Fast transport kinetics of 51Cr (VI) into red blood cells (RBCs) in vitro were studied. No significant species differences were found between RBCs of man and rat. The uptake of 51Cr (VI) by RBCs in whole blood was composed of two different first order processes of different velocities (apparent t 1/2 of 22.7 s and 10.4 min for man and 6.9 s and 10.1 min for rat, respectively). However, even after longer time periods a fixed portion of approximately 15% of the administered dose remained in the plasma and did not penetrate into RBCs Over the entire concentration range studied (10 microM-50 mM), the fast initial uptake followed Michaelis-Menten kinetics. The maximal capacity of this Cr(VI) transport into RBCs of man and rat was 3.1 X 10(8) CrO4(2-) ions X cell-1 X min-1 and 2.5 X 10(8) CrO4(-2) ions X cell-1 X min-1, respectively. It is likely that Cr(VI) is transported into RBCs via a physiological anion carrier ("band-3-protein").

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The pharmacokinetics of ethylene and 1,3-butadiene were studied in male Sprague-Dawley rats by use of a closed inhalation chamber system. Both compounds showed saturable metabolism when untreated rats were used. "Linear" pharmacokinetics applied at exposure concentrations below 800 ppm ethylene and below 1,000 ppm 1,3-butadiene. A constant elimination rate, indicative of metabolic saturation, occurred at concentrations higher than 1,000 ppm ethylene or 1,500 ppm 1,3-butadiene. Pretreatment with aroclor 1254 (polychlorinated biphenyls) increased Vmax for both compounds. For 1,3-butadiene, no saturation of metabolic capacity was observed with exposure concentrations up to 12,000 ppm when the rats were pretreated with aroclor 1254. A comparison with previous studies on ethane and n-pentane suggested that introduction of a double bond into a saturated aliphatic hydrocarbon increased the rate of metabolism under conditions in vivo.