Increase of serum high density lipoprotein with progression and regression of aortic lipid deposition in rats.

The progression and regression of aortic lipid deposition was studied in male ExHC rats. Rats in the progression group were fed an atherogenic diet containing 2% cholesterol, 0.4% sodium cholate and 10% olive oil for periods up to 32 weeks. Rats in the regression group were first fed the atherogenic diet for 16 weeks, and then maintained on a basal low cholesterol diet. Half the rats were killed at 4 weeks and the other half at 16 weeks after cessation of the atherogenic diet. Rat aortas of the progression group contained progressively more lipid pari passu with the duration of cholesterol feeding, but connective-tissue proliferation was absent. Deposited lipid in the aorta of cholesterol-fed rats disappeared very slowly after the rats were returned to the basal diet. serum HDL decreased in the hypercholesterolemic ExHC rats fed the atherogenic diet for 4 weeks. By contrast, serum HDL and apo A-I increased in both hypercholesterolemic ExHC rats fed the atherogenic diet for 32 weeks and slightly hypercholesterolemic ExHC rats fed the basal diet for 16 weeks in the regression period.