Absence of a relationship between sympathetic neuronal activity and turnover of serum dopamine-?-hydroxylase

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Abstract
The effects of pharmacological alteration of adrenergic transmission on the rate of entrance of dopamine-β-hydroxylase (DBH) into the circulation were assessed in rats by an immunological method in which the kinetics of recovery of serum DBH activity were measured after depletion of the enzyme by treatment with anti-rat DBH antiserum. Neither α-receptor blockade with phenoxybenzamine nor ganglionic blockade with clorisondamine altered the rate by which DBH enters the bloodstream although both treatments markedly altered serum catecholamine levels. Prolonged treatment of newborn rats with guanethidine produced a severe peripheral sympathectomy but only a moderate decrease (30%) in serum DBH levels. In the sympathectomized rats, the rate of entrance of DBH into the circulation was significantly reduced whereas the half-life and rate of degradation of the enzyme was unchanged. These results indicate that the major portion of serum DBH does not enter the circulation by means of exocytotic release of the soluble enzyme.