[Steroid levels and myometrial sensitivity to oxytocin]

To examine the relation between changes in steroid concentrations in serum and myometrium and the uterine sensitivity to oxytocin, sixteen steroids including free and conjugated progesterone, 16 alpha OH-progesterone, 20 alpha OH-progesterone, cortisol, 16 alpha OH-pregnenolone, DHA, 16 alpha OH-DHA, estrone, estradiol, estriol in serum and myometrium were measured simultaneously by RIA. 83 pregnant women near term were selected for this study and steroid levels were measured in 66 cases. There was a significant correlation between days to the onset of labor and myometrial sensitivity to oxytocin estimated by the Smyth test. The levels of 16 alpha OH-progesterone, 20 alpha OH-progesterone, cortisol, 16 alpha OH-pregnenolone, conjugated 16 alpha OH pregnenolone, estrone, estradiol, conjugated estrone, conjugated estradiol, conjugated estriol, conjugated DHA and conjugated 16 alpha OH-DHA increased as the uterine sensitivity to oxytocin increased, while the levels of progesterone decreased significantly. The ratios of 20 alpha OH-progesterone to progesterone and estradiol to progesterone also rose significantly, while the ratio of free to conjugated DHA fell significantly. Serial determination of steroid levels and ratios and sensitivity to oxytocin revealed a similar pattern to that mentioned above. There was a significant correlation between serum and myometrial concentrations of progesterone, 16 alpha OH-pregnenolone, DHA, conjugated DHA, estrone and estradiol. From these results it was concluded that the environment of steroid hormones may be closely related to myometrial sensitivity to oxytocin and the onset of labor.