The transfer of lipids that constitute the surface of lipoprotein particles, phospholipids and unesterified cholesterol, from chylomicrons and VLDL to other lipoproteins, mainly HDL, was examined. 2. Emulsions known to mimic the metabolism of chylomicrons labeled with [3H]-phosphatidylcholine, [14C]-cholesterol or [3H]-triolein were injected through a cannula implanted into the carotid artery of male Wistar rats weighing 280-350 g. Plasma clearance of the radioactively labeled emulsion lipid constituents and transfer of surface lipids from the emulsions to native HDL and LDL were measured in plasma samples collected at 2-min intervals during 10 min. 3. The transfer was measured in rats with alloxan-induced diabetes (single intraperitoneal dose, 140 mg/kg body weight) or with propylthiouracil-induced hypothyroidism (0.1% v/v in drinking water for 30 days), or given ethanol (20% in drinking water) for a period of 30 days, and in control rats. 4. The entry of emulsion phospholipids into the HDL fraction was not affected by the different treatments (controls: 9.3 +/- 0.6% of injected radioactivity, N = 8; diabetes: 12.5 +/- 2.4%, N = 9; hypothyroidism: 10.9 +/- 0.9%, N = 13; ethanol: 7.8 +/- 0.9%, N = 5). However, phospholipid transfer to the LDL fraction was increased in diabetes (10.0 +/- 2.3%) and hypothyroidism (12.1 +/- 1.3%) compared to controls (6.7 +/- 0.9%). Transfer of unesterified cholesterol from the emulsions to LDL and HDL was increased in both diabetic and hypothyroid rats (controls, LDL: 1.6 +/- 0.6%, HDL: 2.5 +/- 0.6, N = 5; diabetes, LDL: 5.3 +/- 1.2, HDL: 8.4 +/- 2.1 N = 5; hypothyroidism, LDL: 4.0 +/- 0.6, HDL: 3.6 +/- 0.4, N = 8). In ethanol-treated rats, transfer of surface lipids was similar to controls.
