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Differences in Purine Metabolite Concentrations in the Diet of Managed and Free-Ranging Common Bottlenose Dolphins (Tursiops truncatus)
Abstract: Ammonium urate nephrolithiasis has been reported in common bottlenose dolphins (Tursiops truncatus) managed under human care but rarely occurs in free-ranging dolphins. In terrestrial mammals, including human beings, consumption of purine-rich seafood may predispose to urate urolith formation because purines are metabolized and excreted in urine as urate ions. Dolphins consume a piscivorous diet, but the purine content of their diet is unknown. Free-ranging dolphins consume live, temperate-water fish, whereas managed dol-phins consume frozen, stored, and thawed cold-water species that dolphins would probably not encounter in the wild. Purine metabolite concentrations vary with species and cold storage methods, so the purine intake of managed and free-ranging dolphins may differ. The concentrations of eight purine metabolites were measured in fresh frozen fish species commonly consumed by free-ranging dolphins and in seven frozen, stored, and thawed fish and squid species commonly consumed by managed dolphins. Total purine content was cal-culated for two model diets typically consumed by managed dolphins and a model diet reported to be consumed by bottlenose dolphins in Sarasota Bay, Florida. Total and individual purine metabolite concentrations differed significantly (p < 0.05) among individual species and among model diets. The mean total purine content of model managed dolphin diets was twice that in the model free-ranging dolphin diet. Inosine and IMP were measured because they can convert to hypoxanthine during frozen storage. Hypoxanthine concentrations were higher relative to inosine and IMP in managed species after frozen storage than in unstored free-ranging species (p < 0.05). These differences may explain the higher prevalence of ammonium urate nephrolithiasis in some managed dolphins compared to free-ranging dolphins and implies that the purine intake of some managed dolphins can be decreased by altering the proportions of species fed. Further research is needed, however, to determine whether such a change prevents ammonium urate nephrolith formation in dolphins.
Key Words: diet, kidney stones, ammonium urate nephroliths, IMP, inosine, hypoxanthine, purines, bottlenose dolphins, Tursiops truncatus
Document Type: Research Article
Page Numbers: 618-628