Induction of persistent diestrus followed by persistent estrus is indicative of delayed maturation of tonic gonadotropin-releasing systems in rats.

Abstract

The relationship between the amount and duration of administration of estradiol benzoate (EB) to newborn female rats and the induction of sterility was examined in 407 animals. Vaginal smear patterns were classified into 3 types according to the incidence of vaginal proestrus and estrus over a 10-day period: persistent estrous (PE), persistent diestrus (PD), and intermediate (INT), so that the changes in vaginal smear patterns could be analyzed quantitatively. Incidence of the PE pattern was most frequent in the rats that received a single injection of 10 micrograms EB on the day of birth (Day 1). Almost all of the animals receiving 10 daily injections of 10 micrograms EB from Day 1 showed persistent diestrus until at least 100 days of age. In the rats that were given 5 daily injections of 10 micrograms EB Day 1 through Day 5, or a single injection of 100 micrograms EB on Day 3, the incidence of the PD pattern was high at 41-60 days of age, but later the PD-type was replaced by the PE pattern of vaginal smears. In the rats that were treated with 5 daily injections of 10 micrograms EB from Day 1 through Day 5 and were ovariectomized on Day 22, a slight but significant increase in the level of luteinizing hormone in plasma was noted after administration of EB and progesterone on Day 100 but not on Day 50. These results indicated that neonatal injections of EB induce sterility, but the effect is dependent on the amount of EB injected and length of time over which the injections are given.(ABSTRACT TRUNCATED AT 250 WORDS)