Estrogen regulation of gonadotropin-releasing hormone receptor messenger RNA in female rat pituitary tissue.

Abstract

Gonadotropin releasing hormone (GnRH) is crucial in regulating the reproductive system of female vertebrates. In the present study we have analyzed the estrogen regulation of the GnRH receptor mRNA at the cellular level in Sprague-Dawley female rats. Northern blot analysis detected 3 species (5.0, 4.5 and 1.4 kb) of GnRH receptor mRNA in pituitary tissues. The GnRH receptor mRNA levels of these 3 species were increased by estrogen. By in situ hybridization we observed a 3.5-fold increase in GnRH receptor mRNA levels after 48 h of estrogen treatment when compared to ovariectomized (OVX) rats, 12 h of estrogen treatment did not change the GnRH mRNA levels. Similar increases in GnRH receptor mRNA levels by estrogen were also found in Wistar-Imamichi female rat pituitary tissue. In situ hybridization analysis identified clusters of anterior pituitary cells that expressed the GnRH receptor mRNA. The estradiol effect depends on increased mRNA levels in these clusters. Moreover, a significant increase in the number of pituitary cells that expressed GnRH receptor was observed after 48 h of estrogen treatment. These findings suggest that the mechanisms for estrogen regulation of GnRH receptor include changing levels of GnRH receptor mRNA in the rat pituitary.