Date Approved


Graduate Degree Type


Degree Name

Biomedical Sciences (M.H.S.)

Degree Program

Biomedical Sciences

First Advisor

Christopher Pearl

Second Advisor

Dan Bergman

Third Advisor

Dawn Richiert

Academic Year



Estrogens, in addition to testosterone, are physiologically relevant to normal sperm production in the testis and sperm maturation in the epididymis. Previous studies from our lab demonstrated that daily sperm production declines from 15 to 18 months of age in Sprague Dawley rats, and treatment with estrogen during this period attenuated the age-associated decline. Phytoestrogens are present in standard rodent diets at high levels (350-650 mg/kg) and may be potential endocrine disruptors. The purpose of this study was to investigate the effect of removing dietary phytoestrogens during aging on sperm production. Retired breeder Sprague Dawley rats were obtained at 9 months of age, divided into three groups and further housed until 15 or 18 months of age. At 15 months of age, one group of animals was switched to a low phytoestrogen (0-20 mg/kg) rodent chow. A second group of animals was maintained on the high phytoestrogen diet. Groups one and two were maintained on their respective diets for three months until they were 18 months old. At 18 months of age, animals were euthanized and reproductive tissues were collected for analysis. The third group of animals was euthanized and tissues collected at 15 months of age. Results show that daily sperm production in both 18 month groups declined approximately 23% compared to animals 15 months of age, but was not different based on diet. The number of Sertoli cells decreased with age by about 21%, but the decrease was not affected by dietary phytoestrogens as cell numbers in both 18-month old groups were similar. Interestingly, concentrations of testosterone were not significantly different between ages or with dietary phytoestrogen content. However, there was a decrease in serum (~37%) and testicular (~42%) estradiol concentrations with age. Collectively these results further support the hypothesis that sperm production decreases with age, and the relationship between estradiol and Sertoli cells helps to maintain fertility. The findings also suggest that removal of dietary phytoestrogens does not affect the age-related decline in efficiency of spermatogenesis and daily sperm production.