EFFECT OF ANGIOTENSIN ON VASCULAR SMOOTH MUSCLES

The response of vascular smooth muscle to angiotensin has been studied on helical strips of canine coronary, renal, and carotid arteries and on strips of the thoracic aorta from guinea pigs and rats. 1. Following repeated application of angiotensin tachyphylaxis had developed in all vascular strips that were examined. 2. Reversal of tachyphylaxis could not be demonstrated after incubation of the vascular strips and replenishment of the adrenergic vesicles with norepinephrine. When the vascular strips had been incubated with norepinephrine a mean contraction of 26.7% of the initial reaction occured. 3. Following incubation of the vascular strips with angiotensinase containing kidney extract a certain degree of reversal of tachyphylaxis was apparent, which, however, could not be reproduced in all experiments. In experiments on aortic strips of guinea pigs and rats it has been shown that the effect of angiotensin during the tachyphylactic state is dependent on the interval between consecutive applications of angiotensin. 4. The results of our experiments do not support the hypothesis of indirect angiotensin action by liberation of norepinephrine from the adrenergic vesicles because: a) Following norepinephrine incubation tachyphylaxis could not be abolished or reduced. b) The action of angiotensin could not be modified after blockade of the adrenergic α-receptors. c) Angiotensin exclusively caused contraction on strips of coronary arteries. © 1969 Springer-Verlag.