Studies on hepatic lipid metabolism in the oestrogenized male chick (Gallus domesticus)
The aim of this study was to investigate the early lipogenic events occurring in the liver after oestrogen treatment of the male chick in vivo. Liver weight increased with time after an injection of 17β-oestradiol (0•75 mg or 1 mg/100 g body wt.) to at least 40 hours. A dose-related increase in liver weight was observed 48 hours after an injection of 17β-oestradiol over the dose range 0 - 1•25 mg/100g body weight. Coincident with the increase in liver weight was a decrease in the DNA content and, in many cases, the soluble protein content of a unit weight of liver, substantiating the view that cell expansion, caused by accumulating water and lipid, contributes considerably to the liver enlargement after oestrogen treatment. Plasma triacylglycerol and phosphoprotein concentrations increased after an injection of 17β-oestradiol (1 mg/100 g body wt.), and became significantly greater than control values at 5 - 7½ and 14 - 18 hours post-injection, respectively. Liver slice lipogenesis was studied by measuring the incorporation of [1-(^14)C] acetate and (^3)H(_2)0 into total lipid, and of [9,10-(^3)H] palmitate into complex lipids. The incorporation of the radioisotope was predominantly into triacylglycerol in all cases. The livers of oestrogenized male chicks developed a significantly enhanced capacity to synthesize fatty acids de novo and to incorporate fatty acids into glycerolipids at times later than 14 hours after hormone injection. Results indicated that a stimulation of de novo lipogenesis at early times after injection (≤ 17 h) may be caused by handling and/or the injection of the vehicle propane-1,2-diol. Treatment of chicks with an optimum dose of 17β-oestradiol (0•75 mg/ 100 g body wt.) yielded results which suggested that early increases in hepatic fatty acid synthetase activity (≤ 26 h) are caused by handling and/or the injection of propane-1,2-diol, and that oestrogen-dependent changes occur within 48 hours.