Diurnal course of the suitability of serum samples obtained from normal subjects and from patients with primary endogenous hypertriglyceridaemia to serve as substrate for milk lipoprotein lipase

Abstract

Serum samples, obtained at various times of the day from four normal subjects and five patients with primary endogenous hypertriglyceridaemia on a carbohydrate-rich diet (meals at 09.00, 13.00 and 17.00 h), were incubated with cows' milk lipoprotein lipase (LPL) to investigate the susceptibility of the triglyceride(TG)-rich lipoprotein fraction to hydrolysis. Mean K_M and v_max of this reaction increased in patients between 09.00 and 13.00 h (p = 0.016 and 0.015, respectively) and decreased again thereafter, whereas no diurnal change was observed in normal subjects (p = 0.31 and 0.27, respectively). At 13.00 and 23.00 h patients showed a higher mean K_M (p<0.02) at at 23.00 h a higher mean v_max (p<0.03) than normal subjects. When the data were expressed as reaction rates (FFA formation rates) at TG-concentrations in the in vivo range, neither group showed a diurnal difference. Patients showed a significantly lower reaction rate than normal subjects only at 13.00 h at TG concentrations below 3 mmol·1^-1. This suggests that a defect in the suitability of TG-rich particles to serve as a substrate for LPL is not likely to play a role in the development of hypertriglyceridaemia.

Key Words:

• apolipoproteins
• chylomicrons
• hyperlipoproteinaemia type IV
• lipolysis
• lipoproteins
• VLDL
• triglycerides