Study of oxytocin receptor in human myometrium using highly specific 3H-labeled oxytocin.

Abstract

A highly specific 3H-labeled oxytocin (3H-OT) was synthesized utilizing the method of catalytic substitution of halogen for hydrogen. The specific activity of 3H-OT was 19 Ci/mM and the biologic activity was 350 U[units]/mg, which was sufficient for the OT radioreceptor assay. The maximum percent uptake of 3H-OT in the human myometrium was observed in 20,000 .times. g pellets under the optimal conditions of pH 7.4, at 20.degree. C and the incubation time of 90 min and it was augmented in the presence of Mn2+. It was also observed from the Scatchard plot, that the binding site of OT in the human myometrial specimens was a single type within the range of OT concentration of 0.4-1.6 nM. The Kd and the number of binding sites (NBS) showed a relative increase as gestation advanced. The apparent Kd of term pregnancies was 1.25 .times. 10-9 M regardless of the presence or absence of labor pains, while the NBS of term pregnancies with and without labor pain was 1.2 .times. 10-12 and 4.7 .times. 10-12 mol/mg protein, respectively.