Effects of insulin and acipimox on VLDL1 and VLDL2 apolipoprotein B production in normal subjects.

Author:

Malmström R1,Packard C J1,Caslake M1,Bedford D1,Stewart P1,Yki-Järvinen H1,Shepherd J1,Taskinen M R1

Affiliation:

1. Department of Medicine, University of Helsinki, Finland.

Abstract

The objective of the study was to examine the potential differential effect of insulin and acipimox (both of which reduce free fatty acid [FFA] availability) on VLDL apolipoprotein (apo) B metabolism. We studied eight healthy men (age 40 +/- 4 years, BMI 25.8 +/- 0.9 kg/m2, plasma triglycerides 1.30 +/- 0.12 mmol/l) after an overnight fast (control study, n = 8), during inhibition of lipolysis with an antilipolytic agent, acipimox (n = 8), and under 8.5-h euglycemic-hyperinsulinemic conditions (n = 5). Plasma FFAs were similarly suppressed in the acipimox and insulin studies (approximately 70% suppression). 2H3-leucine was used to trace apo B kinetics in VLDL1 and VLDL2 subclasses (Svedberg flotation rates: 60-400 and 20-60), and a non-steady-state multicompartmental model was used to derive the kinetic constants. The mean rate of VLDL1 apo B production was 708 +/- 106 mg/day at the beginning and 602 +/- 140 mg/day at the end of the control study. Production of the lipoprotein decreased to 248 +/- 93 mg/day during the insulin study (P < 0.05 vs. control study) and to 375 +/- 92 mg/day (NS) during the acipimox study. Mean VLDL2 apo B production was significantly increased during the acipimox study (399 +/- 42 vs. 236 +/- 27 mg/day, acipimox vs. control, P < 0.05) but not during the insulin study (332 +/- 51 mg/day, NS). The fractional catabolic rates of VLDL1 and VLDL2 apo B were similar in all three studies. We conclude that acute lowering of FFAs does not change the overall production rate of VLDL particles, but there is a shift toward production of smaller and denser VLDL2 particles, and, thus, the amount of total VLDL particles secreted remained constant. Insulin acutely suppresses the total production rate of VLDL apo B by decreasing the production of large triglyceride-rich VLDL1 particles. Based on these findings, we postulate that insulin has a direct suppressive effect on the production of VLDL apo B in the liver, independent of the availability of FFAs.

Publisher

American Diabetes Association

Subject

Endocrinology, Diabetes and Metabolism,Internal Medicine

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