Utilization of Exogenous Fat and Turnover Rate of Endogenous Fat in the Normal and Hypophysectomized Rat

¹ From the Department of Pediatrics, Western Reserve University School of Medicine, Cleveland, Ohio

The utilization of C¹⁴-labeled trilaurin and tripalmitin administered by both oral and intravenous routes and the turnover rate of total body fat was studied in normal and hypophysectomized rats. The hypophysectomized rats were found to utilize significantly more fat per millimole of CO₂ expired than normal rats. This increased utilization of exogenous fat varied from 14 to 97% for the various fats and routes of administration and was found in both fasting and fed rats. The turnover rate of endogenous total body fat was found to be almost twice as rapid in the hypophysectomized rats with the half-life of total body fat 9.0 ± 1.33 days as compared to 14.9 ± 0.15 days in the normal rats. The fat content of the hypophysectomized rats was 11.12 gm/100 gm body weight compared to 8.29 gm/100 gm body weight in the control rats. When both of these factors are taken into consideration, the hypophysectomized rats are found to utilize 0.86 ± 0.13 gm of endogenous fat/100 gm body weight/ day and the normal rats only 0.38 ± 0.04 gm of endogenous fat/100 gm body weight/day. In the presence of this marked increase in total fat metabolism in the hypophysectomized rats, there is only a slight hyperlipemia, which may be accounted for by an increased serum cholesterol, a decreased fat content of the liver and an increased total body fat.