AJP - Regulatory, Integrative and Comparative Physiology, Vol 249, Issue 2 246-R254, Copyright © 1985 by American Physiological Society
Isolated perfused head of rainbow trout. I. Gas transfer, acid-base balance, and hemodynamics
S. F. Perry, C. E. Booth and D. G. McDonald
Branchial gas transfer, acid-base balance, and hemodynamics were critically
evaluated and compared in Ringer-perfused and blood-perfused heads of
rainbow trout. Blood perfusion stimulated O2 uptake and CO2 excretion
across the gills to values more representative of intact fish. The
stimulatory effect of blood on gas transfer was due to increased O2
carrying capacity (O2 uptake) and the presence of erythrocytic carbonic
anhydrase (CO2 excretion). Adding carbonic anhydrase to Ringer enhanced CO2
excretion in a manner similar to blood. During Ringer perfusion,
arteriovenous pH gradients were abnormal (arterial pH less than venous pH).
Perfusion with blood or addition of carbonic anhydrase to Ringer reversed
the pH gradients to typical in vivo levels. Branchial vascular resistance
to flow was abnormally high in both Ringer- and blood-perfused
preparations, primarily as a result of low dorsal aortic pressure. Input
pressure increased during blood perfusion and was similar to ventral aortic
pressure in vivo. Perfusion with Ringer may have caused irreversible
deterioration of gill function as indicated by decreased arterial Po2 and
O2 extraction effectiveness after a rapid switch from Ringer to blood
perfusion. The results are discussed with reference to the suitability of
perfused trout head preparations for studying gill gas transfer, acid-base
balance, and hemodynamics. Comparisons are made between the perfused head
preparation and intact fish as well as with other types of perfused gill
preparations.
