Modification of ovulatory mechanisms by postnatal administration of estrogen to the rat

The current studies have demonstrated that the single injection of 100 µg estradiol benzoate to 5-day-old female rats results in permanent sterility. When adult, these rats exhibit anovulatory vaginal cycles in which the stage of vaginal cornification predominates; they mate, but not in correlation with the vaginal cycle. Ovulation is not induced by mating or by progesterone injections, and only infrequently following electrical stimulation of the hypothalamus. By varying the amount of estrogen administered it was found that 5 µg is the minimal dosage capable of inducing this sterility syndrome. These and other data suggest that the female pattern of cyclic release of gonadotrophins differentiates in the absence of significant estrogen titers.