The microanatomy of canine islets of Langerhans: implications for intra-islet regulation

Abstract

In recent years models for the internal ("intra-islet") regulation of hormone secretion have been proposed to explain how different islet cells might regulate each other by means of their respective secretory peptides. Models that emphasize the importance of a directed intra-islet blood flow and sequence of perfusion of islet cells rely on a certain type of islet microanatomy and vascular supply. The experimental studies underlying these models have partly been performed in dogs. To extend the incomplete morphological knowledge of the canine endocrine pancreas both canine islets of Langerhans and extrainsular cells have been analysed in immunostained serial semithin (0.5 microns) sections. In addition to their occurrence within islets of Langerhans, all endocrine cell types are also found at extrainsular sites (about 9% of all endocrine cells) where they are distributed in different quantities among the epithelial lining of exocrine acini or excretory ducts and the connective tissue. There are continuous transitions from single extrainsular cells to small mono- and polycellular cell groups to islets. In a comprehensive analysis of whole islets, including computer-assisted three-dimensional reconstructions, the size, shape and vascularization of the islets as well as their cellular composition and the microtopology of islet cells have been studied. We have found marked intra- and inter-islet heterogeneities of the parameters investigated that are not compatible with concepts of a uniform and directed vascular perfusion of the various islet cell populations. Instead, their paracrine regulation may occur primarily via hormonal secretion into the intercellular spaces or vascular hormonal delivery to adjacent cells.

The Comparative Anatomy of Islets

“…The dog β-cells generally occupy the central portion of the islets but are also found as single cells in the exocrine pancreas (Wieczorek et al 1998), while the α-cells are generally in the periphery but also found centrally in some islets. The δ-cells are generally mixed in the islets while PP cells appear as single cells or groups (Gapp et al 1985;Redecker et al 1992). The endocrine pancreas of the Cape fur seal showed very similar morphology to what is observed in other carnivorous species like the dog and cat, and this shows a central core of β-cells surrounded by glucagon, somatostatin, and PP cells.…”

Secretory granules of hypophyseal and pancreatic endocrine cells contain proteins of the neuronal postsynaptic density

“…Rabbit antibodies against fusion proteins expressed from IRSp53 or ProSAPiP1 cDNAs were as described previously Wendholt et al 2006) and were diluted between 1:500 and 1:1,000. Details of the antibodies used for the detection of pancreatic and hypophyseal hormones were as given in earlier studies (Cetin et al 1993;Redecker et al 1992Redecker et al , 1995. For the detection of growth hormone (GH) at the ultrastructural level in double-labeling experiments, a goat anti-GH antiserum (L-20) was used (Santa Cruz Biotechnology, Santa Cruz, USA).…”

Simplified Method to Isolate Highly Pure Canine Pancreatic Islets

“…8 Histology studies show similar amounts of collagen in pancreata from humans and dogs, significantly higher than those from rats. 9 Importantly, dog β cells occupy large areas of the islet core as well as the periphery, 10 similar to human but not rodent islets. 11 At the functional level, canine and human islets, in contrast to rodent islets, have similar ion-channel regulation of the electrical activity induced by glucose in β cells 12 and thus can be a helpful tool for islet research.…”