A NEW FUNCTION FOR LACTATE IN THE TOAD BUFO-MARINUS

In the amphibian Bufo marinus, progressive hypoxia below a critical PO 2 elicits a transient 50% increase in O-2, consumption that coincides with the onset of lactate formation. The present study was designed to test the hypothesis that lactate causes the observed rise in metaboli c rate. Arterial bolus infusions of pH-neutral sodium lactate solution s (4 mmol/kg body wt) in toads maintained under hypoxia actually elici t a similar increase in metabolic rate. The application of adrenergic antagonists (bretylium tosylate, phentolamine, propranolol, and reserp ine) inhibits this response, suggesting that catecholamines are involv ed. Moreover, animals injected with lactate move to a cooler environme nt (behavioral hypothermia), a behavioral response that is beneficial during hypoxia. We hypothesize that, in accordance with Cannon's conce pt of an emergency response, lactate may function as an alarm signal d uring hypoxia. However, the signal function of lactate is observed in animals both under hypoxia and under normoxia and should thus be consi dered in future studies whenever elevated lactate levels are present, e.g., during and after exercise.