Biology of Reproduction, Vol 11, 529-533, Copyright © 1974 by Society for the Study of Reproduction

Rat Ovarian and Uterine Response to Gonadotropin as Modifled by Triiodothyronine

¹ Department of Obstetrics and Gynecology, University of Maryland, Baltimore, Maryland 21201

The effect of triiodothyronine (T₃) on the ovarian and uterine response to pregnant mare's serum gonadotropin (PMSG) was studied. Following PMSG (10 IU x 3 days), tubal ova were found consistently on Day 4. The mean number of ova was 24 ± 3. Pretreatment with 1, 5, or 10 µg T₃ or the ethanol—saline vehicle did not prevent ovulation; however, the number of ova found was less with 5 or 10 µg T₃ (14 ± 2 and 15 ± 3, respectively). Serum progesterone was increased from 2.5 ± 0.9 to 17.9 ± 3.0 ng/ml following PMSG treatment. Pretreating with T₃ did not affect serum progesterone levels. The increased uterine weight following PMSC was not affected by T₃, but a large proportion of uteri were ballooned in T₃ pretreated rats, despite normal serum progesterone. It appears that T₃ interferes with the action of progesterone at the level of the uterus.