Background: We investigated whether variations in lipoprotein lipase activity, a key post-prandial enzyme involved in the removal of circulating dietary triglycerides, could contribute to the previously described nocturnal lipid intolerance.
Methods: We studied lipoprotein lipase activity in 12 healthy volunteers (five women, seven men) at 11:30 h and 23:30 h on two separate occasions. Subjects consumed a high-fat mixed meal at 07:30 h for the morning study or 19:30 h for the evening study. Then, after a 4-h fast, subjects were given an intravenous bolus of 7,500 U heparin. Blood samples were collected before and 15 min after heparin administration for measurement of lipoprotein lipase, hepatic lipase, triglycerides and non-esterified fatty acids concentrations.
Results: Post-prandial post-heparin lipoprotein lipase activity was greater in the morning than in the evening (16.5 +/- 1.4 versus 14.4 +/- 1.0 micromol oleate/mL/h; P< 0.05). Post-prandial post-heparin hepatic lipase activity was also greater in the morning than in the evening (8.7 +/- 1.5 versus 81 +/- 1.6 micromol oleate/mL/h; P= 0.002). There were no other significant diurnal differences.
Conclusion: We report a diurnal variation in post-prandial lipoprotein lipase activity. This is consistent with the notion that decreased nocturnal insulin sensitivity extends to insulin's actions on lipoprotein lipase and provides a possible explanation for nocturnal lipid intolerance.