ESTROGEN REGULATION OF GONADOTROPIN-RELEASING-HORMONE RECEPTOR MESSENGER-RNA IN FEMALE RAT PITUITARY TISSUE

Gonadotropin releasing hormone (GnRH) is crucial in regulating the rep roductive system of female vertebrates. In the present study we have a nalyzed the estrogen regulation of the GnRH receptor mRNA at the cellu lar level in Sprague-Dawley female rats. Northern blot analysis detect ed 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 increas ed by estrogen. By in situ hybridization we observed a 3.5-fold increa se 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 mR NA levels by estrogen were also found in Wistar-Imamichi female rat pi tuitary tissue. In situ hybridization analysis identified clusters of anterior pituitary cells that expressed the GnRH receptor mRNA. The es tradiol effect depends on increased mRNA levels in these clusters. Mor eover, a significant increase in the number of pituitary cells that ex pressed GnRH receptor was observed after 48 h of estrogen treatment. T hese findings suggest that the mechanisms for estrogen regulation of G nRH receptor include changing levels of GnRH receptor mRNA in the rat pituitary.