1. Department of Pharmacology (S.M.B., N.A., T.P., M.A.), Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
2. Center for Reproductive Sciences (F.X.), University of California, San Francisco, San Francisco, California 94143
3. Department of Pharmacology (S.O.), Max Planck Institute for Heart and Lung Research, 61231 Bad Nauheim, Germany
4. Women's Health Department (J.A.G.), Merck Sharp and Dohme Research Laboratories, 5340 BH Oss, The Netherlands