Biol Reprod Keystone Symposia Conference on Frontiers in Reproductive Biology & Regulation of Fertility.
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Biology of Reproduction, Vol 22, 751-758, Copyright © 1980 by Society for the Study of Reproduction

Serum Progesterone During Pregnancy and Pseudopregnancy and Gestation Length in the Aging Rat

ANNA E. MILLER 1, and GAIL D. RIEGLE 1

1 Endocrine Research Unit, Department of Physiology and Department of Animal Husbandry, Michigan State University, East Lansing, Michigan 48824


The hypothesis that reduced secretion of progesterone by corpora lutea contributes to reproductive failure in aged mammals was tested in aging Long-Evans rats. The effect of age on serum progesterone during pregnancy and pseudopregnancy was studied in separate groups of rats with normal ovarian cycles at 4, 7, 9, 11, 13, 15, 20 and 22 months of age. Progesterone was also measured in constant estrous rats made pseudopregnant by mating at 11, 15, 20 and 22 months of age. Mated rats were divided into subgroups based on whether they produced litters. Successful pregnancy was reduced to 50% of the 11-months-old and 25% of the 13-month-old rats with no successful pregnancies occurring in older rats. Progesterone was assayed from serial blood samples collected on Days 1, 6, 11 and 16 after mating. Average progesterone concentrations on any particular day of pregnancy or pseudopregnancy were not affected by increased age. Progesterone was increased on postcoital Days 6 and 11 in all groups. Average progesterone concentrations on postcoital Days 1, 6 and 11 were similar in the groups with ovarian cycles which produced litters, the groups with ovarian cycles which did not produce litters and in the mated constant estrous groups which did not produce litters. However, progesterone concentration was higher in the pregnant groups than in the pseudopregnant groups on postcoital Day 16. The length of gestation was progressively increased from 22.2 days in the 4-month-old group to 23.7 days in the 13-month-old group.

A second experiment considered the effect of age on serum progesterone during early and late gestation in 4-month-old compared with 13-16-month-old rats. Progesterone was measured from serial blood samples collected from Days 1 to 5 and from Days 19 to 22 of pregnancy. Progesterone was similarly increased on postcoital Days 1 through 5 in young and aged groups. Average progesterone concentration was progressively decreased from Days 19 to 22 of pregnancy in groups producing litters. The aged group had higher progesterone on Day 22 of pregnancy than did the young group. The higher progesterone concentration on Day 22 of pregnancy in the aged group was consistent with the increased length of gestation in this group (22.9 days) compared with that in the young rats (22.1 days). The results of these experiments suggest no significant effect of age on progesterone secretion by corpora lutea during early pregnancy or pseudopregnancy in the rat and indicate that uterine failure may contribute to the loss of fertility in the aging rat.

 Submitted on October 1, 1979
Accepted on January 16, 1980






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Copyright © 1980 by the Society for the Study of Reproduction.