Journal of Lipid Research, Vol 24, 156-166, Copyright © 1983 by Lipid Research, Inc.
Metabolism of two forms of apolipoprotein B of VLDL by rat liver
CE Sparks, DJ Rader and JB Marsh
Apolipoprotein B (apoB) is composed of metabolically distinct fractions of
higher molecular weight (apoBh) and lower molecular weight (apoBl). When
125I-labeled very low density lipoprotein (VLDL) prepared from
recirculating liver perfusates was injected into rats, labeled apoBl was
preferentially removed from the plasma and apoBh entered low density
lipoprotein (LDL). The time-related movement of labeled apoBh into higher
density fractions was independent of that of labeled apoBl. When
125I-labeled triglyceride-rich lipoprotein (TRL) prepared from sucrose-fed
rats was incubated with plasma from rats injected with heparin and then
studied in a recirculating liver perfusion, apoBl was preferentially
removed compared to apoBh. Thus, the loss of apoBl of hepatic VLDL in vivo
was similar to the loss of apoBl of lipase-treated TRL in vitro. In control
perfusions where TRL was incubated with heat- treated postheparin plasma,
not only was there less initial hepatic clearance of apoB but the early
phase of preferential apoBl removal during 30 min of perfusion was not
observed. ApoE removal from perfusates was the same whether or not the TRL
had been treated with heparin-releasable lipases. Apoprotein degradation,
as indicated by the appearance in the perfusate of labeled degradation
products, occurred 30 min after the preferential phase of apoBl removal.
These results suggest that hepatic clearance of VLDL and TRL remnants is
favored by lipolysis and by the presence of apoBl on the particle that
enhances their hepatic binding and degradation.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
