹-Ile⁸-angiotensin II or the heptapeptide antagonist Ile⁷-angiotensin III demonstrates specificity for antagonizing the mesenteric vasoconstrictor properties of angiotensin II or angiotensin III. Experiments were performed on 12 dogs anesthetized with sodium pen-tobarbital. In all dogs, the effects of five graded doses (10, 20, 40, 80, and 160 pmole, bolus injections) of angiotensin II and angiotensin III on superior mesenteric artery blood flow were tested. At all doses tested, angiotensin II was more potent than angiotensin III. Administration of the middle dose (40 pmole) of angiotensin II and angiotensin III was repeated during the infusion of either Ile⁷-angiotensin III (N = 6) or Sar¹-Ile⁸-angiotensin II (N = 6) at five different dosages into the superior mesenteric artery, Sar¹-Ele⁸-angiotensin II antagonized equally the mesenteric vasoconstrictor effects of both angiotensin II and angiotensin III. Ile⁷-angiotensin III was not absolutely specific as an antagonist of the mesenteric vasoconstrictor effects of angiotensin III.