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Effect of Estrogen and Progesterone on Thyroid Function of Cattle^{1, 2,}

Department of Dairy Husbandry, University of Missouri, Columbia

ABSTRACT

A preliminary study is presented concerning the possible role of the ovarian hormones (estrogen and progesterone) upon the rate of secretion of thyroid hormone during estrus and pregnancy. For this purpose, a technique was developed consisting of the measurement of thyroidal-I¹³¹ release when recycling of I¹³¹ was prevented by a goitrogen (thiouracil) during a preliminary control period. During the subsequent period of ovarian hormone injection, the measurement of release rate is continued. If a change in release rate is noted, it is believed to indicate that a change in thyroxine secretion rate has been induced. The injection of 100 mg. per day of progesterone alone or in combination with 100 µg. of estradiol benzoate failed to alter the release rate of thyroidal I¹³¹ in groups of dairy cattle. While 1.15 mg. estradiol benzoate alone also failed, when 2.5 or 3.0 mg. were injected daily, the release rate was increased to a statistically significant extent. These observations are interpreted as indicating that the level of estrogen secreted in late pregnancy stimulates increased secretion of thyrotropin and thyroxine during early lactation.

¹ Contribution of the Missouri Agricultural Experiment Station, Journal Series No. 1871. Approved by the Director.

² Aided in part by a grant from the U. S. Atomic Energy Commission, Contract No. AT(11-1)-301.