الفهرس 
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Abstract
Fish pancreatic islets have previously been examined in representatives of only 14 of 32 orders of euteleosts and 24 of the 391 families. Moreover, fish islets may introduce an economical source for islet transplantation as a cure for Diabetes mellitus, because of their hypoxia tolerance and ease of manual separation. Therefore, it could be clearly seen that fish pancreatic islets deserve some more attention than usual, not only for biological objectives such as classification, phylogenic and ontogenetic studies, but also for their expected importance as a therapeutic tool for curing one of the most complicated diseases all over the world, diabetes. It was the aim of the present study to get some information on the biology, comparative anatomical and histological structure of pancreatic islets of some teleost fishes that live in the Egyptian waters. Because of the vitality of the islet transplantation subject, it was the second aim of the present study to compare the pancreatic islet tissue (Brockmann bodies) of some fishes that live in our Egyptian local environment for their suitability for transplantation. Nine types of bony fishes were collected from the Egyptian water: Bagrus bajad [order: siluriformes, family: bagridae ], Clarias anguillaris [order: siluriformes, family: clariidae], Synodentis schall [order: siluriformes, family: mochocidae ], Cyprinus carpio [order: Cypriniformes family: cyprinidae ], Oreochromis niloticus [order: Perciformes, suborder: percoidei, family: cichlidae ], Mugil cephalus [order: Perciformes, suborder: mugiloidei, family: mugilidae], Sparus auratus [order: Perciformes, suborder: percoidei, family: sparidae], Argyromus regium [order: Perciformes, suborder: percoidei, family: sciaenidae ], Lutjanus flulvialemma [order: Perciformes, suborder: percoidei, family: lutjanidae]. The nine investigated fishes belong to 3 orders: siliriformes, cypriniformes and perciformes. The gross feature of the siliriform fishes was the presence of compact tetrapodlike pancreas, in addition to a seemly large islet in Bagrus bajad and Synodentis schall, but not in Clarias anguillaris. The cypriniform, Cyprinus carpio, was characterized by the partition of BB by thick fibrous strips into several smaller isletlike structures, giving an indication that the BB is a collection of several small islets. The gross feature of the endocrine pancreas of the investigated perciform fishes was the presence of one or two anatomically discrete BBs on the bile duct in addition to small satellites of small islets. Fibrous and exocrine layers of differing thickness were found around islet organs of different fish types. Staining the beta cells of islets from different fish types revealed the presence of insulinsecreting cells in all examined types but with different ratios related to the whole mass of the islets. Also, there were different patterns of clustering of these cells and different locations within the islets. Ultrastructural examination of the Brockmann bodies revealed the presence of the four cell types as in mammalian islets. Insulinsecreting beta, glucagonsecreting alpha, somatostatinsecreting delta and the pancreatic polypeptide (PP) cells were identified. Characters of every cell type were also similar to that in mammalian islets. Fasting blood glucose was measured in the different fish models. Except for Synodentis schall and Mugil cephalus, the other fish types were in the range of human fasting blood glucose level. However, all studied fish types, except Clarias anguillaris, were glucose intolerant. After performing an intraperitoneal glucose tolerance test (ipGTT), this study indicates certainly that teleost fish clear a glucose load more slowly than mammals. There is a great interest in the fact that human islets are less sensitive than rodent islets to alloxan, a beta cell toxin. Regarding species other than rodents and humans, not much is known about differences in islet susceptibility to this toxin. The results of the present study revealed that all investigated fishes are susceptible to alloxan toxicity. This susceptibility was dosedependent and differed from fish type to type. Siliriform fishes, especially Clarias anguillaris, were the least sensitive to alloxan than perciform fishes. Oreochromis niloticus was the most sensitive fish to alloxan. Human insulin was able to significantly reverse the alloxaninduced hyperglycemia in the different fishes. Only one unit of human insulin was able to reverse hyperglycemia in all investigated fishes. Moreover, it caused hypoglycemia in some instances. Thus, fishes seem to be responsive to human insulin and their cellular insulin receptors can recognize and bind to human insulin. The present study has its impact for islet transplantation. It could be concluded that there are many criteria to say that a fish can be used as an islet donor. This fish should: 1. be tropical, 2. be easy to rear, 3. have blood glucose background similar to that in man, 4. have large islets, easy to be separated, 5. have pure islets with the least contamination with fibrous and exocrine tissues, 6. have satisfactory insulin output, and 7. tolerable islets to the different environmental factors found in the recipient after engraftment. After comparison of the different fish types, it may be concluded that Oreochromis niloticus may be the most suitable isletdonor fish among the studied types.