Origin of dopamine in the rat adrenal cortex.
The hypothesis that dopamine (DA) is involved in the control of aldosterone secretion is given some support by the finding of DA in the adrenal cortex of several species, but the source of this DA is not known. This study showed that the administration of L-dopa to intact rats or medullectomized rats caused a significant DA increase in the adrenal cortex. The DA increase in the cortex was more pronounced than in the medulla, coincident with higher L-dopa uptake by the cortical tissue. Tyrosine administration raised DA levels only in the medulla. Sympathectomy of the rat by 6-hydroxydopamine treatment did not affect DA basal levels in the cortex or the DA increase in this tissue after L-dopa injection. 3,4-Dihydroxyphenylacetic acid (DOPAC) is detectable in the adrenal cortex but not in the adrenal medulla, and DOPAC levels increased significantly after L-dopa, which indicates monoamine oxidase (MAO) activity within the adrenal cortex. Because 6-hydroxydopamine pretreatment did not alter DOPAC levels, cortical MAO may be located outside catecholaminergic neurons. The results established circulating L-dopa as a precursor for DA in the adrenal cortex of the rat. They also showed that tyrosine hydroxylase activity is absent from the adrenal cortex of this species.