ACIDOSIS AND METABOLIC-RATE IN GOLDEN-MANTLED GROUND-SQUIRRELS (SPERMOPHILUS-LATERALIS)

In this study, three series of experiments were conducted on euthermic, anesthetized, artificially ventilated golden mantled ground squirrels (Spermophilus lateralis), each of which altered pHa in a different fashion. In Series I, animals were randomly hypo- or hyper-ventilated. On average, pHa changed from 7.13 to 7.59, Pa(CO2) from 59.2 to 23.6 Torr, and Pa(O2) from 45.8 to 57.2 Torr between the two conditions, respectively. V(O2) showed a significant positive correlation with pHa (r = + 0.84) as well as Pa(O2) (r = + 0.60). In Series II, respiratory acidosis was produced by pump-ventilating animals with up to 10% inspired CO2 to reduce pHa to within the range 7.40 to 7.20. On average, pHa was reduced to 7.30, Pa(O2) to 50.1 Torr and Pa(CO2) WaS increased to 56.7 Torr. As in Series I, there was a significant positive correlation between V(O2) and pHa (r = + 0.78) and between V(O2), and Pa(O2) (r = + 0.7 1). In Series III, metabolic acidosis was produced by infusing lactic or acetic acid intravenously for 20 to 30 min. This reduced pHa from 7.56 to 7.32, Pa(O2) from 70.2 to 58.9 Torr, and elevated Pa(CO2) from 26.9 to 37.9 Torr (P< 0.05 in all cases). Contrary to Series I and II, V(O2) increased with a decline in pHa (r = - 0.65, P< 0.05) and Pa(O2) (r = - 0.55, P < 0.05). Thus, despite a significant decline in pHa and Pa(O2) and an elevation of Pa(CO2) during all three series, V(O2) changed in opposite directions during respiratory and metabolic acidosis. We conclude that whatever the mechanism involved, hypoventilation during the early stages of entrance into hibernation can contribute to the fall in metabolic rate.