Normal variation of plasma lipoproteins: postural effects on plasma concentrations of lipids, lipoproteins, and apolipoproteins.

We examined the effects of postural change on the concentrations of plasma cholesterol, triglyceride, high-density lipoprotein (HDL) cholesterol, apolipoproteins (apo) A-I and B, and lipoprotein(a) [Lp(a)] in six volunteers who fasted 12 h before blood sampling. Baseline samples were drawn in the standing position; the subjects then assumed the supine or sitting position, and additional blood samples were drawn at intervals up to 40 min. They then returned to the standing position and were again sampled at intervals up to 40 min. In the supine position, lipid, lipoprotein, and apolipoprotein concentrations decreased rapidly within the first 5 min and stabilized after 20 min. Total and HDL cholesterol, apoA-I, apoB, and Lp(a) decreased by as much as 7-12% in the supine position and returned to baseline values 20-40 min after the standing position was resumed. Smaller changes (5-9%) were observed when the subjects were sitting, and returned to baseline within 20 min after the subjects resumed the standing position. The decrease in triglycerides was 17% in the supine position and 10-11% in the sitting position. Lp(a) concentrations decreased 7-8% in either the supine or sitting position and returned to baseline more slowly than did the other components. For all components the changes were most rapid within the first 10 min after changing posture.