title: The mechanisms of acid-base and ionoregulation in the freshwater rainbow trout during environmental hyperoxia and subsequent normoxia. I. Extra- and intracellular acid-base status.
abstract: The extracellular acid-base status of the freshwater rainbow trout (Salmo gairdneri) was continuously monitored during 24 h normoxia (PIO2 = 120-150 torr; control), 72 h hyperoxia (PIO2 = 500-600 torr) and 24 h return to normoxia. Hyperoxia induced a marked respiratory acidosis (delta pHe = -0.23 unit) due to a 3-fold elevation in arterial CO2 tension which was completely compensated over 72 h by a comparable rise in plasma bicarbonate, reflecting effective removal of acidic equivalents from the ECF. Upon return to normoxia, arterial CO2 tension rapidly returned to normal against a background of high plasma bicarbonate, provoking a metabolic alkalosis which was largely compensated by 24 h. This effective restoration of acidic equivalents in the ECF occurred more rapidly than the original removal. Intracellular acid-base status was measured during normoxia and after 72 h hyperoxia using the steady state distribution of 14C-DMO. The rate of 14C-DMO excretion was 0.479 +/- 0.048 (% DMO lost per hour) during normoxia, and significantly decreased with hyperoxia. A considerable overestimate of mean whole body pHi would have resulted had this not been taken into account. Whole body and white expaxial muscle were similar with a pHe - pHi gradient of ca. 0.5 during normoxia, and underwent identical changes during hyperoxia. Intracellular pH was completely compensated by 72 h hyperoxia as intracellular bicarbonate increased 4-fold. The overall net removal of acidic equivalents from the ICFV was approximately one half that from the ECFV , but pHe regulation did not occur at the expense of pHi regulation. The ultimate restoration of both pHe and pHi during hyperoxia must have occurred via kidney or gills.
mesh_terms: D000136:Acid-Base Equilibrium / Q000187:drug effects; D000818:Animals; D001639:Bicarbonates / Q000097:blood; D001826:Body Fluids / Q000378:metabolism*; D002245:Carbon Dioxide / Q000097:blood; D004114:Dimethadione / Q000378:metabolism / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism*; D005260:Female; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000378:metabolism*; D008297:Male; D009132:Muscles / Q000378:metabolism; D010100:Oxygen / Q000097:blood / Q000502:physiology*; D012487:Salmonidae / Q000378:metabolism*; D014337:Trout / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D002245:Carbon Dioxide; D004114:Dimethadione; D010100:Oxygen