Pancreatic Secretion of Electrolytes and Water

The three-dimensional microanatomy of the pancreatic duct system in the Japanese monkey, Macaca fuscata, with special reference to fine proximal passages of a high species-specificity

We have previously shown the duct system in the rat pancreas to consist of two parts: a fine proximal (intercalated) duct and thicker distal (intralobular and interlobular) duct, with the latter part displaying morphological signs indicative of a bicarbonate-rich fluid secretion. In this study the pancreatic duct system in the Japanese monkey Macaca fuscata was observed by scanning electron microscopy after the hydrolytic exposure of cell surfaces as well as by transmission electron microscopy of ultrathin sections. Cellular expression of the water channel aquaporin 1 (AQP1) was also examined immunohistochemically. In contrast to the segmented duct system in the rat, all the duct cells in the monkey pancreas consistently displayed rich mitochondria in the cytoplasm, elaborate interdigitations of cell processes, and an intense immunoreactivity for AQP1 on the apical and basolateral cell membrane to favor active ion transport and osmotic water movement across the epithelium. Both the existence of secretory canaliculi and basal trabeculae in the duct epithelium and randomized localization of primary cilia on the luminal cell surfaces were demonstrated for the first time in monkeys, and the physiological implications of these phenomena are discussed.