Quantitative Variations in Serum Thyrotropin Levels During the Estrous Cycle of the Rat

Serum TSH levels have been quantitated during the various stages of the estrous cycle in female rats. Circulating thyrotropin was found to be higher during early estrus (42.2 ±6.8 mU100 ml; mean ±SE) than during any of the other stages (13.7–22.7 mU/100 ml), and there were no significant differences between these other stages. It is suggested that enhanced TSH secretion during early estrus is partially responsible for increases in thyroidal iodide accumulation previously demonstrated in late estrus. (Endocrinology 81: 121, 1967)