Blood acid-base status of an awake heterothermic rodent, Spermophilus tereticaudus

The desert ground squirrel Spermophilus tereticaudus is shown to show both reptilian style alphastat regulation and the pH-stat regulation typical of mammalian hibernation, depending upon the range of body temperature and the state of vigilance. Temperature corrected arterial pH and PCO2 of torpid squirrels (Tb 11-28 degrees C) were independent of Tb and about equal to euthermic values at 37 degrees C. Torpid squirrels show a progressive respiratory acidosis as Tb is lowered. In awake heterothermic squirrels (Tb 30-42.5 degrees C), blood acid-base status is like that of many ectothermic vertebrates: from 30 to 40 degrees C delta pHa/delta Tb was -0.0121, delta PaCO2/delta Tb was 1.057 and [HCO3-] remained about constant. Arterial blood from awake heterothermic squirrels measured at standard temperature (37 degrees C) showed no significant change with Tb, similar to blood undergoing anaerobic temperature changes in vitro. In vitro, the delta pH/delta T of blood of constant CCO2 was -0.014. Constant blood pH with change in Tb is thus not a general feature of mammalian acid-base regulation but appears in this species to be a feature of the respiratory and metabolic poise of torpor.