Zinc and manganese contents of micro-dissected pancreatic islets of some rodents. A microchemical study in adult and newborn guinea pigs, rats, Chinese hamsters and spiny mice.

By a flameless atomic absorption spectrophotometry procedure, using a graphite furnace, it was possible to assay the contents of zinc and managanese in micro-dissected pancreatic islets of several rodents. Interest was focused upon the islets of guinea-pigs, due to the fact that guinea-pig insulin lacks a histidine residue in the B10 position of the molecule which normally binds zinc (or other heavy metals) in the hexamer formation, probably involved in the storage of insulin. Both the zinc and manganese contents were too low in the guinea-pig islet parenchyma to be reasonably involved in the storage of insulin in the beta-granules. Instead, it was suggested that guinea-pig insulin, like hagfish insulin, might crystallize without access to zinc or other heavy metals. Low zinc and manganese contents were also observed in newborn and diabetic guinea-pigs. The islet zinc content was high in the Wistar rat, the Chinese hamster, and the spiny mouse. No significant amounts of manganese were found in any of these kinds of islet parenchyma.