Selective augmentation of cellular hCG alpha mRNA levels and immunoreactive hCG alpha secretion by 17 beta-estradiol in the normal placenta

Abstract

In order to elucidate a possible self-regulation for hCG synthesis in placenta, effects of estradiol on hCG production and secretion were evaluated by culturing early placental tissue in the presence or absence of estradiol. The cellular level of mRNAs encoding hCG (alpha, beta) and hPL were estimated by mean grain count per syncytial nucleus on the placental sections hybridized in situ with labeled cDNA probes corresponding to these mRNAs. Immunoreactive hCG, hCG alpha and hPL in the media and explanted tissues were measured by the homologous RIAs. Addition of estradiol at concentration of 1 approximately 10 ng/ml into the medium caused an increase in the cellular levels of hCG alpha mRNA after 24-hour cultured, and exhibited significant increases in immunoreactive hCG alpha levels in the media and explanted tissues after 72-hour culture. The addition of estradiol neither affected the cellular levels of mRNA encoding hCG beta and hPL nor immunoreactive hCG and hPL levels in the media and tissues. The appropriated concentration of estradiol (1 approximately 10 ng/ml) used in above experiments was found to be similar to the tissue concentration in normal placenta. These findings suggest that the physiological concentration of estradiol selectively stimulates hCG alpha synthesis and secretion by normal placenta. Thus, estradiol in placenta may be a factor responsible for the increase of hCG alpha in maternal serum and placental tissue with the progress of gestation.