The Interaction of Angiotensin II with other Spasmogens on Vascular Smooth Muscle

Abstract

The interaction of angiotensin II with exogenous and endogenous noradreneline was studied on isolated vascular tissues taken from the rabbit. Angiotensin II potentiated responses to nerve stimulation, but not to noredrenoline, when infused into the isolated ear artery, isolated whole ear and isolated mesenteric bed. However, contact of the polypeptide with the outer surface of the isolated ear artery induced a depression of responses to nerve stimulation. Angiotensin II and 5-HT at subthreshold concen­trations induced a non-specific increase in sensitivity of the rabbit isolated aorta. At contractor concen­trations, angiotensin II induced a non-specific depression of responses to vascular agonists. The polypeptide did not inhibit neuronal uptake of noradrenaline. The potentiating action of 5-HT on norndrenline responses, but not that of angiotensin II, was calcium-dependent. This action of angiotensin II appeared to be a membrane effect, and the involvement of membrane pumps was examined. The actions of angiotensin II on the rabbit isolated aorta, both direct contractor and indirect potentiation, appeared to be related to the ratio of intracellular to extracellular sodium ions. An attempt was made to provide c comprehensive theory for the mechanism of the potentiating and contractor actions of 8ngiotensin II in terms of ion fluxes and cellular metabolism in the vascular smooth muscle cell. Finally, the action of the diuretic drug frusemide was examined on the blood pressure responses of the pithed r0t to vascular spasmogens. Neither pre-treatment nor acute intra-peritoneal injection had a significant effect on the responses of the preparation. However, acute intravenous injection of frusemide had a specific anti-angiotensin II potion in just over half of the animals studied. This action is discussed in terms of the possible ionic fluxes induced by frusemide.