Circulating Plasma Levels of Pregnenolone, Progesterone, Estrogen, Luteinizing Hormone, and Follicle Stimulating Hormone in Young and Aged C57BL/6 Mice During Various Stages of Pregnancy

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Abstract
Young (3-5 mo of age) and senescent (12-15 mo of age) multiparous C57BL/6 mice were mated with young males (3-6 mo of age) and the numbers of preimplantation embryos and implantation sites determined on days 1 (day of plug), 4, 9, and 16 of pregnancy. The numbers of viable embryos were significantly lower (p ≤ 0.02 to p ≤ 0.001) in senescent females compared with young females on all days except day 1 of pregnancy. Plasma samples tested by radioimmunoassay indicated circulating estradiol-17b was significantly lower (p ≤ 0.05) on day 1 and higher (p ≤ 0.05) on day 4 in older females, whereas FSH was higher on days 4, 9, and 16 (p ≤ 0.02 to p ≤ 0.001) in senescent females when compared with samples from young females. Levels of pregnenolone, progesterone, estrone, and LH were not significantly different at any stage of pregnancy in the two age groups. From the hormonal data it did not appear that degenerating corpora lutea were responsible for the declining litter size in this strain of aged mouse.