EFFECT OF LEVEL OF THYROID ACTIVITY ON RESPONSE OF OVARIECTOMIZED RATS TO ESTRONE

Abstract

Daily admn. of dl-thyroxin by subcutaneous injn. at levels of 1, 2, and 3 7/g. of body wt. for 3, 6 and 10 days decreased estrus response of ovariectomized rats to 1.5 7 of estrone detd. by the method of vaginal smears. Weight loss and decrease in sensitivity to estrone appeared to be logarithmic functions of thyroxin dosage. Twenty-eight days after a 10-day period of thyroxin, dosage response to estrone returned to normal. Thyroparathyroidectomy resulted in an increase in estrus response of ovariectomized rats to 1.3 y of estrone. Response of a group of 50 operated animals was 76% above that of the controls 38 days after operation. Increased sensitivity was partially corrected by 3 daily injns. of 0.1 7 of thyroxin/g. of body wt. The daily admn. of thiourea at levels of 0.05, 0.1, and 0.3% in drinking water of ovariectomized rats over a period of 70 days inhibited growth and produced marked hyperemia and enlargement of the thyroid gland. Estrus response of spayed rats to 1.3 7 of estrone was first reduced and then increased as dosage with thiourea continued. After 42 days of dosage, the response to estrone approached that surgically thyroparathyroidectomized rats. The rat unit of estrone was detd. at 3 different levels of thyroid function. The unit as detd. on a normal ovariectomized colony was 1.33 [gamma]. On a thyroparathyroidec-tomized colony it was 0.86 [gamma], and when detd. on a colony rendered hyperthyroid by 6 daily injns. of 2 7 of thyroxin/g. of body wt. the unit was 2.50 [gamma].