POSTEXERCISE LACTATE METABOLISM - A COMPARATIVE REVIEW OF SITES, PATHWAYS, AND REGULATION

Most vertebrates utilize supplemental lactate production to support th e energetic demands of vigorous, brief exercise. Despite similar patte rns of accumulation, there appears to be a trichotomy with regards to lactate processing post-exercise. Most fish retain most of their lacta te intramuscularly, using it for in situ glycogen replenishment. Recen t evaluation of fish muscle concludes that pyruvate kinase reversal is a probable gluconeogenic pathway. Amphibians and reptiles also utiliz e lactate as a muscle glyconeogenic substrate, but lactate is not sequ estered post-exercise. None of these groups utilize hepatic gluconeoge nesis to any significant extent post-exercise, and muscle glucose upta ke is limited. Lactate oxidation plays a major role post-exercise in m ammals, with hepatic and muscular gluco- and glyconeogenesis contribut ing to a lesser extent. Glucocorticoids may regulate lactate release f rom fish muscle, although catecholamines may influence glyconeogenesis in reptile muscle. Insulin affects lactate metabolism indirectly thro ugh its effects on muscle glucose metabolism.