Effect of Hyperthyroidism on Body Weight Gain and Feed Consumption in Male and Female Rats.

Summary Male and female rats of Sprague-Dawley-Rolfsmeyer strain, age 26 days, were injected daily with 3.0, 6.0, 9.0, and 12.0 μg L, thyroxine/100 g BW for 200 days in comparison with normal groups. Lowest level was 3 X mean TSR and equal to highest rate observed in lactating rats. In females, weight gain was reduced by less than 10% in comparison with controls with increasing age, and no trend toward greater weight restriction was observed on higher levels of T4. In males, increased weight restriction appeared at 40 days and beyond, and was more marked than in females. Levels of 6 μg and above permitted gain equal to 60 to 70% of that of controls. Food consumption increased progressively on higher T4 levels but females showed less increase than did males.