Apoprotein C effect on triglyceride transport in tandem-perfused rat hind end and liver.

The metabolism of double-labeled triglyceride in a synthetic emulsion was defined in an in vitro perfusion system of rat hind end and liver described previously [Am. J. Physiol. 245 (Gastrointest. Liver Physiol. 8): G106-G112, 1983]. The metabolism of [3H]glycerol-[14C]triolein was defined in the absence of added apoproteins and with additions of human CII and both CII and CIII. Without apoprotein, a pronounced lipolysis of the triglyceride was recognized by high concentrations of radiolabeled glycerol and free fatty acid in the perfusate. The removal of an aliquot of hind-end venous effluent 5 min after adding the labeled triglyceride emulsion to the arterial inflow demonstrated a brisk lipolysis of the substrate when incubated outside the perfusion system. The addition of CII protein to the emulsion before its introduction into the tandem system eliminated perfusate lipolysis, both within the perfusion system and in incubations of aliquots withdrawn from the system. Intravascular lipolysis was not seen with triglyceride emulsions containing both CII and CIH or when an aliquot of hind-end venous effluent was incubated with triglycerides that had not been exposed to the perfusion system. The intravascular lipolysis observed for the [14C]triglyceride added to the tandem system without apoproteins was associated with relatively greater recoveries of 14C-fatty acyl in liver, fat, and muscle and relatively greater recoveries of 14CO2 than when CII alone or both CII and CIII were added with the triglyceride. The addition of CIII to CII in a 1:1 molar ratio increased the recovery of 14C-fatty acyl in muscle and the recovery as 14CO2.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterogeneity of human very low density lipoproteins by gel filtration chromatography.

Very low density lipoproteins were separated by gel filtration on Sepharose 4B. A decrease in mean particle diameter and flotation rate was seen with increasing elution volumes. The smaller lipoproteins had relatively more protein and phospholipid and less triglyceride than the larger ones. No differences were noted in the relative contents of the various phospholipids or partial glycerides between small and large lipoproteins. Fatty acid patterns of triglycerides and cholesteryl esters were also similar for the various lipoproteins. Relatively more lecithin containing linoleoyl acyl groups was found in smaller lipoproteins of some subjects. More of the protein of smaller lipoproteins was apo-LDL protein. Apo-HDL peptide was lost from the very low density lipoprotein as a consequence of the gel filtration.

Quantitation of the in vitro free cholesterol exchange of human red cells and lipoproteins.

The exchange of free cholesterol in vitro between human red blood cells and low density lipoproteins (LDL) was quantified. The flux of sterol between LDL and red cells was relatively constant over a wide range of concentrations of free cholesterol in lipoproteins. In a system containing a suspension of red blood cells in a mixed solution of high density lipoproteins (HDL) and LDL, the fractional rate of exchange of HDL cholesterol was most rapid followed by LDL and lastly, by red cells. Increasing the ionic strength of the incubation media had no effect on the exchange of cholesterol between LDL and red cells. However, when both HDL and LDL were incubated with red cells in a buffer of increased ionic strength, total red cell cholesterol exchange was unaltered, but proportionately more exchange occurred with HDL and less with LDL. Addition of acetone to the buffer increased the exchange of cholesterol between LDL and red cells but produced no increment in red cell-HDL exchange.