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  • 1
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The nitrogen metabolism and excretion patterns of the grunting toadfish Allenbatrachus grunniens and the effects of salinity on these processes were examined. Individuals of A. grunniens were subjected to several experimental treatments, including variable salinity (2 to 30), high pH (8·5 compared to 7·0 for controls), high environmental ammonia (10 mM) and confinement to small water volumes, and measurements were made of activities of selected enzymes of nitrogen metabolism, ammonia and urea excretion rates, and tissue and plasma contents of ammonia, urea and amino acids. Activities of key ornithine-urea cycle enzymes were rather low (e.g. liver carbamoyl phosphate synthetase III activity was 0·001 μmols min−1 g−1), and A. grunniens consistently demonstrated a low capacity for urea excretion despite significant elevations of plasma and tissue ammonia contents by the high pH and high ammonia treatments. This species could thus be categorized as ammoniotelic. Total free amino acid contents in plasma and tissues were increased by the high pH and high ammonia treatments, but no patterns were discerned in individual amino acids that would indicate any preferential accumulation (e.g. alanine and glutamine) as has been noted previously in several semi-terrestrial fish species. Thus, it appeared that A. grunniens was not unusual in its patterns of nitrogen metabolism and excretion in comparison to other ‘typical’ teleosts. Furthermore, manipulation of salinity had no major effects on nitrogen excretion in either this species or in comparative studies with the ureotelic gulf toadfish Opsanus beta. The results are discussed in the context of the broader pattern of nitrogen metabolism and excretion in the Batrachoididae.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: There is growing evidence of the brain's ability to increase its reliance on alternative metabolic substrates under conditions of energy stress such as starvation, hypoxia and ischemia. We hypothesized that following traumatic brain injury (TBI), which results in immediate changes in energy metabolism, the adult brain increases uptake and oxidation of the alternative substrate β-hydroxybutyrate (βHB). Arterio-venous differences were used to determine global cerebral uptake of βHB and production of 14CO2 from [14C]3-βHB 3 h after controlled cortical impact (CCI) injury. Quantitative bioluminescence was used to assess regional changes in ATP concentration. As expected, adult sham and CCI animals with only endogenously available βHB showed no significant increase in cerebral uptake of βHB or 14CO2 production. Increasing arterial βHB concentrations 2.9-fold with 3 h of βHB infusion failed to increase cerebral uptake of βHB or 14CO2 production in adult sham animals. Only CCI animals that received a 3-h βHB infusion showed an 8.5-fold increase in cerebral uptake of βHB and greater than 10.7-fold increase in 14CO2 production relative to sham βHB-infused animals. The TBI-induced 20% decrease in ipsilateral cortical ATP concentration was alleviated by 3 h of βHB infusion beginning immediately after CCI injury.
    Type of Medium: Electronic Resource
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