Biology of Reproduction, Vol 25, 825-831, Copyright © 1981 by Society for the Study of Reproduction

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

¹ Department of Anatomy, The University of Texas Medical Branch at Galveston, Galveston, Texas 77550.

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.

Note:
ACKNOWLEDGMENTS Materials for the RIA of LH, FSH, and Prl were kindly supplied by Dr. A. F. Parlow and the NIAMDD Pituitary Hormone Distribution Program. We thank Dr. H. Bunce, Biostatistics and Academic Computation Center, for the statistical analysis of the data.