Effect of deep hypoxia on acid-base balance in trout: role of ion transfer processes.

Continuous recordings were made of pH, Po2, and Pco2 of arterial blood in an extracorporeal circulation during a 20-min period of deep hypoxia (inspired Po2 = 40 Torr) and subsequent normoxia in rainbow trout. Blood concentrations of lactate, Na+, K+, and Cl- and net fluxes of electrolytes across gills and kidney were also continuously monitored. Deep hypoxia induced a short respiratory alkalosis followed by a marked metabolic acidosis. The acidification is biphasic in nature. The first rapid phase of acidification is not related to lactic acid production. On the other hand, the second phase of acidification is associated with lactic acid diffusion into the blood. However, a considerable proportion of the lactate ions is balanced by Na+ ions coming from a shift in the distribution of this cation between intra- and extracellular compartments. Most of the H+ ions formed from the dissociation of lactic acid are buffered in the intracellular space. The acidification period is also characterized by a very small increase in plasma Cl- content, much less than that of Na+, and by the apparent accumulation of an unknown anion in the blood. Recovery from hypoxia is associated with a pH readjustment, a large and identical decline of blood Na+ and Cl- contents without modification of the concentrations of K+, lactate, and the unknown anion. During this period the branchial ionic exchanges are slightly stimulated, but in the acid-base regulation as a whole, the branchial regulatory processes only play a minor part, the ionic movements being mainly performed by transfer between intra- and extracellular spaces.(ABSTRACT TRUNCATED AT 250 WORDS)