Immunocytochemical Identification of Endocrine Cells in the Pancreas of the Fruit Bat,Rousettus aegyptiacus

The fruit bat,Rousettus aegyptiacus,is able to absorb large amounts of glucose in very short periods of time. This ability is partly reflected by the structure of the gastrointestinal tract and pancreas. The aim of this study was to confirm preliminary histochemical studies of the bat pancreas and to identify and quantitate endocrine cells by immunocytochemical techniques in order to understand the ability of the bat to absorb these large amounts of glucose. Endocrine cells were distributed in islets throughout the gland and also occurred as discrete cells in the exocrine ducts. Three-dimensional reconstruction and quantitation showed that the endocrine component of the pancreas occupied 9.1% of the total volume. This is far more than that reported in any other species. Four endocrine cell types were demonstrated. Insulin (β) cells (51.4%) were located throughout the islet and extended between the glucagon (α) cells (30.6%). Somatotostatin (δ) cells (8.8%) and pancreatic polypeptide (PP) cells (17.1%) were irregularly scattered throughout the islets. While the percentage of α, β, and δ cells was similar to that in other species, the percentage of PP cells was higher. The high percentage of endocrine tissue found in the pancreas of the fruit bat may reflect metabolic adaptations involved in the absorption of the high carbohydrate diet of this animal.