EFFECT OF HYPOTHYROIDISM ON OVARIAN FOLLICULAR DEVELOPMENT, GRANULOSA-CELL PROLIFERATION AND PERIPHERAL HORMONE LEVELS IN THE PREPUBERTAL RAT

The aim of this study was to examine the effects of prepubertal hypoth yroidism on ovarian development in rats. Therefore, from birth up to d ay 40 postpartum, rats were given 6-propyl-2-thiouracil (PTU) via the drinking water of mothers and pups. At ages ranging from 12 to 40 days , ovarian weights were measured and serum was collected to estimate th yrotrophin (TSH), follicle-stimulating hormone (FSH) and inhibin level s. Two hours before sacrifice the animals received an injection of bro modeoxyuridine (BrdU) to estimate the proliferative activity of the fo llicular granulosa cells. Ovaries were fixed in Carnoy's fluid and fol licle counts were performed on sections stained with anti-BrdU and wit h haematoxylin and eosin. The PTU treatment resulted in increased seru m TSH levels, indicative of hypothyroidism, and markedly lower body an d ovarian weights, whereas serum FSH and inhibin levels were hardly af fected. At day 40, ovaries of PTU-treated animals contained relatively more secondary and less antral follicles, smaller non-atretic antral follicles and more atretic follicles when compared with untreated rats , while corpora lutea were absent. It is concluded that this disturbed folliculogenesis is due to inadequate thyroid hormone supply, which h ampers the differentiation and not the proliferation of granulosa cell s because diameters of antral follicles were significantly smaller whe reas the BrdU-labelling index had not changed.