Molecular and functional characterization of V-1b vasopressin receptor in rat adrenal medulla

In rat adrenal medulla, PCR experiments reveal the expression of messenger RNA encoding the gene for the V-1b vasopressin receptor. Complementary DNA amplified sequences corresponded to the cloned rat pituitary V-1b 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 V-1b vasopressin agonist, and SR 49059, a specific V-1a vasopressin antagonist, revealed that V-1b recvasopressin antagonist, revealed that V-1b 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 V-1b 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 [Arg(8)]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: V-1a in the adrenal cortex and V-1b in the adrenal medulla.