Possible modes of action of dobutamine in dog femoral and pulmonary arteries.

Possible mechanisms involved in the action of dobutamine on blood vessels in isolated strips of dog artery were investigated and compared with noradrenaline, dopamine, and isoprenaline. In femoral strips, noradrenaline, dopamine, and dobutamine induced a dose-dependent contraction which was blocked by phenoxybenzamine. In strips previously contracted by KCl, after pretreatment with phenoxybenzamine, dobutamine induced a further contraction while isoprenaline produced a dose-dependent relaxation. However, dobutamine and isoprenaline elicited a dose-dependent relaxation in strips contracted by noradrenaline without phenoxybenzamine. This isoprenaline-induced relaxation was completely blocked by propranolol but the dobutamine-induced relaxation was in part attenuated by propranolol. In pulmonary strips, noradrenaline and dopamine elicited a dose-dependent contraction which was blocked by phenoxybenzamine, whereas dobutamine did not act on the strips. beta-Blockade by propranolol tended to potentiate the dobutamine-induced contraction of femoral strips, but did not affect the responses of pulmonary artery to dobutamine. In pulmonary arteries, the contractile responses to noradrenaline were antagonised by dobutamine. The results obtained here indicate that dobutamine exerts vascular actions by several different modes, such as an alpha-adrenergic agonistic and antagonistic action, an extremely weak beta 2 agonistic action, and a non-adrenergic contractile action.