LH and FSH subunit mRNA concentrations during the progesterone-induced gonadotropin surge in ovariectomized estrogen-primed immature rats

Progesterone is able to bring about an LH and FSH surge in the estrogen-primed ovariectomized rat while dexamethasone brings about selective FSH release. The purpose of this study was to determine if progesterone and desamethasone-induced gonadotropin secretion is accompanied by changes in LHβ and FSHβ mRNA levels. Gonadotropin α-subunit, LHβ-subunit, and FSHβ-subunit mRNA levels in the pituitary of ovariectomized rats were suppressed by estrogen treatment and dexamethasone brought about a significant increase in FSHβ mRNA within 1 h. Progesterone treatment (0900 h) led to a surge in serum LH levels, with peak values at 1400 h. LHβ mRNA levels were slightly elevated by progesterone at 1400 h. However, an elevation of LHβ at 1400 h was also observed in the dexamethasone group which did not show an increase in serum LH. Serum FSH levels were elevated at 1400 and 1600 h in the progesterone group and at 1600 h in the dexamethasone group after an initial fall at 1000 h. No correlation was observed between increases in serum FSH during these times with FSHβ mRNA levels. In conclusion, the ability of progesterone to induce LH and FSH surges in the estrogen-primed ovariectomized rat was not associated with any clear correlative changes in the mRNAs for these hormones. On the other hand, dexamethasone did increase FSHβ mRNA levels prior to elevating serum levels of FSH. Nevertheless, as a whole, steroid effects on the temporal secretory pattern of LH and/or FSH in the estrogenprimed ovariectomized rat were not mirrored by correlative changes in the mRNA levels for these hormones.