Lipolytic Activities in Rats Fed a Sucrose-Rich Diet Supplemented with either Cystine or Cholesterol: Relationships with Lipoprotein Profiles

Abstract

To study the relationships between lipolytic activities and plasma lipoprotein levels in rats, three diets were given for 8 weeks: a semipurifïed diet (based on sucrose, casein and lard) and this diet enriched with 5% cystine or with 1 % cholesterol. Both supplemented diets induced hypercholesterolemia. Lipoprotein analysis by density gradient ultracentrifugation of plasma indicated that hypercholesterolemia of cystine-fed rats (+52%) was characterized by an increased cholesterol level in high-density lipoprotein (HDL; +131 %) and low-density lipoprotein 2 (LDL₂; +147%), the lipoprotein fraction containing essentially apolipoprotein-E-rich high-density lipoproteins (HDLi), and was associated with a decreased cholesterol level in triglyceride-rich lipoproteins (TRL; -69%). That obtained by cholesterol feeding (+28%) was due to a large increase in the TRL cholesterol level (+315%) whereas cholesterol was reduced in HDL (-40%) and in LDL₂ (-60%). Under these dietary conditions, the activity of hepatic lipase (HL) was measured in liver homogenates and those of both HL and lipoprotein lipase were measured in plasma after heparin injection. The activity of HL (1,783 ± 132 mU/g liver in control rats) was increased by 48% in cystine-fed rats and decreased by 40% in cholesterol-fed rats. Similar changes were observed in the activity of both lipases measured in postheparin plasma. Highly significant positive correlations linked each lipolytic activity with the level of cholesterol, phospholipids and proteins in LDL₂ (HDL₁-rich fraction) and in HDL. In contrast, significant negative correlations were found between all of the TRL components and the activity of the lipases. These results suggest that the accumulation in plasma of HDL and of their final products of transformation in the rat, the HDL₁, is closely dependent on the intensity of the TRL lipolysis.