6533b7dcfe1ef96bd1271701

RESEARCH PRODUCT

The effect of dopamine on the overflow of endogenous noradrenaline from the perfused rabbit heart evoked by sympathetic nerve stimulation.

subject

description

1. The effects of dopamine and two dopamine receptor antagonists (pimozide, flupenthixol) on the release of endogenous noradrenaline evoked by electrical stimulation of the postganglionic sympathetic nerves and their influence on cardiac performance were measured in isolated perfused rabbit hearts. 2. Dopamine 0.2μM decreased noradrenaline overflow and ventricular tension development in response to nerve stimulation. 3. Dopamine 2μM increased spontaneous noradrenaline output and tension development. The noradrenaline overflow in response to nerve stimulation was greatly enhanced. This action was only partly reversed by wash out of exogenous dopamine, indicating de novo synthesis and facilitated release of noradrenaline. 4. Pimozide (approximately 1μM) and flupenthixol 5μM had no effect on noradrenaline overflow and cardiac peroormance. 5. In the presence of cocaine 18.3μM dopamine 2μM decreased the overflow of noradrenaline. This effect was fully antagonized by flupenthixol which on its own neither influenced transmitter overflow nor antagonized the presynaptic inhibitory effect of oxymetazoline 0.38μM. 6. It is concluded that in the rabbit heart dopamine has an inhibitory effect on the release of endogenous noradrenaline which appears to be, mediated by presynaptic dopamine receptors and which differs from the prejunctional α-adrenoceptor mediated negative feedback mechanism.