Diurnal changes in serum triglycerides as related to changes in lipolytic enzymes, (apo) lipoproteins and hormones in normal subjects on a carbohydrate-rich diet.
Normal subjects in steady state on a carbohydrate-rich diet (three equivalent meals a day at 9.00, 13.00 and 17.00 h), show a wave-like serum triglyceride (TG) pattern with a peak at 14.00 h. Post-heparin lipoprotein lipase (LPL) activity increased from a mean value of 49 mU/ml +/- 13 (SD) in the fasting state to 127 mU/ml +/- 18 in the fed state (P less than 0.005). This was due to an increase in adipose tissue LPL activity which, at 16.30 and 21.30 h, was significantly higher than basal levels (128.3 +/- 81.5 and 87.7 +/- 23.2 v. 43.3 +/- 9.3 mU/g, P less than 0.05 and P less than 0.01, respectively). Skeletal muscle LPL activity was low (5.8 mU/g +/- 2.3, mean +/- SD) and showed no diurnal change. The observed changes in TG-hydrolysing capacity in the course of the day might explain the TG-pattern. High density lipoprotein (HDL) subfractions HDL2 and HDL3 were separated by density gradient ultracentrifugation and had mean hydrated densities of 1.088 and 1.135 g/ml, respectively. While HDL2 showed no diurnal change, HDL3-cholesterol and-phospholipid significantly increased during the day (P less than 0.005 and P less than 0.001 respectively), reaching their highest levels in the evening. Since te rise in HDL3-lipids follows the fall in serum TG, this provides further indication that the metabolism of these fractions in mutually related.
D000273:Adipose Tissue / Q000201:enzymology; D000328:Adult; D001059:Apoproteins / Q000097:blood; D002940:Circadian Rhythm / Q000187:drug effects*; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D005934:Glucagon / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008074:Lipoproteins / Q000097:blood*; D008075:Lipoproteins, HDL / Q000097:blood; D008297:Male; D014280:Triglycerides / Q000097:blood*
D001059:Apoproteins; D004040:Dietary Carbohydrates; D007328:Insulin; D008074:Lipoproteins; D008075:Lipoproteins, HDL; D014280:Triglycerides; D005934:Glucagon; D008071:Lipoprotein Lipase