Inhalation pharmacokinetics based on gas uptake studies. V. Comparative pharmacokinetics of ethylene and 1,3-butadiene in rats.

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.