Sex-related differences in pituitary GH-expressing cells induced by hypothyroidism following treatment with methimazole

An immunocytochemical and morphometric study of pituitary GH-expressing cells was carried out in adult rats following chronic treatment with methimazole. The morphological results were correlated to the basal GH serum levels. In both sexes, hypothyroidism induced by methimazolee produced a significant decrease of GH serum levels in relation to untreated animals (p<0.05). Morphometrically, methimazole induced significant decreases in the nuclear area (p<0.05) and in the numerical density of immunoreactive cells (p<0.05). In males, these modifications were accompanied by a significant decrease in cellular and cytoplasmic size (p<0.05), but this was not seen in females. Our results confirm the existence of a physiological stimulatory role of thyroid hormones on the activity of pituitary somatotroph cells that must be modulated by gonadal steroids because the effects of hypothyroidism were more evident in male than in female rats.