Kinetic Analysis Shows That Iron Deficiency Decreases Liver Vitamin A Mobilization in Rats1,2

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In view of evidence that nutritional status of iron and vitamin A may affect the other nutrient's metabolism, we used model-based compartmental analysis to examine effects of iron deficiency on whole-body vitamin A dynamics in rats. Weanling male Sprague-Dawley rats were fed the AIN93G diet with 2.5 nmol retinyl palmitate/g and either 45 [control (CN)] or 4 μg/g Fe [iron-deficient (ID)] for 8 wk. ID rats consumed food ad libitum; CN rats were food-restricted so that their body weights were the same as ID rats. Two rats/group were killed; liver vitamin A was determined and used for vitamin A balance calculations. [3H]Retinol-labeled plasma was administered intravenously to remaining rats, and 27 serial blood samples were collected for 7 wk. At killing, plasma vitamin A was 0.52 ± 0.12 (ID, n = 5) vs. 1.34 ± 0.12 μmol/L (CN, n = 6; P < 0.001), and liver vitamin A was 809 ± 94 (ID) vs. 112 ± 24 nmol (CN, P < 0.001). Plasma tracer data were fit to a three- or four-compartment model using the Simulation, Analysis and Modeling computer program and kinetic parameters were calculated. Vitamin A transfer rate between the retinyl ester storage pool [14 ± 3 (ID) vs. 24 ± 4 nmol/d (CN), P < 0.05] and plasma was lower in ID rats. Vitamin A remained longer in the body [44 ± 11 (ID) vs. 22 ± 3 d (CN), P < 0.05]. Adjusted mean disposal rate was lower in ID (10.0) than CN rats (19.9 nmol/d), as was estimated vitamin A absorption efficiency [58% (ID) vs. 76% (CN)]. Our results suggest that iron deficiency inhibits mobilization of vitamin A stores and may decrease the absorption and irreversible utilization of vitamin A.

Key words:

iron deficiency
vitamin A kinetics
simulation, analysis and modeling
rats

Abbreviations used:

CN
control
FCRp
plasma fractional catabolic rate
fdose
fraction of the injected dose
ID
iron-deficient
L(I,J)
fractional transfer coefficient
R(I,J)
transfer rate
RBP
retinol-binding protein
TBV
total blood volume
TMMP-retinol
all-trans-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl-2,4,6,8-nonatetraen-1-ol.

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1

Presented in part at Experimental Biology 99, April 1999, Washington D.C. [Green, M. H., Jang, J.-T. & Beard, J. L. (1999) Iron deficiency affects vitamin A kinetics in rats. FASEB J. 13: A867 (abs.)].

2

Supported by a grant from the Inter-College Graduate Program in Nutrition, The Pennsylvania State University.