Metabolism of apolipoprotein A-IV in rat.
The metabolism of apolipoprotein A-IV (apo-IV) has been investigated in the rat. In this animal species, apoA-IV is a major protein constituent of plasma HDL and lymph chylomicron. The apolipoprotein is also present in the lipoprotein-deficient fraction (LDF) of plasma and lymph. In vivo studies with the radioiodinated protein showed the apoA-IV does not exchange freely between HDL and LDF and that LDF apoA-IV had a faster catabolism than HDL apoA-IV. ApoA-IV in chylomicrons is a direct precursor of apoA-IV in plasma HDL but not of that in LDF. On the other hand lymph LDF apoA-IV is an important precursor of plasma LDF apoA-IV. Transfer of apoA-IV from plasma to lymph is negligible, and since most of apoA-IV in lymph is present in LDF, we speculate that LDF apoA-IV is the major apoA-IV secretory product of the intestine. Studies aimed at identifying the site of catabolism of apoA-IV utilizing either radioiodinated or [14C]sucrose labelled apoA-IV, gave results consistent with the view that the liver plays a major role. When tested, human apoA-IV behaved in vivo in rat as the autologous protein. These findings, together with others previously published (Ghiselli, G. et al. (1987) J. Lipid Res. 27, 813-827), support the conclusion that the plasma metabolism of apoA-IV is remarkably similar in rat and human. We speculate that in mammals the rapid plasma catabolism of apoA-IV is mediated by an efficient uptake by the liver.
Ghiselli
G
G
Baylor College of Medicine, Houston, TX.
Crump
W L
WL
Musanti
R
R
Sherrill
B C
BC
Gotto
A M
AM
D000818:Animals; D001054:Apolipoproteins A / Q000378:metabolism*; D002850:Chromatography, Gel; D002914:Chylomicrons / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008196:Lymph / Q000378:metabolism; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains
D001054:Apolipoproteins A; D002914:Chylomicrons; C022205:apolipoprotein A-IV