Study of Oxytocin Receptor in Human Myometrium Using Highly Specific 3H-Labeled Oxytocin

Abstract

A highly specific tritium labeled oxytocin (3H-OT) was synthesized utilizing the method of catalytic substitution of halogen for hydrogen. The specific activity of 3H-OT was 19Ci/mM and the biologic activity was 350U/mg, which was sufficient for the OT radioreceptor assay. The maximum % uptake of 3H-OT in the human myometrium was observed in 20,000Xg pellets under the optimal conditions of pH 7.4, at 20°C and the incubation time of 90min and it was augmented in the presence of Mn++. 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 0.4nM to 1.6 nM. The dissociation constants (Kd) and the number of binding sites (NBS) showed a relative increase as gestation advance. The apparent Kd of term pregnancies was 1.25x10-9 M regardless of the presence or absence of labor pains, while the NBS of term pregnancies with and without labor pain was 1.2x10-12 and 4.7 x 10-12 moles/mg protein, respectively. © 1979, The Japan Endocrine Society. All rights reserved.