Measurement of the amount of mRNA for gonadotropins during an estradiol-induced preovulatory-like surge of LH and FSH in ovariectomized ewes

Abstract

The amount of messenger RNA (mRNA) for luteinizing hormone β-subunit (LHβ), follicle-stimulating hormone β-subunit (FSHβ) and α-subunit was measured during estradiol-17β (E) positive feedback in ovariectomized (OVX) ewes. During the anestrous season, OVX ewes were given an i.m. injection of E (25 μg: n=5) or oil (control; n=4) and hourly blood samples were collected for 16 hr. After blood collection, ewes were killed and anterior pituitary glands were removed for analysis of hormone and mRNA content. Preovulatory-like increases in serum concentrations of LH and FSH were measured in E-treated OVX ewes. In two E-treated OVX ewes the serum concentrations of LH and FSH were still increasing, whereas in the remaining three E-treated OVX ewes, serum concentrations of LH were on the decreasing portion of the E-induced preovulatory-like surge. Pituitary content of LH was lower (P<.10) in E-treated OVX ewes when serum concentrations of LH were decreasing than that measured in control ewes or E-treated OVX ewes in which serum concentrations were still increasing. Pituitary content of FSH and prolactin were similar (P>.05) among all groups. The amount of mRNA for LHβ-subunit was similar (P>.05) in ewes in which serum concentrations of LH were increasing and in control ewes, but was lower (P<.05) in ewes with decreasing levels of LH. The amount of mRNA for FSHβ-subunit was lower (P<.05) in all E-treated OVX ewes (independent of whether serum concentrations of FSH were increasing or decreasing) than that measured in control ewes. There was no difference (P>.05) in the amount of mRNA for α-subunit among any groups. Thus, amounts of mRNA for the β-subunits of gonadotropins are reduced, while amounts of mRNA for α-subunit are unchanged during estradiol positive feedback in OVX ewes.