ADENYL CYCLASE AND PHOSPHODIESTERASE ACTIVITY IN THE ISOLATED ISLETS OF LANGERHANS OF OBESE MICE AND THEIR LEAN LITTER MATES: THE EFFECT OF GLUCOSE, ADRENALINE AND DRUGS ON ADENYL CYCLASE ACTIVITY

Abstract

SUMMARY Radiometric estimations of adenyl cyclase and cyclic AMP (cAMP) phosphodiesterase showed significantly higher enzyme activities in the islet tissue of obese-hyperglycaemic mice than in that of their normal litter mates, but the ratios of the two enzymes in both types of islets were found to be the same, i.e. 1:1. Adenyl cyclase and phosphodiesterase activity increased linearly with incubation time and protein concentration. Sodium fluoride (10 mmol/1) increased cyclase activity in the islets of obese mice by 33·4%; theophylline (10 mmol/1) in the presence of cAMP (1 mmol/1) reduced phosphodiesterase activity by almost 100%. Glucose (2 g/1) reduced, while adrenaline (10−5 mol/1) increased cyclase activity in islets from both normal and obese animals. An evaluation of the effects of α- and β-adrenergic receptor stimulating and blocking agents on islets of both normal and obese mice showed the stimulation of adenyl cyclase to be a β-adrenergic receptor function and the inhibition an α-adrenergic receptor function. The possible role of the adenyl cyclase system in diabetes mellitus and insulin secretion is discussed.