1. Department of Environmental & Occupational Health, School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania 15238.
2. Department of Pharmacology, School of Medicine University of Pittsburgh, Pittsburgh, Pennsylvania 15238.
3. On leave from the Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Science, St. Petersburg, Russia 194223.
4. Department of Medicine, School of Medicine University of Pittsburgh, Pittsburgh, Pennsylvania 15238.