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Effect of dietary cholesterol and cholestyramine on developmental pattern of 3-hydroxy-3-methylglutaryl-CoA reductase
Insights
Dietary cholesterol and cholestyramine impact liver and intestinal reductase activity in chicks. Cholesterol increased membrane cholesterol, suggesting a role in regulating enzyme activity during early development.
Area of Science:
- Biochemistry
- Developmental Biology
- Nutritional Science
Background:
- Cholesterol metabolism regulation is crucial for cellular function.
- 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) is a key enzyme in cholesterol synthesis.
- Understanding early-life regulation of cholesterol metabolism is important.
Purpose of the Study:
- To investigate the effects of dietary cholesterol and cholestyramine on HMGCR activity and membrane composition in neonatal chicks.
- To explore the relationship between HMGCR activity and membrane lipid alterations.
Main Methods:
- Chicks were fed diets supplemented with cholesterol or cholestyramine.
- Hepatic, intestinal, and brain HMGCR activity was measured.
- Cholesterol and lipid phosphorus levels in microsomal membranes were analyzed.
Main Results:
- Dietary cholesterol suppressed the normal increase in hepatic and intestinal HMGCR activity post-hatching.
- Cholestyramine increased hepatic and intestinal HMGCR activity.
- Brain HMGCR activity remained unchanged by either dietary intervention.
- Dietary cholesterol increased the cholesterol/lipid phosphorus ratio in hepatic and intestinal membranes.
- Cholestyramine did not alter this ratio in postnatal development.
Conclusions:
- Dietary cholesterol and cholestyramine differentially regulate HMGCR activity in chick liver and intestine.
- Changes in membrane cholesterol/lipid phosphorus ratio, indicative of altered membrane fluidity, may mediate HMGCR regulation in hepatic and intestinal tissues.
- This regulatory mechanism appears to be active during the neonatal period.
Abstract:
Supplementation of the diet with 2% cholesterol suppressed the increase observed in the hepatic and intestinal 3-hydroxy-3-methylglutaryl-CoA reductase activity from normally fed chicks during the first days after hatching. Cholestyramine feeding clearly increased both hepatic and intestinal reductase activities. In contrast, brain reductase did not show significant changes by cholesterol or cholestyramine feeding. Dietary cholesterol produced a clear increase in the cholesterol/lipidic phosphorus molar ratio of hepatic and intestinal microsomal membranes. However, this molar ratio did not change by cholestyramine feeding during postnatal development. Both dietary cholesterol and cholestyramine had practically no effect on the cholesterol/lipidic phosphorus molar ratio of brain microsomes. The relationship between the inhibition of reductase activity by dietary cholesterol and the increase of cholesterol/lipidic phosphorus molar ratio is in agreement with a mechanism of regulation of both hepatic and intestinal reductase by alterations of membrane fluidity, mechanism that would be already operative during the neonatal period.