The influence of early postnatal overnutrition on peripheric thyroxine metabolism in rats

The influence of postnatal overnutrition on thyroid metabolism in later life was studied in male rats reared in small nests (2 pups per dam). At an age of 3 months postnatally overfed rats differ from normally bred rats (12 pups per dam) by a significant higher thyroxine and lower triiodothyronine concentration in plasma. Kinetic data of thyroxine metabolism point out a lower fractional turnover rate and a lower metabolic clearance rate per 100 g body mass corresponding with a reduced 131I-uptake by the thyroid gland. A lower energy intake per metabolic mass unit and a lower energy need for maintenance in postnatally overfed rats calculated from intake and body mass development are discussed in respect of correlations between changes of thyroid hormone metabolism and efficiency of energy utilization.