Journal of Lipid Research, Vol. 18, 465-473, July 1977
Copyright © 1977 by Lipid Research, Inc.

Secretion of the arginine-rich and A-I apolipoproteins by the isolated perfused rat liver

Tünde E. Felker , Menahem Fainaru , Robert L. Hamilton , and Richard J. Havel

Cardiovascular Research Institute and Departments of Anatomy and Medicine, University of California, San Francisco, CA 94143

Rates of secretion of the arginine-rich and A-I apolipoproteins into perfusates of rat livers were measured by specific radioimmunoassays. Livers were perfused for 6 hr in a recirculating system in the presence or absence of 5,5'-dithionitrobenzoic acid, an inhibitor of lecithin-cholesterol acyltransferase. Arginine-rich apoprotein (ARP) was secreted at a constant or increasing hourly rate of about 40 µg/g liver, whereas the rate of accumulation of apoprotein A-I decreased progressively from about 12 to less than 5 µg/g liver. These rates were not affected by inhibition of lecithin-cholesterol acyltransferase. The distribution of these two apolipoproteins was also measured in ultracentrifugally separated lipoprotein fractions from perfusates and blood plasma. Apoprotein A-I was mainly in high density lipoproteins, with the remainder in proteins of density > 1.21 g/ml. The percent of apoprotein A-I in the latter fraction was lowest in plasma (5%); in perfusates it was greater when the enzyme inhibitor was present (33%) than in its absence (11%). By contrast much less ARP was in proteins of d > 1.21 g/ml in perfusates than in blood plasma. Discoidal high density lipoproteins, recovered from perfusates in which lecithin-cholesterol acyltransferase was inhibited, contained much more arginine-rich apoprotein than apoprotein A-I (ratio = 10:1). The ratio in spherical plasma HDL was 1:7 and that in perfusate high density lipoproteins obtained in the absence of enzyme inhibitor was intermediate (2:1). It is concluded that: 1) the arginine-rich apoprotein is a major apolipoprotein whereas apoprotein A-I is a minor apolipoprotein secreted by the perfused rat liver; 2) the properties of the high density lipoproteins produced in this system are remarkably similar to those found in humans with genetically determined deficiency of lecithin-cholesterol acyltransferase.

Supplementary key words radioimmunoassay • lipoproteins • lecithin-cholesterol acyltransferase • SDS gel electrophoresis • isoelectric focusing

Submitted on October 12, 1976
Accepted on February 25, 1977

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