Regulation of Dopamine @-Hydroxylase in Rat Adrenal Glands

Rat adrenal gland levels of dopamine &hydroxylase are subject to dual control. Activation of the splanchnic nerves to the adrenal medulla by reserpine induces the synthesis of dopamine /3-hydroxylase without altering the rate of enzyme degradation. In contrast, hypophysectomy causes a decline in steady state dopamine fi-hydroxylase levels by first accelerating the rate of degradation, then by slowing the rate of enzyme synthesis as well. Adrenocorticotropic hormone administration partially reversed the effect of hypophysectomy on dopamine B-hydroxylase degradation. These findings suggest that the trans-synaptic factors controlling dopamine P-hydroxylase induction act by a different mechanism (enzyme synthesis) than the hormonal controls regulating steady state levels (enzyme degradation). Thus, active inhibition of enzyme degradation may be an important control in maintenance of steady state enzyme levels.