Role of adrenal hormones in the synthesis of noradrenaline in cardiac sympathetic neurones.

1. Adrenalectomy or adrenal demedullation affected neither the levels of endogenous catecholamines in the rat heart nor the accumulation of (3)H-noradrenaline 1 hr after its intravenous administration.2. Twenty-four hours after intravenous administration of labelled amine, however, its retention was markedly reduced in the heart of adrenalectomized or demedullated rats. Ganglionic blockade prevented this reduction.3. Rate calculations from the decline of catecholamine levels after blockade of synthesis with alpha-methyl-tyrosine showed that cardiac synthesis of noradrenaline increased about four-fold after demedullation and about three-fold after adrenalectomy. This increase in synthesis may compensate for the loss of circulating catecholamines.4. There was no change in catechol-o-methyl-transferase activity, but monoamine oxidase activity was increased in the homogenates of the heart of adrenalectomized and demedullated rats. The increase in the cardiac monoamine oxidase activity was markedly greater in the adrenalectomized rats than in the demedullated rats.5. It is suggested that adrenal cortex insufficiency may modulate the rate of synthesis of noradrenaline and monoamine oxidase activity in cardiac sympathetic neurones.