alpha 2-Adrenergic receptors inhibit catecholamine secretion from bovine adrenal medulla

Catecholamine secretion evoked by carbamylcholine from isolated bovine adrenal medullary cells was inhibited by alpha 2-agonist, clonidine, in a dose-dependent manner with IC50 value of 2.8 X 10(-5) M. [3H]Clonidine bound to adrenal medullary membranes with high affinity and saturable characteristics. These results suggest that alpha 2-adrenergic receptors which exist on adrenal medullary cells have inhibitory effect on the secretion of catecholamine from the cells.