NON-STEADY-STATE KINETICS OF LOW-DENSITY LIPOPROTEINS IN MAN - STUDIES AFTER PLASMA-EXCHANGE IN HEALTHY-SUBJECTS AND PATIENTS WITH FAMILIALHYPERCHOLESTEROLEMIA

Five patients with heterozygous familial hypercholesterolaemia (FH), o ne patient with non-familial hypercholesterolaemia, and four healthy n ormals were treated with plasma exchange (PE). In order to achieve a n on-steady-state situation with low plasma cholesterol levels, PE was p erformed twice in each subject at an interval of 1-3 days. At each tim e, 1500 ml of plasma were removed and replaced with colloids and album in. Lipoprotein analyses were performed daily in all subjects for a pe riod of 14 days following PE. Kinetic calculation of LDL cholesterol d ata using a two-compartment open model was performed, and rate constan ts, synthetic rate and apparent clearance of LDL were determined. A lo wer clearance and a tendency towards a higher synthesis of LDL were ob served in the FH patients. In four of the subjects, LDL kinetics was a lso studied with the conventional I-125-LDL turnover technique. The sy nthetic rates of LDL were compared using data derived from PE and I-12 5-LDL kinetics. The two techniques showed a good correlation (r = +0.9 3) although synthetic rates in general were higher when calculated fro m the I-125-LDL procedure (3.98 vs. 2.64 mmol d(-1) for LDL cholestero l synthesis). The results indicate that non-steady-state kinetics of L DL, as measured using the PE technique, is a useful method for analysi s of LDL metabolism.