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 7500 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 µmol 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 8.1±1.6 µmol
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.
