A COMPARATIVE-STUDY OF HEPATIC HMG COA REDUCTASE-ACTIVITY AND LDL RECEPTOR RELATIVE MASS IN SUCKLING AND ADULT GUINEA RIGS

The reason why plasma cholesterol levels increase soon after birth is unknown but may be related to change rates of cholesterol synthesis an d/or expression of LDL receptors. Plasma cholesterol levels, along wit h hepatic HMG CoA reductase activity, the rate-limiting enzyme of chol esterol synthesis, and hepatic LDL receptor relative mass were measure d in suckling (1, 4 and 8 days of age) and adult guinea pigs. Plasma c holesterol was measured by an enzymatic assay, HMG CoA reductase activ ity was determined using a radiolabelIed substrate and LDL receptor-re lative mass was measured by ligand blotting with gold-labelled rabbit beta VLDL. Among the young animals, HMG CoA reductase activity and pla sma 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 reductas e activity was also higher in the adult animals. Increased hepatic HMG CoA reductase and low LDL receptor mass may contribute to the elevati on in plasma LDL cholesterol levels in the 4-day-old guinea pig.