Ontogeny of gene expression in the gonadotroph of the developing female rat.

During the infantile period of the female rat (8-21 postnatal days [PND] of age), there is a dramatic increase in plasma FSH, which is thought to be important in initiating ovarian activity and, perhaps, the onset of puberty. To begin to understand the regulation of this FSH surge, we determined the ontogenetic development of LHbeta, FSHbeta, 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. FSHbeta and GnRH-R mRNA levels increased to peak on PND 12 (p < 0.03). LHbeta mRNA levels remained relatively constant until rising on PND 18. A GnRH antagonist (10-100 microg/animal) was administered daily from PND 8-11 or PND 11-13, and animals were killed on PND 12 or PND 14, respectively. FSHbeta, LHbeta, and GnRH-R mRNAs were not affected by GnRH antagonist treatment. Plasma FSH was selectively reduced in the first group, whereas both plasma LH and FSH were suppressed in the second group. These data indicate that gene expression of LHbeta, FSHbeta, and GnRH-R are differentially regulated in the infantile female rat pituitary. GnRH is involved in regulating the secretion of FSH and LH during the infantile period but not in regulating FSHbeta, LHbeta, or GnRH-R mRNA gene expression.