[Individual differences in the vitamin A metabolism of the order Carnivora--a review].
Vitamin A transport in blood of most species in the order carnivora is fundamentally different from other animals and man. Very high levels of vitamin A in blood plasma of canines and mustelides are due to a high percentage of retinyl esters. These esters (basically retinyl palmitate and stearate) are transported nonspecifically bound to lipoproteins with very-low and low density lipoproteins representing the major fractions (about 70% of total vitamin A esters). A high percentage of retinyl esters could also be found in the families Ursidae, Procyonidae, Viverridae and Felidae in which total vitamin A in blood was low. In man and rat severe signs of vitamin A intoxication can be observed due to a similarly high percentage of nonspecifically bound vitamin A esters. No clinical or clinical-chemical signs of vitamin A intoxication were observed in the animals investigated. Because vitamin A esters are transported by lipoproteins, their blood levels are readily affected by dietary vitamin A supply as it is known to be the case for vitamin E. Furthermore, canines seem to be the only ones that excrete vitamin A as retinol and retinyl esters (basically retinyl palmitate) under physiological conditions with the urine. These fat-soluble metabolites of vitamin A are bound to a protein with a molecular weight between 50,000 and 125,000 Da which shows characteristics of a lipoprotein when subjected to ultracentrifugation or selective precipitation. Higher levels of vitamin A in organs and tissues, as well as the excretion of vitamin A with the urine, might be a consequence of the nonspecific binding of large amounts of retinyl esters to lipoproteins in blood.(ABSTRACT TRUNCATED AT 250 WORDS)
Schweigert
F J
FJ
Institut für Physiologie, Physiologische Chemie und Ernährungsphysiologie, Tierärztlichen Fakultät, Ludwig-Maximilians-Universität München.
Zucker
H
H
D000818:Animals; D001692:Biological Transport; D002335:Carnivora / Q000378:metabolism*; D004952:Esters; D008074:Lipoproteins / Q000378:metabolism; D011485:Protein Binding; D014801:Vitamin A / Q000493:pharmacokinetics*
D004952:Esters; D008074:Lipoproteins; D014801:Vitamin A
Besonderheiten im Vitamin A-Stoffwechsel der Ordnung Carnivora--Eine Ubersicht.