Potentiation of Human Vascular Smooth Muscle Contraction by Angiotensin

One of the possible sites of interaction between angiotensin and the sympathetic nervous system in man is at the level of vascular smooth muscle contraction. This study has used human vascular preparations to explore the potentiating effect of subcontractile concentrations of angiotensin on the contractile effects of other agonists, particularly norepinephrine. Angiotensin potentiated the effects of norepinephrine such that in the presence of angiotensin, approximately half the concentration of norepinephrine was required to produce the same contractile effect as in its absence. This potentiating effect occurred at concentrations of angiotensin approximately one-tenth of those that of themselves produced a contractile effect. Angiotensin, but not norepinephrine, also potentiated the contractile effects of 5-hydroxytryptamine, potassium chloride, and barium chloride. Barium chloride potentiated the contractile effects of norepinephrine to an extent similar to angiotensin, and 5-hydroxytryptamine and potassium chloride potentiated the effect of norepinephrine to a significantly lesser degree. Angiotensin potentiation occurred in the absence of external calcium ions. It is concluded firstly that angiotensin has a nonspecific potentiating effect on human vascular smooth muscle contraction, and secondly that it occurs at concentrations similar to those occurring in vivo and thus may be of clinical importance.