Expression and localization of human dopamine D2 and D4 receptor mRNA in the adrenal gland, aldosterone-producing adenoma, and pheochromocytoma

Aldosterone secretion is evidently regulated by a dopaminergic inhibitory m echanism. Pharmacological characterization and autoradiographic studies rev ealed D2-like receptors in the adrenal cortex, especially in the zona glome rulosa. However, the subtype of the dopamine receptors involving this regul ation has not been elucidated. To investigate which sub-type of receptors e xpresses in the adrenal cortex, we examined the messages of D2-like recepto rs, D2, D3, and D4, by RT-PCR and in situ hybridization of adrenal glands a nd adrenal neoplasm. Both D2 and D4 receptors were expressed in normal adre nal glands, pheochromocytoma, and aldosterone-producing adenoma. However, t he D2 receptors were not universally expressed, in contrast with the D4 rec eptors that were detected in all cases of aldosterone-producing adenoma and adrenal remnant. No D3 receptor message was detected by RT-PCR in any adre nal sample. Both D2 and D4 receptors were expressed in significant amounts in the adrenal medulla and pheochromocytoma. In the adrenal cortex, the exp ression of the D2 receptors was in the zona glomerulosa and zona reticulari s, with no different signal intensities between the two zones. D4 receptors were mainly localized in the zona glomerulosa and, to a lesser extent, in the zona reticularis. Both receptors were expressed at low levels in the zo na fasciculata. In aldosterone-producing adenoma, the expression of D2 and D4 was especially found in nonzona fasciculata-like cells. To elucidate whi ch dopamine receptor regulates aldosterone secretion, the effects of specif ic D2 and D4 antagonists, raclopride and clozapine, respectively, were exam ined in cultured NCI-H295 cells. Dopamine further increased angiotensin II- induced aldosterone secretion by 20%. In the presence of 1 muM dopamine and angiotensin II, 10(-5)-10(-7) M clozapine decreased aldosterone levels by 40-55%. The decrease in aldosterone secretion by clozapine was completely r eversed when raclopride was added simultaneously. These data suggest that d opamine exerts dual effects on aldosterone secretion in NCI-H295 cells. Act ivation of D4 receptors can increase aldosterone secretion, whereas an inhi bitory effect is mediated via D2 receptors. In summary, we demonstrated the existence of both D2 and D4 receptors in the human adrenal gland and adren al neoplasm. Both receptors play significant roles in the modulation of ald osterone secretion, but in opposite directions.