253 THE MARE MODEL FOR LUTEINIZED UNRUPTURED FOLLICLE SYNDROME: INTRAFOLLICULAR ENDOCRINE MILIEU

Abstract

Mechanisms underlying the development of luteinized unruptured follicle (LUF) syndrome in mares were studied to provide a model for human anovulation. The aims of the present study were (1) to determine the effect of recombinant equine LH (reLH) and prostaglandin F2α (PGF2α) on LUF formation (Experiment 1), (2) to identify an optimal dose of COX-2 inhibitor (flunixin-meglumine; FM) required to experimentally induce LUF (Experiment 2), and (3) to evaluate the intrafollicular endocrine milieu in induced LUF (Experiment 3). In Experiment 1, mares (n = 30) were treated with reLH from Days 7 to 15 (Day 0 = ovulation), with PGF2α on Day 7 or in combination. In Experiment 2 (n = 18 mares), FM at doses of 2.0 or 3.0 mg kg–1 every 12 h and hCG (1500 IU) were administered after a follicle ≥32 mm was detected. In Experiment 3 (n = 23 mares), FM at a dose of 2.0 mg kg–1 every 12 h plus hCG was used to induce LUF and investigate the intrafollicular endocrine milieu. Shapiro-Wilk tests were used for analysing data for normal distribution, and data not normally distributed were transformed to ranks before any further analyses. For sequential data, mixed model repeated-measures ANOVA were used. For single-point data, Student’s t-tests were used. No LUF were induced in mares treated with reLH or PGF2α, in combination or separately. However, LUF were induced in 100% of mares using FM at the dose rate of 2.0 and 3.0 mg kg–1 of body weight in combination with 1500 IU of hCG. Intrafollicular PGF2α metabolite (PGFM), PGF2α, and prostaglandin E2 (PGE2) were lower, and the ratio of PGE2 : PGF2α was higher in induced LUF. Higher levels of intrafollicular growth hormone, cortisol, oestradiol, testosterone, and total primary sex steroids were observed in the induced LUF group; however, LH, prolactin, vascular endothelial growth factor-A, and nitric oxide did not differ between the control and induced LUF groups. In conclusion, COX-2 inhibitors used in conjunction with hCG can be used to pharmacologically induce LUF with 100% success in mares. This study revealed part of the intrafollicular endocrine milieu and the association of prostaglandins in LUF formation. We postulated that LUF result from decreased intrafollicular prostaglandin concentrations or altered prostaglandin synthesis, as indicated by disparity in PGE2 : PGF2α ratio. Increased intrafollicular oestradiol, testosterone, cortisol, and growth hormone were associated with LUF formation; however, further studies are necessary to ascertain the cause-effect relationship. The effect of LH on LUF formation remains unclear. This study further encourages the use of intrafollicular v. systemic biomarkers for evaluating ovulatory disorders. Finally, results from this study support the use of the mare as a model for investigating the poorly understood LUF syndrome in women.