ACTH increases noradrenaline release in the rabbit heart

The effects of ACTH on the release of noradrenaline and the increase of heart rate produced by sympathetic nerve stimulation (1 Hz) were studied in isolated perfused rabbit hearts. ACTH-(1-24) 0.1-100 nmol/l increased the stimulation-evoked overflow of noradrenaline concentration-dependently, reversibly and up to two-fold. The basal outflow of noradrenaline, the basal heart rate and the stimulation-evoked increase in heart rate were not changed. Human ACTH-(1-39) also increased the evoked overflow of noradrenaline. The effect of ACTH-(1-24) 0.3 nmol/l persisted after blockade of beta-adrenoceptors with propranolol and blockade of neuronal catecholamine uptake by cocaine. ACTH-(1-24) 3 nmol/l did not change the removal of noradrenaline from the perfusion fluid, when hearts were perfused with medium containing 59 nmol/l noradrenaline. The results show that ACTH increases the action potential-evoked release of noradrenaline from cardiac postganglionic sympathetic neurones, probably by activating specific presynaptic ACTH receptors. The high potency of ACTH suggests that these presynaptic receptors may be activated in vivo by circulating ACTH under certain pathophysiological conditions.