Preliminary report increased transport of intermediate density lipoprotein (LDL) with cholesterol loading

Although cholesterol loading in man generally leads to an increase in plasma cholesterol and low density lipoprotein cholesterol in particular, the mechanism for this is unknown. Because IDL formation rises in cholesterol-fed rats we have measured the transport of IDL apoprotein B in 8 men during two dietary periods containing either 200 mg or 1700 mg cholesterol per day. Radioiodinated IDL (Sf 12-20 or Sf 12-60) were reinjected and transport calculated from 48 hr specific radioactivity-time curves of apoprotein B in reisolated IDL. With cholesterol loading the IDL cholesterol and apoprotein B concentrations rose in 7 of 8 subjects (substantially in only 2). However IDL transport was stimulated more consistently and significantly (p less than 0.01), rising by at least 50% in 5 subjects. Furthermore the change in plasma total cholesterol concentration was significantly correlated with the change in IDL transport (r = +0.70, p less than 0.05). Since LDL are derived from IDL, the cholesterol-induced rise in IDL formation may explain the increase in LDL concentration with dietary cholesterol.