[The interaction of oxytocin-prostaglandin receptors in human myometrium and amnio-decidua throughout pregnancy and in labor].

: This study was designed to investigate the interaction of oxytocin and prostaglandin F2 alpha at the receptor level (OXT-R and PGF2 alpha-R) between the myometrium and amnio-decidua throughout pregnancy and at parturition in an effort to clarify which of the two is the first and/or triggering factor involved in the instigation of myometrial contractions. In rat myometria, it was recognized that PGF2 alpha-R increased from day 20 of pregnancy and preceded that of OXT-R from day 22 and thereafter both reached peak levels at delivery. In human myometria, on the other hand, OXT-R showed an increase as gestation advanced and when labor was initiated, a significant decrease was found regardless of the route of labor, while the PGF2 alpha-R the binding capacity of which was only 1/20-1/30 of OXT-R, did not change throughout pregnancy or in labor. The binding affinity of OXT-R in amnio-decidua increased as gestation advanced, while its binding capacity remained unchanged and after the onset of labor that of the amnion decreased significantly even though it was only 1/6-1/7 that of the myometrium. The binding affinity of myometrial OXT-R was elevated following the addition of PGF2 alpha before the onset of labor, but the converse could not be shown. These findings suggest that the instigation and maintenance of human labor may be firstly and/or initially dependent on the increase of the binding activity between OXT and OXT-R in the myometrium, and the PGF2 alpha may facilitate such activity by the allosteric effect on OXT-R directly or on the plasma membrane to increase its binding affinity.