Secretion of lipoprotein-X by perfused livers of rats with cholestasis.

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Abstract
The major abnormal plasma lipoprotein of cholestasis (LP-X) was isolated from blood plasma and from perfusates of isolated livers of rats with biliary obstruction. In both cases LP-X was composed mainly of approximately equimolar parts of phospholipids and unesterified cholesterol. The small protein component was primarily the arginine-rich apolipoprotein. By EM, LP-X appeared as a unilamellar liposome (690 .ANG. mean diameter, range 400-1000 .ANG.) with the trilaminar staining image typical of phospholipid bilayers. Extensive block staining of cholestatic livers of 48 h with warmed uranyl acetate (37.degree.) permitted the visualization of vesicles indistinguishable from LP-X within hepatic parenchyma. These trilaminar-staining vesicles occurred predominantly within bile canaliculi. They also were seen in nearby cytoplasmic vacuoles or invaginations between hepatocytes and in the space of Disse. Similar vesicles were not seen in the endoplasmic reticulum or Golgi cisternae. The vesicles may be formed within bile canaliculi and transported from the canaliculi to the space of Disse within pinocytotic vacuoles.