A comparative study of hepatic HMG CoA reductase activity and LDL receptor relative mass in suckling and adult guinea pigs.

The reason why plasma cholesterol levels increase soon after birth is unknown but may be related to change rates of cholesterol synthesis and/or expression of LDL receptors. Plasma cholesterol levels, along with hepatic HMG CoA reductase activity, the rate-limiting enzyme of cholesterol synthesis, and hepatic LDL receptor relative mass were measured in suckling (1, 4 and 8 days of age) and adult guinea pigs. Plasma cholesterol was measured by an enzymatic assay, HMG CoA reductase activity was determined using a radiolabelled substrate and LDL receptor-relative mass was measured by ligand blotting with gold-labelled rabbit beta VLDL. Among the young animals, HMG CoA reductase activity and plasma cholesterol levels increased between 1 and 4 days of age. The LDL receptor mass did not change in the first 8 days after birth, but was 2-fold higher in adult than suckling animals. Hepatic HMG CoA reductase activity was also higher in the adult animals. Increased hepatic HMG CoA reductase and low LDL receptor mass may contribute to the elevation in plasma LDL cholesterol levels in the 4-day-old guinea pig.