Hypogonadism and thyroid function in hyper and euthyroid rats

The effects of hypogonadism on thyroid function of hyper and euthyroid rats were measured based on plasmatic profile of thyroid hormones, ovarian steroids, TSH and thyroid histomorphometry. A group of five-month-old ovariectomized Wistar rats were maintained at hyper or euthyroid state for 30, 60 and 90 days. A group of non castrated was used as control. The hyperthyroidism was induced by gastric infusion of L-tiroxin 50µg daily. At the end of each period nine rats of each group were sacrificed, the blood plasma collected and the thyroid inspected, measured and processed for histomorphometric analyses. In blood plasma the concentrations of estradiol, progesterone, total and free tiroxin, total and free T3 and TSH were determined. The hypogonadism did not alter the values of free T3 and TSH but was able to rise free tiroxin in both hyper and euthyroid states. Total tiroxin levels were affected by castration, but only in the hyperthyroid state. Folicular epithelium height presented variations along the experiment in euthyroid individuals although these did not influence thyroid weight. No correlations between estrogen and any other variables were observed, but the progesterone levels were conversely proportional to the total and free tiroxin levels. It was concluded that hypogonadism alter the histomorphometric patterns of thyroid gland in euthyroid individuals, rise the plasmatic levels of free tiroxin regardless the functional state of thyroid gland and powered the total tyroxin rise in hyperthyroidism, probably due to the influence of hypoprogesteronism but not to the hypoestrogenism.

Rat; hypogonadism; hyperthyroidism; euthyroidism; thyroid