Molecular and functional characterization of V1b vasopressin receptor in rat adrenal medulla

In rat adrenal medulla, PCR experiments reveal the expression of messenger RNA encoding the gene for the V1b vasopressin receptor. Complementary DNA amplified sequences corresponded to the cloned rat pituitary V1b vasopressin receptor. Video microscopy experiments performed on fura-2-loaded adrenal medullary or adrenal glomerulosa cell primary cultures showed that vasopressin dose dependently mobilized intracellular calcium, suggesting that functional vasopressin receptors are expressed in these tissues. The use of d[D-3-Pal]vasopressin, a specific V1b vasopressin agonist, and SR 49059, a specific V1b vasopressin antagonist, revealed that V1b receptors are exclusively expressed in adrenal medulla. Using an indirect immunological approach (plasma membrane localization of dopamine-beta-hydroxylase), we demonstrated that stimulation of rat adrenal medulla V1b receptor leads to catecholamine secretion. More interestingly, PCR experiments performed on rat adrenal medulla RNA revealed that the arginine vasopressin-encoding gene is also expressed in this tissue. In addition, perifusion experiments indicated that [Arg8] vasopressin is released by the adrenal medulla. Together, these data suggest that vasopressin may regulate the adrenal functions by paracrine/autocrine mechanisms involving distinct vasopressin receptor subtypes: V1a in the adrenal cortex and V1b in the adrenal medulla.