Ovulation in rats is delayed by a substituted triazole

When a single oral dose of 5 or 25 mg/kg of the substituted triazole R151885 [1,1-di(4-fluorophenyl)-2-(1,2,4-triazol-1-yl)-ethanol] was administered at midday on diestrus-2 to rats with regular 4-day estrous cycles, the subsequent ovulation was delayed by 24 or 48 hr, respectively. There was no evidence of toxicity at the doses used. The only morphological changes detected in the reproductive tract were a delay in accumulation of uterine fluid and prolonged but normal follicular maturation prior to the delayed ovulation. The delayed follicles were slightly larger than normal follicles at the time of ovulation. The preovulatory peak plasma concentrations of progesterone, follicle stimulating hormone (FSH), and luteinizing hormone (LH) were delayed by 24 hr in rats treated with 5 mg/kg of R151885 on diestrus-2. Although there was a normal preovulatory peak plasma concentration of estradiol, values were reduced by between 30 to 50% late on diestrus-2 and early on proestrus. Additionally, in ovariectomized rats, 3 daily doses of 25 mg/kg of R151885 antagonized the action of estradiol on the uterus by 45%. We suggest that the reductions in plasma estradiol concentrations during diestrus-2 and proestrus, combined with some antagonism of estradiol's action, may prevent adequate priming of the pituitary thereby suppressing the preovulatory LH surge required for ovulation. The suppression of this LH surge is of a temporary nature indicating a reversible effect of R151885 on the hormonal control system.