Sex steroids regulate TSH-induced thyroid growth during sexual maturation in Wistar rats

Sex steroids have been reported to influence thyroid pathogenesis in human and experimental animals. However, there is no much report on the effect of sex steroids in the growth of normal thyroid. The present study is an attempt to know TSH-induced thyroid growth during sexual maturation in Wistar rats. Wistar rats of day 1 to day 150 postpartum (pp) were used in the present study. Thyroid growth indices such as absolute and relative thyroid weights, concentration of DNA in the thyroid, mitotic index and numerical density of thyrocytes, hormonal profiles in the serum and thyroid tissue such as thyrotropin (TSH), thyroid hormones, testosterone and estradiol, and receptors for TSH, androgen and estrogen in the thyroid were estimated. A gender-specific shift in the pattern of serum TSH and TSH-R was observed during 30-45 days of postnatal life, the period at which steroidogenesis by testes or ovaries of rats are reactivated. Testosterone in males and estradiol in females modulate thyroid growth through TSH. It is concluded from the present study that changes in the sex steroid status between male and female rats have a definite influence on the pattern of thyroid growth and TSH.