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Changes in systemic concentrations of FSH, LH, oestradiol and progesterone during the ovulatory follicular wave were compared between 30 mares and 30 women. Based on a previous study, the emergence of the future ovulatory follicle was defined as occurring at 13.0 mm in mares and 6.0 mm in women, and deviation in diameter between the two largest follicles was expected to begin at 22.7 mm in mares and 10.3 mm in women. Mean FSH concentrations were high in mares during the luteal phase, resulting from statistically identified FSH surges occurring in individuals on different days and in different numbers (mean, 1.5 ± 0.2 surges/mare); the internadir interval was 3.9 ± 0.3 days. In contrast, mean FSH in women was low during the luteal phase and increased to a prolonged elevation during the follicular phase. The prolonged elevation was apparent in each individual (internadir interval, 15.2 ± 0.4 days). Changes in LH or oestradiol concentrations encompassing deviation were not detected in mares, but both hormones increased slightly but significantly between emergence and deviation in women. The hypothesis that a greater number of growing follicles causes a greater predeviation decrease in FSH was supported for mares (r, −0.39; P< 0.04), but a similar negative correlation (r, −0.36) was not significant in women. The hypothesis that the increase in oestradiol during the luteal phase in women was at least partly attributable to luteal-phase anovulatory follicular waves was not supported. Normalization of FSH concentrations to the day of emergence showed maximum value on the day of emergence with a significant increase and decrease on each side of emergence in both species. The day of expected deviation occurred 3 days after emergence during the decline in FSH in both species. These results indicated that the previously reported striking similarities in emergence and deviation between mares and women during the ovulatory follicular wave are associated with species similarities in the temporal relationships between follicle events and FSH concentration changes. Thus, mares may be useful research models for studying the role and mechanism of the action of FSH in emergence and deviation during the ovulatory follicular wave in women.

Luteinized unruptured follicle (LUF) syndrome is a recurrent anovulatory dysfunction that affects up to 23% of women with normal menstrual cycles and up to 73% with endometriosis. Mechanisms underlying the development of LUF syndrome in mares were studied to provide a potential model for human anovulation. The effect of extended increase in circulating LH achieved by administration of recombinant equine LH (reLH) or a short surge of LH and decrease in progesterone induced by prostaglandin F₂α (PGF₂α) on LUF formation (Experiment 1), identification of an optimal dose of COX-2 inhibitor (flunixin meglumine, FM; to block the effect of prostaglandins) for inducing LUFs (Experiment 2), and evaluation of intrafollicular endocrine milieu in LUFs (Experiment 3) were investigated. In Experiment 1, mares were treated with reLH from Day 7 to Day 15 (Day 0=ovulation), PGF₂α on Day 7, or in combination. In Experiment 2, FM at doses of 2.0 or 3.0 mg/kg every 12 h and human chorionic gonadotropin (hCG) (1500 IU) were administered after a follicle ≥32 mm was detected. In Experiment 3, FM at a dose of 2.0 mg/kg every 12 h plus hCG was used to induce LUFs and investigate the intrafollicular endocrine milieu. No LUFs were induced by reLH or PGF₂α treatment; however, LUFs were induced in 100% of mares using FM. Intrafollicular PGF₂α metabolite, PGF₂α, and PGE₂ were lower and the ratio of PGE₂:PGF₂α was higher in the induced LUF group. Higher levels of intrafollicular E2 and total primary sex steroids were observed in the induced LUF group along with a tendency for higher levels of GH, cortisol, and T; however, LH, PRL, VEGF-A, and NO did not differ between groups. In conclusion, this study reveals part of the intrafollicular endocrine milieu and the association of prostaglandins in LUF formation, and indicates that the mare might be an appropriate model for studying the poorly understood LUF syndrome.