Plasma and Pituitary Concentrations of LH, FSH, and Prolactin in Reproductively Senescent Chinese Hamsters During Various Stages of the Estrous Cycle1

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Abstract
Plasma and pituitary concentrations of LH, FSH, and prolactin (Prl) were determined by radioimmunoassay in young mature (5-6 months old) and aged (17-20 months old) Chinese (C.) hamsters (Cricetulus griseus) during various stages of the estrous cycle. All of the hamsters exhibited a 4-5 day estrous cycle. Both age groups exhibited the same cyclic pattern of circulating LH and FSH concentrations, although the concentrations of LH were substantially higher (P<0.001) in 17-20-month-old C. hamsters, particularly during the LH surge. In contrast, pituitary concentrations of LH were highest (P<0.001) in 5-6-month-old C. hamsters when the two age groups were compared. Concentrations of plasma Prl were out of phase when 5-6- and 17-20-month-old C. hamsters were compared (age-by-time interaction, P<0.01). This discrepancy was most apparent when blood samples were examined, at 6 h intervals, on the evening of ovulation. Since few 17-20 month-old C. hamsters give birth to young, even though they continue to mate (Parkening, 1982), it would appear that age-related changes in the uterus are primarily responsible for loss of fecundity with advancing age.