Angiotensin II Responses of Rabbit Aortic Strips Compared with Fast and Slow Epinephrine Responses 1

Abstract

Summary

Epinephrine causes a biphasic contraction of rabbit aorta, consisting of (i) a fast component, F, ascribed to release of intracellular calcium, and (ii) a slow component, S, ascribed to calcium movement into the muscle cell. Angiotensin produces a single-phase contraction of uncertain calcium source. Insight into the latter might be gained if angiotensin contractions consistently resembled the F or S epinephrine response. Contractions of rabbit aorta strips produced by both drugs were therefore compared during five interventions which had dissociated effects on F or S epinephrine responses. These interventions consistently altered the angiotensin responses in the same way as they affected epinephrine F responses, and differently from their effects on epinephrine S responses. These results are compatible with the view that the likely major source of activator calcium for angi-otensin-induced contractions of rabbit aorta is intracellular, although a small extracellular calcium contribution could not be excluded.