Effects of Prolonged Dietary Exposure to Phytoestrogens on Spermatogenesis and Testis Development of Rats
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The mammalian testis supports the process of spermatogenesis, which is sperm cell production. Spermatogenesis occurs within Sertoli cells in the seminiferous tubules and its duration is 51.6 days. Endogenous estrogen expression is essential for maintaining normal spermatogenesis. Phytoestrogens are plant-derived endocrine disruptor compounds. They have high affinity for estrogen receptors (ERs) and can compete with endogenous estrogens to promote or inhibit estrogen like responses. Humans are most commonly exposed to phytoestrogens through modern diets containing soybean-derived foods that are rich in isoflavanoids like tofu, soybean milk, and soy-based infant formulas. The effects of phytoestrogen exposure on spermatogenesis are not well understood, which is why there are reports on both their beneficial and adverse effects on the male reproductive system. However, many studies have shown that even minimal disturbances of endogenous endocrine function during the stages of critical development can lead to reductions in testis weight and in the amount and quality of sperm produced in both rodents and humans. The most likely route of exposure of phytoestrogens to humans is through dietary intake at or close to natural dose levels, typical of modern diets. Additionally, it is more likely that humans will change their dosage of phytoestrogen intake in small increments rather than dramatically increasing or decreasing their phytoestrogen intake. The objective of the present study was to better simulate real world human exposure to phytoestrogens by exposing Brown Norway rats, previously raised on a medium dose of dietary phytoestrogens from birth to 88 days old (pre-treatment control group), to either low, continuation of medium, or high dosages of dietary phytoestrogens (treatment groups) until 153 days old. It was hypothesized that this method of phytoestrogen exposure would result in differences in spermatogenesis and testis development between the rats in the pre-treatment control group and the rats in the three treatment groups as well as among the rats in the three treatment groups.