1. Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, Laboratory of Molecular Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville, Maryland 20850, Division of Neuroscience, Oregon Primate Research Center, Beaverton, Oregon 97006, and Peptide Research Laboratories, Tulane University, New Orleans, Louisiana 70112