Anaerobiosis and the oxygen debt in an anuran amphibian,Rana esculenta (L.)

Abstract

(1) Artificially ventilated curarised frogs consumed 23% less oxygen than animals breathing naturally but their respiratory quotient was significantly increased. Artificial ventilation maintained arterial oxygen tension at normal levels but arterial carbon dioxide tension fell significantly. When 90% of the haemoglobin was combined with carbon monoxide oxygen consumption was reduced by 40% and the respiratory quotient was increased. (2) During apnoea both normal animals and those exposed to carbon monoxide showed reductions in oxygen uptake of about 45%. Heart rate also declined by 20–40%. During apnoea respiratory quotient of both groups of animals was significantly elevated. In normal animals arterial and venous oxygen tensions fell during apnoea, arterial tensions to 20% of the ventilation value and venous oxygen tensions to a slightly higher value. Arterial oxygen content fell from 9.6 vols % to 3 vols %. Arterial carbon dioxide tensions and contents increased during the apnoea and arterial pH fell. (3) When ventilation was restored frogs consumed about 109–130 μl more oxygen in the first 10 min than in comparable periods before the apnoea. However, animals with 90% of the haemoglobin combined with carbon monoxide showed only a gradual return to the pre-apnoeic level of oxygen consumption. Heart rate, respiratory quotient and blood gas tensions returned to pre-apnoeic levels within 30 min of the resumption of artificial ventilation. The excess oxygen consumed during the first 10 min was equal to the amount of oxygen calculated to have been removed from the oxygen store of the blood during apnoea. (4) It is concluded that the blood has a function in maintaining oxygen metabolism in both ventilated and apnoeic frogs but that oxygen stores, including that of the blood, make little contribution to oxygen metabolism during apnoea and appear to be replenished immediately lung ventilation is restored.