title: Exposure to acute severe hypoxia leads to increased urea loss and disruptions in acid-base and ionoregulatory balance in dogfish sharks (Squalus acanthias).
abstract: The effects of acute moderate (20% air O2 saturation; 6-h exposure) and severe (5% air O2 saturation; 4-h exposure) hypoxia on N-waste, acid-base, and ion balance in dogfish sharks (Squalus acanthias suckleyi) were evaluated. We predicted that the synthesis and/or retention of urea, which are active processes, would be inhibited by hypoxia. Exposure to moderate hypoxia had negligible effects on N-waste fluxes or systemic physiology, except for a modest rise in plasma lactate. Exposure to severe hypoxia led to a significant increase in urea excretion (Jurea), while plasma, liver, and muscle urea concentrations were unchanged, suggesting a loss of urea retention. Ammonia excretion (Jamm) was elevated during normoxic recovery. Moreover, severe hypoxia led to disruptions in acid-base balance, indicated by a large increase in plasma [lactate] and substantial decreases in arterial pHa and plasma [Formula: see text], as well as loss of ionic homeostasis, indicated by increases in plasma [Mg(2+)], [Ca(2+)], and [Na(+)]. We suggest that severe hypoxia in dogfish sharks leads to a reduction in active gill homeostatic processes, such as urea retention, acid-base regulation and ionoregulation, and/or an osmoregulatory compromise due to increased functional gill surface area. Overall, the results provide a comprehensive picture of the physiological responses to a severe degree of hypoxia in an ancient fish species.
authors.affiliation: Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada; 2Bamfield Marine Sciences Centre, Bamfield, British Columbia V0R 1B0, Canada; 3Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada, and Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida 33149.
authors.forename: Alex M
authors.initials: AM
authors.lastname: Zimmer
authors.forename: Chris M
authors.initials: CM
authors.lastname: Wood
mesh_terms: D000693:Anaerobiosis; D000818:Animals; D006863:Hydrogen-Ion Concentration; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D048250:Squalus; D048251:Squalus acanthias / Q000502:physiology*; D014508:Urea / Q000378:metabolism*; D014882:Water-Electrolyte Balance
chemical_list: D014508:Urea; D010100:Oxygen