Respiration and gas exchange during recovery from exercise in the Americanalligator

Low respiratory exchange ratios (R) occur in reptiles. In crocodilians they have been attributed to the loss of respiratory CO2 into the urine and to the immediate exercise-history of an animal. In this study, expired ventila tion ((V) over dot E), oxygen consumption ((V) over dot (O2)), and carbon d ioxide excretion ((V) over dot (CO2)) were measured during recovery from tr eadmill-exercise in the American alligator. Both (V) over dot (O2) and (V) over dot (CO2) decreased exponentially during recovery, but the decrease of (V) over dot (CO2) was greater than that of (V) over dot (O2). By 55 min i nto recovery R fell to 0.3 +/- 0.02 (mean +/- S.E.M). These low values of R may be partially attributable to hyperventilation that occurred during exe rcise. These data suggest that both hyperventilation during exercise and a metabolic acidosis deplete blood bicarbonate stores, contributing to a low R during recovery. We propose that the right to left cardiac shunt could fa cilitate restoration of these alkaline reserves and blood pH. (C) 2000 Publ ished by Elsevier Science B.V. All rights reserved.