Abstract
The effects of dietary lipid and daily food-uptake on hepatic HMG-CoA reductase (β-hydroxy-β-methylglutaryl CoA reductase) activity and serum cholesterol level of the normal and diabetic rats were studied.
The animals were maintained ad lib on either carbohydrate diet (dextrose 75%, casein 20% and vitamins et salts 5%) or fat diet (dextrose 30%, casein 20%, vitamins et salts 5%, corn oil 20% and indigestible fibres 25%) for five days from 8 o'clock in the morning till 6 o'clock in the evening. Daily food consumption per animal under these conditions were nearly 60 calorie and no significant differences were observed. The other groups of normal and diabetic animals forcedly fed one of the two kinds of the diet 76 calories daily for four days, were also studied. The measurements of the enzyme activity were done at noon and midnight. The serum samples were obtained at noon and used for cholesterol analysis.
The diurnal variations of the enzyme activity were shown on the all groups observed. The lipid feeding markedly stimulated the HMG-CoA reductase activity of both normal and diabetic rats. Increased consumption of the diets also stimulated the enzyme activity in most of normal and diabetic animals. However, these stimulatory effects on the reductase activities by the different dietary states were neither accompanied by increase nor decrease of serum cholesterol level.
These discrepancies between the hepatic cholesterogenesis and serum cholesterol level suggest that the liver has rather limited contribution to the whole cholesterogenesis or that the breakdown of serum cholesterol is also stimulated coordinately with it's hepatic production by these dietary manipulations. The possible mechanisms of the diurnal variations of the activity and the indUction of hepatic HMG-CoA reductase by dietary lipid or increased food uptake were discussed.
