Plasma transport and tissue distribution of beta-carotene, vitamin A and retinol-binding protein in domestic cats

The objective of this study was to determine retinol, retinyl asters and re tinol-binding protein (RBP) as well as carotenoids in plasma, urine, liver and kidneys of randomly selected domestic cats. Retinol (240 +/- 64 ng/ml, mean +/- S.D.) represented one-third of total retinyl esters (736 +/- 460 n g/ml) in plasma. Retinyl esters were stearate, palmitate and oleate represe nting 61 +/- 6, 36 +/- 13 and 5 +/- 3% of total retinyl esters; respectivel y. In half of the cats, retinyl esters (22 +/- 21 ng/ml) were found in the urine. Vitamin A in the livers (4317 +/- 1956 mug/g) was significantly high er than in the kidney cortex and medulla (14.16 +/- 8.92 and 7.59 +/- 4.57 mug/g, respectively, both P < 0.001). RBP was detected in the plasma but no t in the urine. Immunoreactive RBP was observed in hepatocytes and in the c ells of the proximal tubules. beta -Carotene was present in plasma but neve r in tissues. The results show that similar to canines differences in vitam in A metabolism in cats are related to the occurrence of retinyl esters in plasma. They differ, however, with regard to the tissue distribution of bet a -carotene and the excretion of vitamin A in the urine. (C) 2001 Elsevier Science Inc. All rights reserved.