Effect of protein content and thyroid hormone on body composition in growing rats

Abstract

The effects of an isocaloric control diet of high-protein and low-protein diets (in which protein amounted to 16, 62 and 2% of total calorie content, respectively) with and without simultaneous administration of Thyreotom or methylthiouracil on total body composition have been studied in growing male Wistar rats. In spite of higher average Kcal intake (per day and 100 g of body weight), the rats on the high-protein diet were weighing less than the control animals at the end of the experiment. As compared to the control animals, the rats on the high-protein diet as well as those on the low-protein diet showed a greater relative weight of the thyroid gland. The protein percentage of the body was not significantly increased by an increase in protein supply; likewise, it was not significantly reduced by a decrease in protein supply. The body fat content was by 2/3 lower in the rats on the lowprotein diet than in the control animals. This difference was statistically significant. Thyroid hormones (1 mug liothyronine + 4 mug levothyroxine/100 g body weight, administered orally for 3 weeks) produced a slight increase of body protein in the rats on the high-protein diet; they increased it significantly in the rats on the low-protein diet. Body fat was correspondingly reduced. Methylthiouracil reduces the body fat content in the control animals and in the rats on the high-protein diet; it increased the body fat content in the rats on the low-protein diet. Our results confirm the partial findings of human pathology and demonstrate clearly that nutritional diseases, especially protein deficiency, worsen considerably in case of concomitant disorders of thyroid hormone metabolism.