Cardiovascular and metabolic responses to temperature in Coluber constrictor

The cardiovascular adjustments associated with elevated metabolic demand caused by rising body temperature were investigated in Coluber constrictor. From 16 to 35 degrees C, O2 consumption increased roughly ninefold. Systemic blood flow, determined by the Fick method, increased approximately 4.5-fold and arteriovenous O2 difference increased approximately 2-fold. Heart rate steadily increased over the temperature range examined. At the cooler temperatures stroke volume also increased but, above approximately 25 degrees C, stroke volume declined with rising temperature. The changes in stroke volume may result from the direct effect of temperature on myocardial contractility. The thermal dependence of blood convection requirement in C. constrictor is similar to changes in air convection requirement determined in a previous study. Consequently the minute ventilation-to-perfusion ratio appears to be independent of temperature, at least from 20 to 35 degrees C. Systemic arterial blood pressure increases with rising body temperature due to the rise in cardiac output, whereas vascular resistance declines. Blood pressure in snakes disturbed by the investigator is roughly two times higher than in resting animals at all temperatures studied. This marked change in blood pressure suggests an "alarm reaction" mediated by the sympathetic nervous system.