Differences in growth and thyroid activity persisting in adult rats reared in nests of different sizes during...

The undernutrition or overnutrition during a suckling period achieved by adjusting the number of infants per lactating rat to 4 (overfed-0), 8 (control-C) or 14 (underfed-U) resulted in long lasting differences in body weight. The consumption of the diet in 260-day old males and females was similar in all experimental groups if expressed per unit of body weight, thus suggesting the differences in energy utilization. An increase of thyroid hormone secretion rate was found in U rats aged 30, 120 and 300 days as compared to 0 ones. Serum TSH level was also higher in U rats at the age of 30 days and 1 year. However, serum thyroxine level in U groups was either higher or similar as in controls. Paper chromatography of thyroglobulin hydrolyzate 24 h after 125I injection to 300 days old males showed a decrease of radioactivity in iodide area in U animals and an increase in triiodothyronine area in 0 animals. The analysis of thyroglobulin from 200 days old females on linear sucrose gradient did not reveal any rough change in its iodination. The results indicate an increase of thyroid activity in adult, previously moderately underfed male and female rats. Some changes in feedback sensitivity of hypothalamo-pituitary-thyroid axis may presumably also occur in these animals.