BABOON CORPUS-LUTEUM - PRESENCE OF OXYTOCIN RECEPTORS

To determine whether the effect of oxytocin (OT) on progesterone produ ction in primate luteal tissue may be receptor-mediated, we used bioch emical procedures to examine the CL of the baboon (Papio anubis) for t he presence of OT receptors (OT-R). CL (n = 5) were obtained by luteec tomy from die early (LH + 1-5 days), mid- (LH + 6-10 days), and late ( LH + 10-15 days) luteal phases. Biopsies from the uterine fundus were also obtained at the same time. Total receptors were measured by incub ating the membrane fractions (120 000 X g fraction) with increasing co ncentrations of [H-3]oxytocin (0.08-1.6 nM) for 30 min at 22-degrees-C with a protein concentration of 200 mug per tube. Nonspecific binding was evaluated by the addition of excess nonradioactive OT, The recept or-bound tritiated ligand was separated from the nonreceptor-bound lig and through use of polyethylene glycol. For the midluteal phase CL, th e affinity K(d) was 1.70 +/- 0.03 nmol/L and the mean receptor number (RT) was 122.6 t 8.3 fmol/mg protein. In comparison, myometrial tissue examined at the same phase of the cycle had a K(d) of 1.3 +/- 0.1 nmo l/L and an RT of 205.0 +/- 49.7 fmol/mg protein. Receptors were not de tectable in the late luteal phase CL and were significantly lower in t he early luteal phase CL (50.7 +/- 6.9 fmol/mg protein), with no diffe rence in the K(d) value. Competitive studies with structurally related and nonrelated peptides indicated the presence of specific receptors for OT in baboon CL. The presence of receptors in the tissue suggests that the effect of OT on CL progesterone production is probably recept or-mediated.