GONADAL-STEROIDS REGULATE RAT ANTERIOR-PITUITARY LEVELS OF TSH-RELEASING HORMONE-LIKE AND PYROGLUTAMYL-GLUTAMYL-PROLINE AMIDE-LIKE IMMUNOREACTIVITY

The novel peptide, pyroglutamylglutamylprolineamide (pGlu-Glu-ProNH(2), EEP), which has structural and immunological similarities to TRH (pGlu-His-ProNH(2)) has recently been shown to contribute to total TRH-like immunoreactivity (t-TRH-LI) detected in the rabbit prostate and rat and porcine anterior pituitary. This study was undertaken to determine the effects of gonadal steroids on t-TRH-LI and its components in the rat hypothalamus and pituitary. EEP-like immunoreactivity (EEP-LI) was separated from TRH-LI by ion exchange chromatography and detected by TRH RIA. Although male and female posterior pituitary and hypothalamic t-TRH-LI levels were similar, the mean t-TRH-LI in female anterior pituitaries was significantly lower than that in males, 10.3 +/- 2.9 pmol/g vs. 24.4 +/- 2.5 pmol/g (P < 0.01). Anion exchange analysis of control anterior pituitary samples distinguished two peaks of t-TRH-LI, corresponding to [I-125]-TRH marker and [H-3]-EEP markers. In control female anterior pituitaries EEP-LI accounted for 26.0 +/- 2.4% of t-TRH-LI, whereas in males it accounted for 43.3 +/- 5.3% of the total. Hypothalamic and posterior Pituitary samples only contained t-TRH-LI corresponding to [I-125]-TRH markers. There was no significant change in hypothalamic and posterior pituitary levels of t-TRH-LI after ovariectomy or orchidectomy. Anterior pituitary levels of t-TRH-LI, however, were increased by an estimated 6-fold after ovariectomy and 2-fold after orchidectomy. After ovariectomy, the proportions of t-TRH-LI accounted for by TRH-LI and EEP-LI were reversed in the female. EEP-LI now accounted for the majority of t-TRH-LI, constituting an increase of approximately al-fold in pituitary EEP-LI levels. The changes in the levels of pituitary TRH-LI and EEP-LI induced by ovariectomy were reversed by 17-beta-estradiol. As in the ovariectomized samples EEP-LI was increased (2-fold) by orchidectomy. Both TRH-LI, which increased 1.6-fold, and EEP-LI were restored to control values after testosterone replacement. These findings confirm the hypothesis that pituitary TRH-LI and EEP-LI are regulated by gonadal status. The fact that these changes were not observed in the hypothalamus and posterior pituitary suggests that TRH-LI and EEP-LI have specific functional significance in the pituitary gland.