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

Objective: To investigate the effects of short-term administration of melat onin on lipoprotein metabolism in normolipidemic postmenopausal women. Meth ods : Fifteen such women received 6.0 mg melatonin daily for 2 weeks. Blood was sampled before and after treatment. We measured concentrations of tota l cholesterol and total triglyceride in the plasma, as well as the levels o f cholesterol, triglyceride. and protein in the ver); low-density lipoprote in (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL ). Plasma apolipoprotein levels were determined by immunoturbidimetric assa y. Activities of lipoprotein lipase, hepatic triglyceride lipase, and lecit hin cholesterol acyltransferase were also determined by enzymatic analysis. Results: Melatonin administration significantly increased the plasma level s 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 concentra tion of lipid and protein in LDL and HDL were not significantly affected. M elatonin significantly increased the plasma levels of apolipoprotein C-II b y 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 hepat ic triglyceride lipase or of lecithin cholesterol acyltransferase. Conclusi ons: Findings indicate that melatonin increases the plasma level of VLDL pa rticles by inhibiting the activity; of lipoprotein lipase, but may not affe ct the plasma levels of LDL and HDL particles in postmenopausal women with normolipidemia. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.