Effects of 17β-Estradiol on Distribution of Pituitary Isoforms of Luteinizing Hormone and Follicle-Stimulating Hormone during the Follicular Phase of the Bovine Estrous Cycle1

The objective of this study was to examine the influence of 17 beta-estradiol (E2) on distribution of LH and FSH isoforms during the follicular phase of the bovine estrous cycle prior to the preovulatory surges of LH and FSH. On Day 16 of the estrous cycle (Day 0 = estrus), intact controls (CONT; n = 4) were treated with prostaglandin F2 alpha (PGF2 alpha) to induce luteal regression and initiation of the follicular phase. Other cows were also treated with PGF2 alpha and either ovariectomized (OVX; n = 5) or ovariectomized and given E2 implants (OVXE; n = 6) to mimic the pattern of increasing E2 concentrations during the follicular phase of the estrous cycle. Pituitaries were collected 40 h after treatment with PGF 2 alpha or ovariectomy (0 h). Aliquots of pituitary extracts were chromatofocused on pH 10.5-4.0 gradients. The LH resolved into thirteen isoforms (designated A-L and S, beginning with the most basic form) while FSH resolved into nine isoforms (designated I-IX, 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%, respectively) than the OVX group (1.4 and 3.7%, respectively). Distribution of LH isoforms in cows from the three groups did not differ (p > 0.10).(ABSTRACT TRUNCATED AT 250 WORDS)