On the metabolism of lipoprotein-X (LP-X)

The characteristic low-density lipoprotein of cholestasis (LP-X) earlier described for humans is found with identical properties in dogs and rats after experimental cholestasis. After ligation of the common bile duct, LP-X may be detected in the plasma within the first 20 hours. A period of marked increase in concentration is followed by decreasing plasma concentrations and LP-X becomes undetectable 7-10 days after ligation of the bile duct in rats. High plasma bile salt concentration may alter the structural integrity of LP-X and may in part be responsible for its disappearance after long-lasting and severe biliary obstruction. Plasma decay curves for isolated LP-X injected intravenously into healthy animals revealed a rapid early fall in concentration followed by a gradual decline. The calculated fractional catabolic rate of LP-X was found to be 0.450 +/- 0.069 for dogs and 1.553 +/- 0.096 for rats corresponding to a mean biological half life of 37.7 +/- 6.4 h or 10.7 +/- 0.6 h, respectively. In vitro LP-X degradation occurs in post-heparin plasma, however, it seems to be too early to speculate on the enzyme activity and on the mode of action responsible for this disappearance.