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© 1998 Oxford University Press
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Use of Model-Based Compartmental Analysis to Study Effects of 2,3,7,8-Tetrachlorodibenzo-p-dioxin on Vitamin A Kinetics in Rats1,2
*The Institute of Environmental Medicine, The Karolinska Institute Stockholm, Sweden
Nutrition Department, The Pennsylvania Stare University University Park Pennsylvania 16802
Received September 23, 1997; accepted March 30, 1998
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic, widespread environmental contaminant that has dramatic adverse effects on the metabolism of vitamin A. We used model-based compartmental analysis to investigate sites and quantitative impacts of TCDD on vitamin A kinetics in rats given an oral loading dose of TCDD in oil (3.5 µg/kg) followed by weekly maintenance doses (0.7 µg/kg) or oil only. [3H]retinyl in its plasma transport complex (experiment 1) or lymph containing chylomicrons labeled mainly with [3H]retinyl esters (experiment 2) were administered iv, and tracer kinetics in plasma, liver, carcass, urine, and feces were measured for up to 42 days. TCDD treatment caused significant reductions in liver vitamin A levels and significant changes in tracer kinetics and tracer excretion. A four-compartment model was used to fit tracer data for experiment 1; for experiment 2, compartments were added to describe the metabolism of newly absorbed vitamin A. The compartmental models predict that TCDD caused a slight delay in plasma clearance (via an increased recycling to plasma), and in liver processing, of chylomicronderived vitamin A. Models for both experiments predict that TCDD exposure did not affect the fractional uptake of plasma retinol from the rapidly turning-over extravascular pool, but it doubled the fractional transfer of recycled rethol from slowly turning-over pools of vitamin A to plasma The residence time for vitamin A was reduced by 70% in TCDD-treated rats, transfer into urine and feces was tripled, and vitamin A utilization rates were significantly increased. Since our results do not indicate that retino1 esterification is inhibited, we hypothesize that some of the significant effects of TCDD on vitamin A metabolism result from increased catabolism and mobilization of vitamin A from slowly turning-over pools (especially the liver).
Key Words: 2,3,7,8-Tetrachlorodibenzo-p-dioxin; TCDD; rat; vitamin A; model-based compartmental analysis; kinetics.
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