In experimental mice, phenylhydrazine (PHZ; 60 mg/kg body weight; Sigma Chem, St. Louis, MO) was injected intraperitoneally for 2 consecutive days.

Blood was drawn from healthy donors using 3.13% sodium citrate as the anticoagulant (1: 5, v/v). Cells were isolated using isoosmotic phosphate-buffered saline (PBS, pH 7,4), microcrystalline cellulose and Lu-cellulose (1: 1, w/w) as described by Beutler et al. Red blood cells were suspended in PBS and preincubated in glass test-tubes in a shaking water bath for 1 hr at 37C, after which haematocrit was adjusted to 2.5% by adding PBS. Samples containing hemoglobin were adjusted to 8 mg/ml hemoglobin in PBS, i.e. a concentration comparable to that used in experiments with red cells. Varying amounts of phenylhydrazine, ranging from 0.5 to 50 mM were added to the red blood cell or hemoglobin samples. Then 3 ml of each sample was aliquoted into 10 ml headspace vials, and the vials were immediately sealed with special air-tight rubber septums. Headspaces were flushed with hydrocarbon-free synthetic air for 2 min in order to replace laboratory air containing small amounts of hydrocarbons. The sealed samples were then incubated in a shaking water bath at 37C. After certain periods, 1 ml of the gas phase was drawn with a gas-tight syringe and injected into the gas chromatograph.