title: Interactions of follicular factors and season in the regulation of circulating concentrations of gonadotrophins in mares.
abstract: Follicle growth and associated changes in circulating hormone concentrations were evaluated after follicle ablation in mares (n = 13) during four 13 day periods beginning at means of -98.5, -61.4, -26.0 and 10 days from the first ovulation and corresponding to mid-anovulatory, early-transitional, late-transitional and ovulatory periods, respectively. During each period, all follicles > 5 mm in diameter were ablated (day 0) followed by no subsequent ablations (all-follicle group) or the ablation of all follicles > 5 mm when a new follicle reached > 10 mm (0-follicle group). A follicular wave emerged at means of days 1.5-2.5 in all mares of the all-follicle group during each period. Follicle activity increased between the mid-anovulatory and the transitional periods, as indicated by increases in the diameter of the largest follicle and the number of follicles in the all-follicle groups; nonetheless, there were no differences in the FSH concentrations of the wave-stimulating surge throughout the study. Circulating total inhibin increased between day 3 and day 6 in the all-follicle groups but not in the 0-follicle groups, and was higher during the late-transitional and ovulatory periods than during earlier periods in the all-follicle groups. In the all-follicle groups, circulating FSH decreased between day 3 and day 6. In the 0-follicle groups, FSH did not decrease and was higher during the late-transitional and ovulatory periods than during the mid-anovulatory period. Circulating LH was higher during the late-transitional and ovulatory periods than during earlier periods and was not different between the all-follicle and 0-follicle groups. On the basis of temporal relationships, it was concluded that the follicles of a wave secreted inhibin during all periods and the follicular inhibin suppressed circulating FSH. An increase in circulating inhibin induced by the growth of follicles > 21 mm in diameter during the late-transitional and ovulatory periods counteracted a stimulatory effect on FSH mediated by season.
authors.affiliation: Department of Animal Health and Biomedical Sciences, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: F X
authors.initials: FX
authors.lastname: Donadeu
authors.forename: O J
authors.initials: OJ
authors.lastname: Ginther
mesh_terms: D000818:Animals; D004971:Estrus / Q000502:physiology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D006065:Gonadotropins, Pituitary / Q000097:blood*; D006736:Horses / Q000097:blood*; D007265:Inhibins / Q000032:analysis; D007986:Luteinizing Hormone / Q000097:blood; D006080:Ovarian Follicle / Q000502:physiology* / Q000601:surgery; D012621:Seasons
chemical_list: D006065:Gonadotropins, Pituitary; D007265:Inhibins; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone