The influence of exercise–handling stress on blood lactate, acid–base, and plasma glucose status of northern pike (Esox lucius L.)

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Abstract
Changes in blood lactate, pH, PCO2 [partial pressure of CO2] and plasma HCO3- and glucose were measured during recovery from exercise-handling stress in chronically cannulated northern pike (E. lucius L.). Exercise was induced by lifting pike out of water (three 30-s periods of emersion alternated with 30-s periods of water submersion), while they were inside tubular plastic chambers. Large depressions in blood pH and plasma HCO3- occurred within minutes after exercise. Initially, the acidosis was of mixed respiratory (elevated PCO2) and metabolic (H+ release from the muscle) origin. Although the respiratory acidosis was corrected in 2 h, 8 h was required to return blood pH to preexercise levels. A large accumulation of lactate anion in the blood occurred after exercise, the increase by 2 h (12.8 mmol L-1), being approximately equal to the metabolic acid load. These results conflict with previous reports on muskellunge (E. masquinongy M.), in which blood lactate elevation following exercise was small (2.5 mmol L-1) and greatly exceeded by the metabolic H+ load (7.0 mmol L-1). By 2 h after exercise the plasma glucose level of pike had increased by 8.8 mmol L-1 and the return to preexercise levels was almost complete by 12 h. Intraaarterial infusion of a large sodium lactate load elevated plasma glucose level by only 1.7 mmol L-1, indicating that postexercise hyperglycemia in pike is a response to stress and not simply a consequence of lactate removal by conversion into glucose.