Effects of short-term melatonin administration on lipoprotein metabolism in normolipidemic postmenopausal women

Abstract

Objective: To investigate the effects of short-term administration of melatonin on lipoprotein metabolism in normolipidemic postmenopausal women. Methods: Fifteen such women received 6.0 mg melatonin daily for 2 weeks. Blood was sampled before and after treatment. We measured concentrations of total cholesterol and total triglyceride in the plasma, as well as the levels of cholesterol, triglyceride, and protein in the very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL). Plasma apolipoprotein levels were determined by immunoturbidimetric assay. Activities of lipoprotein lipase, hepatic triglyceride lipase, and lecithin cholesterol acyltransferase were also determined by enzymatic analysis. Results: Melatonin administration significantly increased the plasma levels of triglyceride by 27.2% ( P<0.05), of VLDL-cholesterol by 37.2% ( P<0.01), of VLDL-triglyceride by 62.2% ( P<0.001), and of VLDL-protein by 30.0% ( P<0.05). However, the plasma total cholesterol level and the concentration of lipid and protein in LDL and HDL were not significantly affected. Melatonin significantly increased the plasma levels of apolipoprotein C-II by 29.5% ( P<0.005), of C-III by 17.1% ( P<0.001), and of E by 7.6% ( P<0.05). The plasma levels of apolipoprotein A-I, A-II, and B were not altered. Melatonin significantly inhibited the activity of lipoprotein lipase by −14.1% ( P<0.05), but did not significantly affect the activities of hepatic triglyceride lipase or of lecithin cholesterol acyltransferase. Conclusions: Findings indicate that melatonin increases the plasma level of VLDL particles by inhibiting the activity of lipoprotein lipase, but may not affect the plasma levels of LDL and HDL particles in postmenopausal women with normolipidemia.