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Dehydrouramil hydrate hydrochloride (DHU) is an analogue of alloxan which retains the in vivo diabetogenic activity of alloxan but, in contrast to alloxan, is stable in aqueous media at physiological pH. Using rat islets of Langerhans, we have studied the acute effects of DHU on B cell function. Glucose-stimulated insulin release was markedly inhibited by DHU, the concentration of DHU giving 50% inhibition (I50) was 1 mmol/l; this was lowered to 0.5 mmol/l when the islets were exposed to DHU for 5 min before elevation of glucose concentration. The basis for this change appeared to be a protective effect of glucose, since the inclusion of 3-0-methylglucose during re-incubation with DHU also attenuated the subsequent inhibition of glucose-stimulated insulin release. The inhibitory effect on glucose-stimulated insulin release of a 5-min exposure to DHU persisted throughout a subsequent 120-min period in the absence of DHU. DHU also inhibited insulin release stimulated by mannose (20 mmol/l) or by 2-ketoisocaproate (20 mmol/l) with I50 of 1 and 0.5 mmol/l respectively. Concentrations of DHU up to 1 mmol/l had no significant effect on islet glucose oxidation or ATP content; 5 mmol/l DHU did not affect the rate of glucose oxidation, but lowered the ATP content by 30% without pre-incubation and by 60% in islets pre-incubated for 5 min with DHU before addition of glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Ring‐chain tautomeric equilibria in the 1,3,4,6‐tetraketone series 1 have been examined and the identification of the chain‐form 2 and hydroxyfuranone 3 has been accomplished from 1H‐nmr spectra; the relative contribution of the two depends on the structure and also on the solvent. Conversions of 1 into 3(2H)furanones 4 and 5 involving the cyclic tautomer 3 are described.