1. Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060, Japan
2. Laboratory of Biopharmaceutics, Faculty of Pharmaceutical Sciences, Chiba University, Chiba 263, Japan
3. Laboratory of Infectious Diseases, Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060, Japan
4. Laboratory of Chemistry, Osaka City University Medical School, Abenoku, Osaka 545, Japan