Competition between chylomicrons and their remnants for plasma removal: a study with artificial emulsion models of chylomicrons.
In previous studies, protein-free emulsions of defined lipid composition were shown capable of simulating either the metabolism of chylomicrons (chylomicron-like emulsion) or their remnants (remnant-like emulsion), depending on the content of free, unesterified cholesterol. To validate further the assumption that remnant-like and chylomicron-like emulsion have metabolic pathways in common with their natural counterparts, studies of competition for plasma removal were undertaken: the remnant-like emulsion labeled with [3H]triolein was injected sequentially twice in the carotid arteries of rats to compare the clearance of remnant-like emulsion of the second injection with the first (control). Prior to the second injection, a large bolus of the chylomicron-like emulsion or rat lymph chylomicron was injected, to check the hypothesis that remnant generated from chylomicron-like emulsion or natural chylomicrons could compete with and displace remnant-like emulsion particles from their tissue receptor sites. Experiments were also performed in rats treated with Triton WR-1339, to block the generation of remnants. Results showed that remnants derived from either natural chylomicrons or chylomicron-like emulsion both strongly competed with the remnant-like emulsion. In contrast, when transformation of remnants was prevented by Triton, the undegraded particles of chylomicron-like emulsion or natural chylomicron were unable to compete with or displace remnant-like emulsion from its sites of removal from the plasma. In agreement with plasma clearance data, the hepatic uptake of the remnant-like emulsion was inhibited by the surplus dose of natural chylomicrons. In contrast, the spleen uptake was unaffected by it.
Oliveira
H C
HC
Heart Institute (INCOR), São Paulo University Medical School Hospital, Brazil.
Hirata
M H
MH
Redgrave
T G
TG
Maranhão
R C
RC
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002788:Cholesterol Esters / Q000378:metabolism; D002914:Chylomicrons / Q000097:blood / Q000378:metabolism*; D004655:Emulsions; D008099:Liver / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D009132:Muscles / Q000378:metabolism; D051381:Rats; D013154:Spleen / Q000378:metabolism
D002788:Cholesterol Esters; D002914:Chylomicrons; D004655:Emulsions