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1 Department of Biology, University of Ottawa, K1N 6N5; and 2 Department of Biology, Carleton University, Ottawa, Ontario K1S 5B6, Canada
The blood
transit time through the gills of rainbow trout (Oncorhynchus
mykiss) was modified by manipulation of cardiac output (
b).
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
b was
elevated (by 13.3 ± 2.4 ml · min
1 · kg
1) by
intravascular saline injection or reduced (by 10.8 ± 1.8 ml · min
1 · kg
1) by removal
of plasma. The arterial partial pressure of CO2
(PaCO2; an index of CO2 excretion
efficiency) was increased with elevated
b and was decreased with
reduced
b such that the changes in PaCO2
exhibited a significant positive sigmoidal relationship with the
changes in
b (r2 =0.75; P < 0.05). In contrast, there was no significant relationship between
changes in the arterial partial pressure of O2
(PaO2; an index of O2 uptake efficiency)
and changes in
b (r2 = 0.07;
P > 0.05). The intravenous administration of carbonic anhydrase (CA; 10 mg/kg) before vascular volume loading eliminated the
increase in PaCO2 with increased
b that was
observed in control fish.
diffusion; perfusion; oxygen uptake; transit time; cardiac output; gill
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