Enzyme histochemistry of the pancreatic islets in the duck with special reference to the two types of A cells

Abstract

1. Some enzymes in the pancreatic islets of the duck have been studied histochemically with special reference to the enzyme patterns of the silver positive A1 cells and the silver negative A2 cells. The characteristic topography of the endocrine pancreas of the duck made possible a direct identification of different types of islet cells in the cytochemically stained sections. 2. The islet B cells exhibited a strong reaction for alkaline phosphatases, the reactions for acid phosphatases being considerably weaker. Evidence for a specific glucose-6-phosphatase activity was obtained by the demonstration of a selective enzyme activity against 5 and 6-carbon sugar phosphates and α-glycerophosphate at a pH optimum of about 6.7. A positive reaction for adenosine triphosphatase might have been accounted for by unspecific alkaline phosphatase activity. Aminopeptidase or esterase activities were not found in the B cells, which, on the other hand, displayed pronounced positive reactions for diphosphopyridine nucleotide diaphorase, triphosphopyridine nucleotide diaphorase and β-hydroxybutyrate dehydrogenase, moderate reactions for glucose-6-phosphate dehydrogenase and lactic dehydrogenase and a weak reaction for succinic dehydrogenase. 3. The islet A1 and A2 cells showed an enzyme pattern quite different from that of the B cells. The A1 cells exhibited a conspicuously strong acid phosphatase activity contrasting against the weaker reaction in the A2 cells. The reaction for alkaline phosphatases remained negative except for a small fraction of weakly staining cells, and glucose-6-phosphatase or adenosine triphosphatase activities were not found in any type of A cell. In both the A1 and A2 cells there was a moderate esterase activity and the A1 cells at least exhibited a considerable aminopeptidase activity. As compared to the B cells the reactions for diaphorases and dehydrogenases were considerably weaker in the two types of A cells. However, the diaphorase activities as well as the reactions for lactic dehydrogenase and succinic dehydrogenase appeared somewhat stronger in the A1 than in the A2 cells. 4. The results are discussed with special regard to present knowledge of the enzyme pattern and metabolic properties of mammalian islet cells.