The effect of thyroid activity on adult rat spermatogenesis

The influence of hypo- and hyper-thyroidism on spermatogenesis was studied in 60-day-old adult male Wistar rats. To confirm hypo- and hyper-thyroidism, the concentration of plasma thyroid hormones were assayed by radioimmunoassay. The hypothyroid state, induced by administration of 25 mg/kg/day methimazole for 5 successive days, resulted in significant decrease in the number of Sertoli cells, sperm count, Leydig cells and the diameter of seminiferous tubules. The hyperthyroid state, induced by administration of 1 mg/kg/day L-thyroxine for 10 successive days, increased the number of Sertoli cells, sperm count, Leydig cells and the diameter of seminiferous tubules. Serum levels of FSH and LH and testosterone were also evaluated. Hypo- and hyper-thyroidism had no effects on the concentrations of FSH and LH, while the concentration of testosterone was significantly increased in hyperthyroid state; it decreased in hypothyroid state in comparison with the control euthyroid rats. In conclusion, our data indicated that hypo- and hyper-thyroidism affect spermatogenesis through their effects on germinal, interstitial and Sertoli cells but not through the pituitary-gonadal axis.