1. Chemical Industry Institute of Toxicology (K.W.G., L.S.L., S.C.M.), Research Triangle Park, North Carolina 27709
2. The Department of Pharmacology and Cancer Biology, Duke University Medical Center (J.M.H., D.P.M.), Durham, North Carolina 27710
3. The Department of Veterinary Physiology and Pharmacology, Texas A&M University (B.S., S.S.), College Station, Texas 77843