Steady-State Amounts of α- and Luteinizing Hormone (LH) β-Subunit Messenger Ribonucleic Acids Are Uncoupled from Pulsatility of LH Secretion during Sexual Maturation of the Heifer

Our primary objective for this study was to determine whether steady-state amounts of α - and LH β-subunit mRNAs in the anterior pituitary are altered during sexual maturation in the bovine female. A secondary objective was to determine whether 17β-estradiol (E2) alters amounts of LH subunit mRNAs before onset of puberty. Heifers (7 mo old) were assigned to one of three treatments: 1) ovariectomized (OVX, n = 16); 2) OVX and administered E2 (OVXE, n = 16); or 3) ovary-intact (INTACT, n = 20). Pituitaries were collected at an estimated 120 days before onset of puberty (prepuberty) or 25 days before onset of puberty (peripuberty). Six INTACT heifers were used to determine time of puberty during the experimental period, and their pituitaries were collected 40 h after administration of prostaglandin F2α,. (postpubertal INTACT group). Relative amounts of mRNAs for LH subunits in each pituitary were determined by Northern analysis and scanning densitometry. Amounts of α- and LH β- subunit mRNAs were lower in pituitaries of INTACT heifers and OVXE heifers, regardless of stage of sexual maturation, than in those of OVX heifers. Amounts of a-subunit mRNA were similar in OVXE and INTACT heifers regardless of stage of sexual maturation. Amounts of LH β-subunit mRNA did not change during sexual maturation in heifers in the INTACT group. Concentrations of E2 were higher and LH β-subunit mRNA were lower in heifers from the prepubertal OVXE group than in heifers in all other treatment groups. We conclude that steady-state amounts of a- and LH β-subunit mRNAs are not limiting during sexual maturation in the bovine female. However, when concentrations of E2 are elevated during the prepubertal period to those typical of the follicular phase of the bovine estrous cycle, levels of LH β-subunit mRNA are specifically suppressed