Impaired Preparturitional Rise of Plasma Estradiol in Aging C57BL/6J Mice1

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Abstract
The preparturitional rise of plasma estradiol (E2) was delayed and reduced in aging (11-12 mo. old) C57BL/6J mice. In young mice (3-7 mo. old), plasma E2 increased up to 3-fold after day 17 of pregnancy, whereas in older mice than E2 increase was delayed by 1 day or more and never reached the E2 levels of young mice. During days 1-17, no age differences in E2 were detected. The normal preparturitional decrease of plasma progesterone (P) was slowed in the same older mice studied here. The impaired regulation of E2 and P may be factors in the 2 day (mean) prolongation of pregnancy observed in these older mice.