Effect of serum lipoproteins of bile obstructed rats on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in perfused rat liver.

Total lipoproteins as well as fractionated VLDL + LDL and HDL from fasted control rats and bile-ligated rats were tested in liver perfusion for their effect on 3-hydroxy-3-methylglutaryl CoA reductase activity in normal rat livers. The total lipoproteins of bile-obstructed rats had 3 times greater capacity to increase 3-hydroxy-3-methylglutaryl CoA reductase activity than that of the control total lipoproteins. When the fractionated lipoproteins were tested from fasted control rats, it was found that the major stimulating activity was in the HDL fraction with minor activity in the VLDL + LDL fraction. When these plasma components isolated from fasted bile-ligated rats were tested, it was found that the major activity had shifted to the VLDL + LDL fraction with the HDL having only a minor stimulatory role. The possible mechanism of action of the abnormal lipoproteins associated with bile obstruction in regulating 3-hydroxy-3-methylglutaryl CoA reductase activity is discussed.