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 maleWistar rats. To confirm hypo- and hyper-thyroidism, the concentration of plasma thyroid hormones wereassayed by radioimmunoassay. The hypothyroid state, induced by administration of 25 mg/kg/daymethimazole for 5 successive days, resulted in significant decrease in the number of Sertoli cells, spermcount, Leydig cells and the diameter of seminiferous tubules. The hyperthyroid state, induced byadministration 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 andtestosterone were also evaluated. Hypo- and hyper-thyroidism had no effects on the concentrations of FSHand LH, while the concentration of testosterone was significantly increased in hyperthyroid state; it decreasedin hypothyroid state in comparison with the control euthyroid rats. In conclusion, our data indicated thathypo- and hyper-thyroidism affect spermatogenesis through their effects on germinal, interstitial and Sertolicells but not through the pituitary-gonadal axis.