Effects of Hypophysectomy, Adrenalectomy, Cholesterol Feeding, and Puromycin on the Radiation-Induced Increase in Hepatic Cholesterol Biosynthesis in Rats

Abstract

The mechanism of the radiation-induced increase in hepatic cholesterol synthesis in rats, which we reported previously, has been further investigated by studies on (a) adrenalectomized, (b) hypophysectomized, (c) cholesterol-fed, and (d) puromycin-treated rats. Adrenalectomy greatly decreased the in vivo rate of synthesis of cholesterol, but did not prevent the enhancement due to irradiation. Hypophysectomy also reduced the in vivo synthesis to very low levels but in this case radiation failed to produce consistent or marked increases. Irradiation of cholesterol-fed rats increased the rate of cholesterol synthesis about 5-fold, measured either in vivo or in vitro. Esterified cholesterol levels in livers of cholesterol-fed rats were rapidly reduced by irradiation. Puromycin was used to obtain an estimate of the turnover rate of the enzymes necessary for cholesterol synthesis and also to determine if synthesis of protein is required for the appearance of the radiation-induced increase in cholesterol synthes...