Molecular Pharmacology, Vol 13, 598-605, Copyright © 1977 by the American Society for Pharmacology and Experimental Therapeutics

Inhibition of p-Chloromercuribenzoate- and Glucose-Induced Insulin Release in Vitro by Methylene Blue, Diamide, and tert-Butyl Hydroperoxide

¹ Department of Pharmacology, Institute of Pharmaceutical Sciences, University of Tuebingen, D-74 Tuebingen, and Department of Pharmacology, Toxicology, and Pharmacy, Faculty of Veterinary Medicine, University of Munich, 8 Muenchen, German Federal Republic

This investigation was designed to explore the possible role of NADPH and reduced glutathione in insulin secretion and their relationship to thiol groups located in the -cell membrane. We studied the effects of 2 µg/ml of methylene blue (an oxidant of NADPH), 0.1 mM diamide (an oxidant of GSH), and 2 mM tert-butyl hydroperoxide (a substrate of GSH peroxidase) on the release of insulin from isolated, perfused rat pancreas and pancreatic islets. p-Chloromercuribenzoate (a thiol reagent triggering insulin release supposedly by virtue of its action on superficial thiol groups in -cell membranes) was used at 0.1 mM to initiate insulin secretion from isolated, perfused rat pancreas, while isolated islets were stimulated to release insulin with 3 mg/ml of glucose. Both phases of p-chloromercuribenzoate-triggered insulin release were significantly suppressed by methylene blue, diamide, and tert-butyl hydroperoxide. Similarly, these substances inhibited glucose-stimulated insulin release from isolated islets. These results suggest that stimulation of insulin release by p-chloromercuribenzoate and glucose depends on the content of NADPH and GSH in the islets. It is postulated that thiol groups in the -cell membrane, which are thought to be related to insulin release, are kept in the reduced state via the following sequence of events:

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Note:
ACKNOWLEDGMENTS The authors wish to thank Miss I. Breuning and Mrs. I. Hagenloh for their skillful technical assistance. We are also indebted to Dr. O. Vitzthum of HAG AG for a generous supply of diamide, and to Professor Dr. A. Wendel for helpful advice.