A COMPARTMENTAL MODEL DEPICTING SHORT-TERM KINETIC CHANGES IN SELENIUM METABOLISM IN EWES FED HAY CONTAINING NORMAL OR INADEQUATE LEVELS OFSELENIUM

Changes in Se metabolism were studied in ewes fed hay containing norma l or inadequate levels of Se. After intravenous injection of Se-75-sod ium selenite, blood, feces and urine were collected at different times , and the concentrations of labeled and unlabeled Se were determined. Ewes were killed 1, 5, 9 or 14 d after tracer injection, and tissues w ere obtained for determination of radioactivity and Se concentration. The data were fitted to a compartmental model using the SAAM/CONSAM co mputer program, and kinetic parameters and steady-state transport rate s were estimated. Daily Se intake (V-I) and fecal excretion (V-F) were significantly (P < 0.001) higher in the ewes fed normal hay (6.06 +/- 1.09 and 3.36 +/- 0.88 mu mol/d, respectively) than in those fed Se-d eficient hay (0.64 +/- 0.18 and 0.26 +/- 0.15 mu mol/d). The net absor ption (V,) of Se was significantly higher in ewes fed normal hay [3.19 +/- 0.82 mu mol/d by the balance method, V-a = V-I - (V-F - V-f) (V-f = endogenous fecal Se) and 1.05 +/- 0.38 mu mol/d by using the model (plasma entry rate, U(1))] than in those fed hay deficient in Se [0.57 +/- 0.33 mu mol/d (balance) and 0.28 +/- 0.08 mu mol/d (model)]. The efficiency of absorption [alpha = U(1) divided by V-i] was significant ly higher (0.46 +/- 0.19) in ewes fed Se-deficient hay than in those f ed normal hay (0.18 +/- 0.09). Simultaneous fitting of the tracer data of both the groups showed that changes in hepatic extraction and urin ary and fecal excretion were sufficient and necessary to account for t he kinetic differences observed between treatments.