Possible direct effect of gonadotropin releasing hormone on human endometrium and decidua

Decidualization of endometrial tissues, which is essential for implantation and the continuation of pregnancy, is induced by pituitary hormones that are regulated by gonadotropin releasing hormone (GnRH). Our objective was to determine the role of a direct action of GnRH on endometrial tissues by comparing the characteristics of receptors for GnRH in human endometrial and decidual tissues. Competitive binding studies were performed with the protease-resistant GnRH analogues, buserelin and [125I] buserelin. The effects of buserelin on phosphoinositol turnover were determined by the measurement of inositol 1,4,5-triphosphate(IP3). The values for the dissociation constant (Kd) and number of binding sites (Bmax) per unit protein versus buserelin for endometrial tissues did not differ from the values for decidual tissues. However, the Bmax per unit DNA was significantly higher in endometrial tissues. Also, buserelin induced a significant increase in IP3 in decidual tissue. These results indicate that GnRH may be a potential modulator of the function in human endometrium and decidua. The signal transduction mechanism for GnRH action appeared to involve the accelerated turnover of phosphoinositol.