The influence of angiotensin on the uptake of noradrenaline by the isolated heart of the rabbit

Abstract

The influence of angiotensin on the removal of noradrenaline (10 ng/ml) from the perfusion medium and on the net-uptake of noradrenaline (5 and 20 μg/ml) was examined in the rabbit isolated heart. Concentrations of angiotensin, known to augment the output of noradrenaline from rabbit heart during sympathetic nerve stimulation, did not inhibit the removal of infused noradrenaline from the perfusion fluid. Only very high concentrations of angiotensin (13 μg/ml) significantly diminished the loss of noradrenaline. The positive inotropic effect of noradrenaline was not potentiated by angiotensin. On the other hand, cocaine, in doses which enhance the output of noradrenaline during sympathetic stimulation greatly reduced the loss of noradrenaline from the perfusion fluid. Neither angiotensin (130 ng/ml) nor metanephrine (5 and 20 μg/ml) significantly influenced the net-uptake of noradrenaline from high concentrations. The observations made support the assumption that an increase of transmitter liberation rather than inhibition of transmitter inactivation is responsible for the increase caused by angiotensin in the output of noradrenaline during stimulation of sympathetic nerves.