The uptake of dopamine-14C and its conversion to noradrenaline-14C in rats.

The scheme of biosynthesis of noradrenaline from dopa in the mammalian tissues was presented by Blaschko (1). The conversion of dopamine to noradrenaline, mediated by dopamine-Q-hydroxylase (2), was shown to occur in the intracellular granules of the adrenal medulla (3) and heart (4, 5). The administration of tyrosine-14C (6) or dopa 14C (7 , 8) to rats results in formation of noradrenaline-14C in sympathetically innervated tissues. Though the biosynthesis of noradrenaline from the exogenously administered dopamine is established, little information is available regarding the amount of dopamine 14C remaining in tissues and its conversion to noradrenaline -14C against time after the injection of labelled dopamine. The increased formation of noradrenaline following stimulation of the sympathetic nerve has been demonstrated in the submaxillary gland (9) and vas deferens (10). The facts suggest a possible regulation of catecholamine synthesis by sympathetic nerve activity. The present experiments were undertaken to examine further the role of sympathetic nerve activity in the turnover rate of dopamine. The rate of disappearance of dopamine 14C in salivary glands after the injection , and the formation of noradrenaline-14C were measured on the decetralized rat submaxillary gland. Additional studies were made on other sympathetically innervated tissues.