Rat gonadotropin-releasing hormone (GnRH) receptor: tissue expression and hormonal regulation of its mRNA.

The binding of gonadotropin-releasing hormone (GnRH) to its receptor in the anterior pituitary gland is the key molecular interaction regulating the reproductive process of mammals. Here, we report the isolation of a cDNA representing this receptor from rat anterior pituitary and the regulation of expression of its mRNA. The rat GnRH receptor cDNA was composed of 2909 nucleotides and encoded a protein containing 327 amino acids having a seven transmembrane topology. Northern blot analysis on RNA from rat pituitary, ovary and testis showed four different transcripts (5.0, 4.5, 2.5 and 1.3 kb) of which the 5.0 kb form was most abundant. The levels of expression of the transcripts were found to be highest in the pituitary followed by the ovary and the testis (about 40% and 5% compared to pituitary, respectively). Using the more sensitive reverse transcriptase/PCR technique, we also detected GnRH receptor mRNA in the adrenal and the hypothalamus. Measurement of pituitary GnRH receptor mRNA levels (the 5.0 kb form) during the estrous cycle showed the lowest levels at estrus (1.0-fold), a 2.2 +/- 0.57 (mean +/- SEM) -fold increase at diestrus I, a 3.5 +/- 0.41-fold increase at diestrus II, a 2.6 +/- 0.34-fold increase on the morning of proestrus, and a 1.9 +/- 0.25-fold on the afternoon of proestrus. Removal of the ovaries led to a 2.7 +/- 0.29-fold increase in GnRH receptor mRNA levels in the pituitary gland; treatment of ovariectomized rats with estrogen resulted in a significant decrease in GnRH receptor mRNA levels. Our studies demonstrate ovarian regulation of GnRH receptor mRNA expression in the anterior pituitary gland.