Testosterone and estradiol differentially regulate TSH-induced thyrocyte proliferation in immature and adult rats.

Though sex steroids are found to influence thyroid pathogenesis in human and in animals, their role in normal thyroid growth and thyrocyte proliferation is not yet understood fully. The present study is addressed to know the effect of testosterone and estradiol on the basal and TSH-induced thyrocyte proliferation in immature and adult rats in vitro. The male and female Wistar rats were gonadectomized (GDX) and one group of GDX rats were supplemented with either testosterone or estradiol. After the experimental period, the rats were sacrificed by decapitation and thyroid glands were removed, washed in Hank's Balanced Salt Solution (HBSS), pH 7.4 and digested with the enzyme mixture containing 0.08% collagenase and 0.12% dispase in HBSS. The isolated follicles were washed thrice with Dulbecco's modified Eagle's medium (DMEM) containing 0.5% fetal bovine serum (FBS), and were cultured in Falcon's tissue culture flasks containing 5 ml DMEM with FBS (5%) transferrin (5 microg/ml), hydrocortisone (10(-8) M), somatostatin (10 microg/ml), insulin (10 microg/ml) and glycyl-L-histidyl-L-lysine acetate (10 microg/ml). The cells (2.5 x 10(4)) were exposed to various exponential doses of TSH or testosterone (6.25-800 ng/ml) or estradiol (6.25-800 pg/ml). It is suggested from the present study that both TSH and sex steroids enhance thyrocyte proliferation. The mitogenic effect of TSH is greater than that of sex steroids. Sex steroids modulate TSH-induced cell proliferation in a gender-specific manner.