Characterization of high affinity binding sites for vasopressin in bovine adrenal medulla.

A crude membrane fraction prepared from bovine adrenal medulla bound tritium labeled arginine-vasopressin (3H-AVP) in a time and temperature dependent manner. Physiological concentrations of Mg2+ (1-3 mmol/l) were required for the binding reaction, while Ca2+ (5-80 mmol/l) had no effect. The reaction was saturable and reversible. Scatchard plots of the data suggested the presence of a single class of high affinity (Kd=0.41 nmol/l) and low capacity (Bmax=26 fmol/mg protein) binding sites. The specificity of the binding reaction was examined using various structural analogs of AVP which displaced 3H-AVP. Arginine-vasotocin proved to be equipotent with AVP, while oxytocin and 1-deamino,8-D-arginine-vasopressin were about 500-fold less effective. Two relatively selective V1-receptor antagonists, dPenTyrMeAVP and d(CH2)5-TyrMeAVP were 2- and 20-fold less potent than AVP, respectively These data strongly suggest that the bovine adrenal medulla contains V1-type receptors for vasopressin, which could be involved in the regulation of the function of chromaffin cells.