Purineolytic capacity response of Nephrops norvegicus to prolonged emersion: an ammonia detoxification process

Under prolonged (>24 h) emersion, Norway lobster Nephrops norvegicus changed purineolytic pathways in response to increased levels of circulating ammonia. Haemolymph levels of urea and uric acid more than doubled during emersion, but xanthine oxidase was not detected, even after 72 h emersion. Xanthine dehydrogenase (XDH) was the only form of xanthine oxidoreductase detected, so the metabolic costs of producing uric acid would have been relatively small. Although ammonia, urea, uric acid and XDH all accumulated in the haemolymph during emersion, the relative proportions of ammonia and urea stayed the same at all times, which suggests the presence of enzymes from the uricolyic pathway (e.g. uricase and urease). Supranormal ammonia effluxes occurred almost immediately following re-immersion in amounts that indicate a high degree of hypoxia tolerance under emersion and that this is negatively related with the prevailing temperature. We conclude that N. norvegicus has purineolytic capacity and, under prolonged hypoxia, produces purines de novo as an ammonia-detoxification strategy that has probable survival value for a benthic burrowing species that may experience periods of severe hypoxia.