Abstract
The growth of fetuses of 50% calorie-restricted (R) rats was retarded by approximately 1 day as compared with that of ad libitum fed control (C) rats. Nevertheless, the thyroid glands in such growth-retarded fetuses developed in proportion to the size of fetuses, as did the thyroid follicular cell height and the follicular diameter. Pregnant rats were treated with 40 mg propylthiouracil (PTU) each day for 2 days and autopsied on the third day in various gestational periods of Days 17-19, 18-20, 19-21, and 20-22. PTU given to C rats on Days 17 and 18 of gestation did not alter the fetal thyroid weight and histology on Day 19. When given on Days 18 and 19, or later, PTU caused a significant increase in the thyroid weight and follicular cell height. However, when given to R rats on Days 18 and 19, PTU did not influence the fetal thyroid. When given on Days 19 and 20, or later, PTU was effective in R rats. Thus, in fetuses of the R rats, the reciprocal relationship between the pituitary and the thyroid appears to be established with a 1-day delay as compared with the C rats, similar to the 1-day retardation in body weight gain.
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