Effect of the Interaction of Body Weight and Daily Estradiol Benzoate Injections on the Onset of Estrous Cyclicity in Rats

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Abstract
In immature female rats daily injections of 0.1 µg estradiol benzoate (EB) per 100 g BW begun at weaning (21 days of age) and terminated on the day of vaginal opening induced a single precocious period of vaginal cornification (estrus). The second estrous period, however, came at the same age and body weight as the first spontaneous estrus in oil-injected controls, and the length of the first estrous cycle was significantly longer in EB-treated animals than in controls. Body weight was varied by raising animals in different-sized litters to allow an examination of the effect of weight on the timing of the first two estrous periods. This analysis indicated that weight contributed a similar amount of variance to the age at the second estrus in the EB-treated group and the first estrus in the control group, but much less variance to the age at first estrus in EB-treated animals. These data were interpreted as support for the hypothesis that EB-treatment does not trigger "true precocious puberty," and that the first spontaneous estrous period in EB-conditioned animals occurs at the normally scheduled age and body weight.

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