INCREASING CONCENTRATIONS OF 17-BETA-ESTRADIOL HAS DIFFERENTIAL-EFFECTS ON SECRETION OF LUTEINIZING-HORMONE AND FOLLICLE-STIMULATING-HORMONE AND AMOUNTS OF MESSENGER-RNA FOR GONADOTROPIN SUBUNITS DURING THE FOLLICULAR PHASE OF THE BOVINE ESTROUS-CYCLE

The hypothesis tested was that 17 beta-estradiol (E(2)) would increase amounts of mRNA for alpha, LH beta, and FSH beta subunits during the follicular phase of the estrous cycle prior to the preovulatory surge of gonadotropins in cows. On Day 16 (Day 0 = estrus) of the estrous cy cle, all cows were treated with prostaglandin F-2 alpha (PGF(2 alpha)) . Cows served as intact controls (CONT, n = 4) were ovariectomized (OV X, n = 5), or were ovariectomized and administered E(2) (OVXE, n = 6) in increasing doses starting at the time of treatment with PGF(2 alpha ). Cows were bled for 6 h before and for 40 h after PGF(2 alpha) treat ment to characterize pulsatile secretion of LH and FSH. Forty hours af ter PGF(2 alpha) treatment, pituitaries were collected for evaluation of amounts of mRNA for alpha, LH beta, and FSH beta subunits. Amplitud e of LH pulses was greater (p < 0.05) in cows from the OVXE than from the CONT group. Concentrations of FSH were greater in cows from both t he OVXE and OVX (p < 0.01) groups than from the CONT group. Amounts of mRNA for alpha and FSH beta subunits were greater (p < 0.01) in pitui taries of cows from the OVX than from the CONT or OVXE groups. Amounts of mRNA for LH beta subunit in pituitaries of cows from the OVX group tended to be greater (p < 0.08) than from the CONT group. Cows in the OVXE group tended (p < 0.08) to have greater amounts of mRNA for FSH beta subunit than did CONT cows. Amounts of mRNA for alpha and LH beta subunits in cows from the OVXE and CONT groups did not differ (p > 0. 10). Pituitary weight and content of LH and FSH were not different (p > 0.10) among cows of the different groups. Ovariectomy resulted in en hanced secretion of gonadotropins and increased amounts of mRNA for go nadotropin subunits above values detected in CONT cows. Ovariectomized cows administered E(2) in follicular-phase patterns had amounts of mR NA for alpha and LH beta similar to those in CONT cows even though sec retion of LH was enhanced in the OVXE group. We reject our hypothesis and conclude that E(2) has a divergent role in regulation of gonadotro pins. Release of LH is enhanced by E(2), but E(2) reduced mRNA for gon adotropin subunits (tended to reduce mRNA for FSH beta subunit) in ova riectomized cows to amounts detected in intact cows during the follicu lar phase of the bovine estrous cycle.