The mechanism by which angiotensin II (AII) exerts its pressor effect was examined in a saltwater teleost and elasmobranch. In vivo application of AII failed to elicit any changes in dogfish (Squalus acanthias) mesenteric microcirculatory blood flow, but the sculpin (Myoxocephalus octodecimspinosus) mesentery bed showed consistent reversible decreases in blood flow following AII application. Topical treatment with 0.5 mg phentolamine did not attenuate the AII response. In vitro addition of AII did not alter the mean resting tension of the dogfish celiac artery or intestinal vein, but significantly contracted the sculpin aorta. Addition of chromaffin tissue to the dogfish arterial muscle bath imparted significant vasoaction to AII when compared to saline. Both in vivo and in vitro experiments demonstrate the absence of functional AII vascular receptors in dogfish and their presence in the sculpin. Additional evidence for the mediation of AII vascular action in the dogfish by catecholamine release has been demonstrated.
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