Ovarian folliculogenesis and steroidogenesis were studied in hyperthyroid adult rats. Hyperthyroidism was induced in 27 five month-old Wistar rats by daily administration of 50µg L-thyroxin. Other 27 rats were maintained in euthyroid state as controls. At 30, 60 and 90 days after the beginning of the treatment, nine rats from each group were sacrificed. The ovaries were weighed, inspected and processed for histomorphometric evaluation. Plasmatic levels of free T4, estradiol and progesterone were determined. The levels of T4 were significantly higher in the hyperthyroid rats at 30, 60 and 90 days, but significant differences on the ovarian weight were detected only at 90 days. The number of secondary and tertiary follicles and of corpus luteum was greater at 60 or 90 days, but the rate of follicular atresia was different only at 90 days. No significant differences were observed on the number of primary and pre-ovulatory follicles and on the concentrations of estradiol and progesterone. Our data suggest that hyperthyroidism stimulates ovarian folliculogenesis in sexually mature rats. Furthermore, there is a reduction on the rate of follicular atresia.
Rat; Hyperthyroidism; Ovary; Folliculogenesis; Steroidogenesis
