Monoamines in Pancreatic Islets of Guinea Pig, Hamster, Rat, and Mouse Determined by High Performance Liquid Chromatography

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Abstract
Previous studies on the occurrence of catecholamines and serotonin in pancreatic islets using various histochemical and chemical methods have given widely different results. We therefore performed a comparative analysis of these amines in whole pancreas and islet tissue from hamster, guinea pig, rat, and mouse by the use of high performance liquid chromatography. Whole pancreas of guinea pig, hamster, and rat had a norepinephrine concentration of approximately 1.1 μmol/kg of pancreatic wet weight. The mouse pancreas had less than one-half of that concentration. Epinephrine and dopamine concentrations were on the order of 0.02 μmol/kg of pancreatic wet weight in all four species. The serotonin concentration was 2.1 μmol/kg of pancreatic wet weight in the guinea pig pancreas and approximately 0.2 μmol/kg in the other three species studied. The catecholamine concentrations were much higher in the pancreatic islets than in the exocrine pancreas. Thus, the norepinephrine concentration was approximately 35 μmol/kg of islet wet weight in hamster islets and 5–10 μmol/kg in rat, guinea pig, and mouse islets. The epinephrine concentration in islet tissue ranged between 1 and 7 μmol/kg of islet wet weight and the dopamine concentration between 0.5 and 4 μmol/kg except for guinea pig islets (12 μmol/kg). The islet tissue in the mouse, rat, and guinea pig contained disproportionately more epinephrine and dopamine relative to norepinephrine than did the exocrine pancreas. Chemical sympathectomy (6- hydroxydopamine treatment) in the mouse reduced the norepinephrine and epinephrine concentrations in islet tissue to nondetectable levels, whereas the dopamine concentration was essentially unchanged, thus suggesting an extraneuronal source of this amine in addition to its occurrence in adrenergic nerves. The islets of hamster, rat, and mouse contained no serotonin, whereas guinea pig islets contained approximately 275 μmol/kg of islet wet weight. We conclude that, although species differences exist, the pancreatic islets have markedly higher levels of catecholamines than the exocrine pancreas, and that serotonin occurs in the exocrine pancreas of all four species studied but in the endocrine pancreas only in the guinea pig.

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