Exhaustive exercise in cannulated sea lampreys, Petromyzon marinus, resulted in a marked extracellular acidosis in the arterial blood which had both a respiratory and a metabolic component. Blood CO2 tension (PCO2) returned to control levels within an hour after exercise, but the metabolic acidosis had a somewhat longer time course and the extracellular pH (pHe) did not fully recover until the 4 h recovery sample. The magnitude and duration of the changes in both the plasma lactate concentration and the concentration of metabolic protons were very similar and the maximal proton deficit after exercise was, therefore, only 1.5 mequiv l-1. In contrast to the changes in pHe, there were no significant changes in the erythrocyte pH (pHi) following the exercise period. The regulation of pHi was apparently not adrenergically mediated, however, since addition of catecholamines to lamprey blood in vitro had no significant effect on pHi. In addition, the period of exhaustive exercise in vivo was not associated with any significant changes in the mean cellular hemoglobin concentration. The total carbon dioxide concentration in the arterial whole blood and true plasma were both significantly reduced after exercise, but the total carbon dioxide concentration within the erythrocytes was transiently increased. Finally, there was a marked decrease in the arterial PO2 immediately after exercise, which was associated with a significant reduction in the amount of oxygen bound to hemoglobin; however, within 30 min, these values had both returned to normal. The maintenance of pHi presumably contributes to the regulation of oxygen transport in lampreys and it may be particularly important during the brief period immediately after exercise when oxygen transport is clearly compromised. Although several studies have provided evidence that chloride/bicarbonate exchange limitations may exist in agnathan blood in vitro, the present results demonstrate that the characteristics of carbon dioxide transport and acid-base regulation after exercise in P. marinus are not markedly different from those in other lower vertebrates.

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