MOLECULAR AND FUNCTIONAL-CHARACTERIZATION OF V-1B VASOPRESSIN RECEPTOR IN RAT ADRENAL-MEDULLA

In rat adrenal medulla, PCR experiments reveal the expression of messe nger RNA encoding the gene for the V-1b vasopressin receptor. Compleme ntary 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 cu ltures showed that vasopressin dose dependently mobilized intracellula r calcium, suggesting that functional vasopressin receptors are expres sed in these tissues. The use of d[D-3-Pal]vasopressin, a specific V-1 b vasopressin agonist, and SR 49059, a specific V-1a vasopressin antag onist, revealed that V-1b recvasopressin antagonist, revealed that V-1 b receptors are exclusively expressed in adrenal medulla. Using an ind irect immunological approach (plasma membrane localization of dopamine -beta-hydroxylase), we demonstrated that stimulation of rat adrenal me dulla V-1b receptor leads to catecholamine secretion. More interesting ly, PCR experiments performed on rat adrenal medulla RNA revealed that the arginine vasopressin-encoding gene is also expressed in this tiss ue. In addition, perifusion experiments indicated that [Arg(8)]vasopre ssin is released by the adrenal medulla. Together, these data suggest that vasopressin may regulate the adrenal functions by paracrine/autoc rine mechanisms involving distinct vasopressin receptor subtypes: V-1a in the adrenal cortex and V-1b in the adrenal medulla.