Differences among Hyperlipoproteinaemic Subjects in the Response of Lipoprotein Lipids to Resin Therapy

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Abstract
Ih has been reported that cholesterol turnover is raised when hypercholesterolaemia occurs in association with elevated levels of very low density lipoprotein, but normal when hypercholesterolaemia reflects an increase in the concentration of low density lipoprotein alone. The relationship of plasma lipoprotein levels to cholesterol metabolism has been further investigated in the present experiments, in which the acute effects on lipoprotein lipids of stimulating cholesterol turnover with a bile acid-sequestering resin, colestipol, have been compared in normal subjects and in patientw with four types of hyperlipoproteinaemia. Very low density lipoprotein (VLDL) lipids increased in every subject. The increase was greatest in patients with type IV or type V hyperlipoproteinaemia, least in normal subjects and in those with type IIa hyperlipoproteinaemia, and intermediate in patients with type IIb hyperlipoproteinaemia. The induced increments in VLDL cholesterol and triglyceride mass were accordingly positively correlated with the pre-treatment concentrations. Low density lipoprotein (LDL) lipids decreased during resin therapy in all subjects, except those with type IV or type V hyperlipoproteinaemia in whom there was a transient rise. The reductions in LDL cholesterol were significantly greater in patients with type II hyperlipoproteinaemia than in the normal volunteers, and in both groups of subjects were proportionately greater than those in LDL triglyceride. These findings demonstrated clear differences among the hyperlipoproteinaemias in the response of lipoprotein lipids to resin therapy, and profide further evidence for the heterogeneity of cholesterol metabolism in these conditions. The colestipol-induced changes in type UV and type V patients could be partially reproduced in normal subjects during the consumption of high carbohydrate diets, which might be expected to increase VLDL synthesis. It is suggested, therefore, that the synthesis of VLDL cholesterol may be enhanced in such patients, and that any rise in LDL cholesterol observed during resin therapy reflected subsequent metabolism of VLDL to LDL rather than diminished LDL cholesterol clearance.