QUANTITATIVE STUDIES ON ISOLATED PANCREATIC ISLETS OF MAMMALS: ENZYMIC HYDROLYSIS OF NUCLEOSIDE DIPHOSPHATES AND p-NITROPHENYL PHOSPHATE IN NORMAL AND CORTISONE-TREATED RATS

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Abstract
SUMMARY Chemical micromethods and histochemical staining were employed for studies of the enzymic hydrolysis of inosine diphosphate (IDP) and adenosine diphosphate (ADP) and the non-specific acid phosphatase activity of the endocrine pancreas from normal and cortisone-treated rats. The following observations were made: 1. Enzymic dephosphorylation of IDP and ADP was maximal at about pH 8·0. Magnesium and manganese ions enhanced the phosphate liberation, the hydrolysis of ADP being more activated than that of IDP. A marked inhibition of enzyme activity towards either substrate was produced by sodium fluoride, sodium cyanide and ethylene-diaminotetraacetate. Acid phosphatase activity was maximal at about pH 5·5, a tendency for a second activity optimum was noted at about pH 4·0. Acid phosphatase activity was markedly inhibited by sodium fluoride, tartaric acid and formaldehyde. 2. Histochemical staining revealed marked enzyme activity towards IDP and ADP in the capillaries and walls of the large blood vessels throughout the pancreas, whereas the islet cells displayed a moderate reaction. The staining intensity was the same with IDP as with ADP. 3. Cortisone administration reduced the rate of cleavage of both IDP and ADP in both the endocrine and the exocrine pancreas, but the enzymic splitting of these substrates remained unchanged in the liver. Acid phosphatase activity was not influenced in any of these tissues by the steroid treatment.