EFFECTS OF 17-BETA-ESTRADIOL ON DISTRIBUTION OF PITUITARY ISOFORMS OFLUTEINIZING-HORMONE AND FOLLICLE-STIMULATING-HORMONE DURING THE FOLLICULAR PHASE OF THE BOVINE ESTROUS-CYCLE

The objective of this study was to examine the influence of 17 beta-es tradiol (E(2)) on distribution of LH and FSH isoforms during the folli cular phase of the bovine estrous cycle prior to the preovulatory surg es of LH and FSH. On Day 16 of the estrous cycle (Day 0 = estrus), int act controls (CONT; n = 4) were treated with prostaglandin F-2 alpha ( PGF(2 alpha)) to induce luteal regression and initiation of the follic ular phase. Other cows were also treated with PGF(2 alpha) and either ovariectomized (OVX; n = 5) or ovariectomized and given E(2) implants (OVXE; n = 6) to mimic the pattern of increasing E(2) concentrations d uring the follicular phase of the estrous cycle. Pituitaries were coll ected 40 h after treatment with PGF(2 alpha) or ovariectomy (0 h). Ali quots of pituitary extracts were chromatofocused on pH 10.5-4.0 gradie nts. The LH resolved into thirteen isoforms (designated A-L and S, beg inning with the most basic form) while FSH resolved into nine isoforms (designated I-M, beginning with the most basic form). The percentage of LH as isoform F (elution pH = 9.32 +/- 0.01) was greater (p < 0.05) in the OVX group (48.5%) than in the OVXE group (45.0%). LH isoforms I (elution pH = 6.98 +/- 0.01) and J (elution pH = 6.48 +/- 0.01) were more abundant (p < 0.05) in cows from the OVXE (2.3 and 5.8%, respect ively) than the OVX group (1.4 and 3.7%, respectively). Distribution o f LH isoforms in cows from the three groups did not differ (p > 0.10). Distribution of FSH isoforms were similar (p > 0.05) among all groups . In summary, removal of the ovary (OVX) resulted in a slight increase in percentage of the basic LH isoform F, while removal of the ovary a nd administration of E(2) (OVXE) in a pattern that mimicked increasing concentrations of E(2) during the follicular phase of the estrous cyc le resulted in a slight increase in the percentage of acidic LH isofor ms (I and J). There was no influence of ovariectomy or treatment with E(2) on distribution of FSH isoforms in the pituitary. Thus, gonadotro pin heterogeneity does not appear to change significantly during the f ollicular phase of the bovine estrous cycle.