Catecholamine depletion as a factor in the induction of adrenal tyrosine hydroxylase

Abstract

1. 1. The activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamines, was measured in homogenates of rat adrenal gland following various drugs to determine whether depletion of catecholamines may also be a factor in induction of TH. 2. 2. In contrast to reserpine, treatment of rats with guanethidine for 1 day or 4 days failed to elevate adrenal TH activity, suggesting that hypotension (and the subsequent increase in nerve activity) is not sufficient stimulus for induction of adrenal TH. 3. 3. Reserpine depletes the adrenal catecholamine, whereas guanethidine does not do so. It seems that depletion of catecholamine by reserpine may also be a factor which can lead to an increase in adrenal activity. 4. 4. Support for the suggestion is derived from the observation that interference with reserpine-induced depletion of catecholamine by pargyline, reduced the increase in adrenal TH activity by reserpine. 5. 5. Phentolamine which does not deplete catecholamine failed to cause induction of TH. 6. 6. It is concluded that depletion of catecholamines may also be a factor regulating adrenergic TH activity.