An increase of uricogenesis in the Kuruma shrimp Marsupenaeus japonicus under nitrite stress

Kuruma shrimp Marsupenaeus japonicus Bate, under the stress of 0.36 and 1.39 mM nitrite at 30 per thousand (parts per thousand, g kg(-1)) for 48 h, were examined for nucleotide-related compounds, specific activities of xanthine dehydrogenase (XDH), xanthine oxidase (XOD), and uricase. The levels of total nucleotide-related compounds, including xanthine and hypoxanthine, in the gill increased directly with ambient nitrite, whereas the levels of total nucleotide-related compounds, including xanthine and hypoxanthine, in the hepatopancreas were inversely related to ambient nitrite. Specific activity of XOD in the hepatopancreas increased directly with ambient nitrite, whereas no significant difference in uricase activity in the hepatopancreas was observed among three treatments. In another experiment, M. japonicus, following 48 h exposure to 0.36 and 1.39 mM nitrite, were examined for ammonia, urea, and urate levels in tissues. Hemolymph urea and exoskeleton urate levels increased directly with ambient nitrite, whereas hemolymph urate and exoskeleton urea levels were inversely related to ambient nitrite. It is concluded that M. japonicus exhibited uricogenesis and uricolysis, and an increase of uricogenesis occurred for the shrimp under nitrite stress. Urate produced in the hepatopancreas was transported and accumulated in the epidermis, and removed along with the exoskeleton at the time of molting.