Body composition and in vitro lipid metabolism of overfed hypophysectomized rats

Hypophysectomized (hypox) rats were fed ad libitum or were tube-fed increasing levels of their normal food intake. Sham operated (sham) rats were tube-fed to maintain their normal rate of growth or were fed 150 percent of their ad libitum food intake. This was equivalent to the highest intake of hypox rats. Overfeeding continued for 20 days. Overfeeding hypox rats increased body weight almost entirely by hypertrophy and hyperplasia of body fat depots. Overfeeding did not promote growth of lean tissue in hypox rats. Serum insulin increased with higher levels of food intake and extreme overfeeding resulted in hyperinsulinemia and hyperglycemia in hypox rats. Serum thyroid hormones and corticosterone were lower in hypox than sham rats and were not significantly changed by overfeeding. Adipose and hepatic fatty acid synthesis and esterification and adipose glycerol release were measured in vitro. Although serum insulin increased, peripheral tissue of overfed hypox rats remained insulin resistant. Rates of hepatic and adipose lipid synthesis and adipose lipolysis appeared to be determined by nutrient availability rather than being dependent upon pituitary factors.