Neural and endocrinological regulation on the mucosal defence system in fish intestine

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In order to detect IgM producting cells in the gut cf rainbow trout by in situ hybridization, specific primer for membrane-binding IgM (mIgM) and secretory IgM (sIgM) was prepared and to paraffin sections, respectively. Cells expressing sIgM were distributed very scarcely in the submucosal region in the intestine. mIgM producing cells were to be detected, probably due to low level of its expression. These results suggest that non-specific defence molecules play more significant roles in fish alimentary canals. Congerin, a proto-type galectin purified from skin mucus cf Japanese conger is also distributed in the upper digestive tract of conger. In the current study it is clarified by western blotting that congerin reaches intestinal lumen. Digestion test using homogenates of conger stomach exhibited that congerin were degraded only partially even after 6 hours, while bovine serum albumin was completely digested within 30 min. These results indicate that congerin secreted from the digestive tract can successfully arrive to and function in the intestinal lumen of anger as defensive agents. Temperature stress induced decrease of congerin in the integument. However, intraperitoneal administration of cortisol showed no effect on the congerin contents. This indicates that congerin suction or secretion is regulated by unknown factors other than cortisol. On the other hand, congerin content in the upper digestive tract was not changed significantly under the same condition. This indicates that club cells, which produce congerin, in the skin and the upper digestive tract are regulated in the different way.