title: Sensitivity of CO2 excretion to blood flow changes in trout is determined by carbonic anhydrase availability.
abstract: The blood transit time through the gills of rainbow trout (Oncorhynchus mykiss) was modified by manipulation of cardiac output (Vb). The experiments tested the hypothesis that efficiency of CO2 excretion is sensitive to changes in blood flow owing to chemical equilibrium limitations. An extracorporeal blood shunt was used to continuously monitor blood gases in fish in which Vb was elevated (by 13.3 +/- 2.4 ml x min(-1) x kg(-1)) by intravascular saline injection or reduced (by 10.8 +/- 1.8 ml x min(-1) x kg(-1)) by removal of plasma. The arterial partial pressure of CO2 (Pa(CO2); an index of CO2 excretion efficiency) was increased with elevated Vb and was decreased with reduced Vb such that the changes in Pa(CO2) exhibited a significant positive sigmoidal relationship with the changes in Vb (r2 =0.75; P < 0.05). In contrast, there was no significant relationship between changes in the arterial partial pressure of O2 (Pa(O2); an index of O2 uptake efficiency) and changes in Vb (r2 = 0.07; P > 0.05). The intravenous administration of carbonic anhydrase (CA; 10 mg/kg) before vascular volume loading eliminated the increase in Pa(CO2) with increased Vb that was observed in control fish.
authors.affiliation: Department of Biology, University of Ottawa, K1N 6N5, Ontario K1S 5B6, Canada.
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Desforges
authors.forename: Stuart S
authors.initials: SS
authors.lastname: Harman
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Gilmour
authors.forename: Steve F
authors.initials: SF
authors.lastname: Perry
mesh_terms: D000818:Animals; D001810:Blood Volume / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism*; D002256:Carbonic Anhydrases / Q000378:metabolism* / Q000494:pharmacology; D002302:Cardiac Output / Q000502:physiology; D004058:Diffusion; D005260:Female; D005880:Gills / Q000098:blood supply* / Q000502:physiology; D008297:Male; D017686:Oncorhynchus mykiss / Q000502:physiology*; D010100:Oxygen / Q000493:pharmacokinetics; D010313:Partial Pressure; D010949:Plasma; D011659:Pulmonary Gas Exchange / Q000187:drug effects / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D002256:Carbonic Anhydrases; D010100:Oxygen