Quantitative Studies on Isolated Pancreatic Islets of Mammals. 5-Nucleotidase and Adenosine Triphosphatase Activities in Normal and Cortisone-Treated Rats
Chemical micromethods and histochemical staining were employed in analyses of the adenosine monophosphate- and triphosphate-splitting enzyme activities of the endocrine pancreas from normal and cortisonetreated rats. The following observations were made: 1. Histochemical staining revealed a marked AMP-5′-splitting enzymic activity in the islet β cells. 2. Dephosphorylation of AMP-5′ was maximal at about pH 7.1. It was considerably inhibited by nickel and fluoride ions, while a moderate activation was exerted by manganese ions. Substitution of AMP-5′ by equimolar concentrations of AMP-2′, AMP-3′ or sodium ′-glycerophosphate reduced the rate of enzymatic phosphate liberation by more than 80%. The properties of the AMP-5′- splitting activity in the islets are consistent with those previously recorded for 5-nucleotidase in other tissues. 3. Cortisone administration stimulated the AMP-5 ′-splitting activity in the islet homogenates, while there was a reduction of the rate of cleavage of ATP. These results may reflect an enzymatic adaptation to the higher functional state of the β cells characteristic in steroid-treated rats. (Endocrinology76: 315, 1965)