Vitamin D3 uptake by the isolated perfused rat liver from lipoprotein fractions is separate from cholesterol and triglyceride uptake.
Using the isolated perfused rat liver we examined the uptake of [14C] or [3H] vitamin D3 and [14C] triglycerides or [3H] cholesterol by the liver of normal rats, from different lipoprotein fractions, as measured by disappearance from the perfusate. When incorporated into chylomicrons only 43% of the vitamin D3 remained in the perfusate at 60 min (i.e. 57% uptake) as compared to 68% of the triglycerides (i.e. 32% uptake). When added on very low density lipoproteins (VLDL) at 60 min 37 +/- 3% (n = 6) of the vitamin D3, 38 +/- 2% of the cholesterol (n = 3) (P NS), and 83 +/- 4% of the triglycerides (n = 3) remained in the perfusate (P less than 0.0005 for cholesterol:triglycerides and vitamin D3:triglycerides). For high density lipoprotein fraction (HDL) isolated perfused livers were studied with and without albumin present in the perfusate. Without albumin 19 +/- 8% (n = 3) of the vitamin D3 and 43 +/- 8% (n = 3) of the cholesterol remained in the perfusate at 60 min. The results with albumin present were 40 +/- 1% (n = 5) of the vitamin D3 and 63 +/- 4% (n = 5) of the cholesterol at 60 min (P less than 0.0005). The cholesterol:cholesterol ester ratio of the VLDL fraction was 8.8:1 and of the HDL fraction 1:1.4. There was no metabolism of vitamin D3 during the 1 h perfusion. These results suggest that vitamin D3 is in equilibrium with the lipoprotein surface, and the hepatic uptake of vitamin D is a surface phenomenon independent of lipoprotein metabolism.
Ziv
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Bar-On
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Silver
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D000818:Animals; D002762:Cholecalciferol / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism; D002914:Chylomicrons / Q000378:metabolism; D066298:In Vitro Techniques; D008074:Lipoproteins / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000378:metabolism; D008079:Lipoproteins, VLDL / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D051381:Rats; D014280:Triglycerides / Q000378:metabolism*
D002788:Cholesterol Esters; D002914:Chylomicrons; D008074:Lipoproteins; D008075:Lipoproteins, HDL; D008079:Lipoproteins, VLDL; D014280:Triglycerides; D002762:Cholecalciferol; D002784:Cholesterol