Effect of type of diet and feeding status on modulation of hepatic HMG‐CoA reductase in rats

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Abstract
The effect of diet type and feeding status on hepatic HMG‐CoA reductase (HMGR) [mevalonate: NADP+ oxidoreductase (acylating CoA); EC 1.1.1.34] was studied in rats. Animals fed a ground, commercial, stock diet exhibited higher expressed and total activities of HMGR in the fed state than animals fed a semi‐purified diet. The differences did not appear in meal‐trained animals when measured before the onset of the meal after a 22‐hr fast. When expressed activity was taken as a per cent of total activity, fed animals from both diet groups used about 10% of their available activity. When animals on commercial diets were fasted, 20% of the activity was expressed. Fasted animals on the semi‐purified diet also increased the per cent of expressed reductase activity, but this increase was not as great (13.3%). These data suggest that, in the rat, regulation of cholesterol synthesis in response to decreased total HMGR during fasting and increased levels after a meal results from alterations in the percentage of enzyme which is expressed. The semi‐purified diet used here resulted in consistently lower levels of HMG‐CoA reductase activity than the commercial diet regardless of feeding pattern.