Histomorfometria e função tireoidiana no ciclo estral da rata / Histomorphometric and functional studies of the rat thyroid throughout the estrous cycle

ABSTRACT

The influence of the estrous cycle on the thyroid gland was studied. Twenty one five-to-seven-month-old Wistar female rats were divided according to the stage of the estrous cycle in two groups metaestrus-diestrus and proestrus-estrus. After gross inspection, the thyroids were weighed, sampled, and processed for staining with hematoxilyn-eosin. Seric concentrations of total T4, free T4, total T3, TSH, progesterone, and estradiol were measured. The values of estradiol were significantly higher in the proestrus-estrus stage. However, no significant differences in the plasmatic concentrations of progesterone, free T4, total T4 and TSH throughout the cycle were found. The results of the morphometric study of the thyroid did not indicate any significant differences between the groups. These findings suggest that there is no thyreotrophic effect of estrogen during the estrous cycle in rats.(AU)