Effects of Thyroid Hormone on Some Uterine Responses to Estrogen*

Uterine edema induced by 0.1 microgram 17 beta-estradiol (E2)/100 g BW, as well as uterine eosinophilia induced by 0.01, 0.1, 1, 10, and 30 micrograms E2/100 g BW, decrease in the presence of 20 micrograms T3 or T4/100 g BW in the immature rat. Estrogen binding by uterine eosinophils and the number of eosinophils in the blood also decrease with T3 or T4, suggesting an explanation for the findings in the uterus. Thyroid hormones alone or in the presence of 0.001, 0.01, 0.1 and 1 microgram E2/100 g BW, increase the uterine RNA content 7 h after administration compared with the same doses of E2 alone. This response is not associated with any further increase in the urine protein content. The results show a dissociation between the effects of estrogen on RNA or protein levels, which are decreased by thyroid hormones, and some early estrogenic responses (uterine edema and eosinophilia), which are decreased by thyroid hormones.