Effect of thyroid hormone administration on estrogen-induced sex behavior in female mice.

Effects of thyroid hormones on reproductive processes have been described in sheep, birds, and rats. To extend this subject to mice for eventual analysis with genetically modified animals, we looked for effects of thyroid hormone treatment on lordosis behavior of ovariectomized estrogen-treated female mice. High doses of thyroid hormones reduced lordosis behavior. Since we could not explain this result by pharmacokinetic or peripheral effects, we infer that it worked by a central mechanism. Future investigations must determine whether endogenous fluctuations within the thyroid's normal physiological range have any behavioral effects.