ONTOGENY OF GENE-EXPRESSION IN THE GONADOTROPH OF THE DEVELOPING FEMALE RAT

During the infantile period of the female rat (8-21 postnatal days [PN D] of age), there is a dramatic increase in plasma FSH, which is thoug ht to be important in initiating ovarian activity and, perhaps, the on set of puberty. To begin to understand the regulation of this FSH surg e, we determined the ontogenetic development of LH beta, FSH beta, and GnRH receptor (GnRH-R) mRNA levels in the pituitary gland throughout the infantile period of the female rat. Steady-state mRNA levels were determined by an external standard quantitative reverse transcriptase polymerase chain reaction assay. FSH beta and GnRH-R mRNA levels incre ased to peak on PND 12 (p < 0.03). LH beta mRNA levels remained relati vely constant until rising on PND 18. A GnRH antagonist (10-100 mu g/a nimal) was administered daily from PND 8-11 or PND 11-13, and animals were killed on PND 12 or PND 14, respectively. FSH beta, LH beta, and GnRH-R mRNAs were not affected by GnRH antagonist treatment. Plasma FS H was selectively reduced in the first group, whereas both plasma LH a nd FSH were suppressed in the second group. These data indicate that g ene expression of LH beta, FSH beta, and GnRH-R are differentially reg ulated in the infantile female rat pituitary. GnRH is involved in regu lating the secretion of FSH and LH during the infantile period but not in regulating FSH beta, LH beta, or GnRH-R mRNA gene expression.