Influence of temperature on the optimal hematocrit of the bullfrog (Rana catesbeiana)

Summary The influence of temperature on blood viscosity and consequently on the potential for oxygen transport by blood was determined using a controlled flow, variable pressure tube viscometer, and blood from adult bullfrogs. Blood viscosity was determined as a function of hematocrit and temperature, and oxygen capacity was determined as a function of hematocrit. These data were used to describe 1) the potential for oxygen transport in the tube viscometer, and 2) the relation between the optimal hematocrit, the hematocrit which provided the greates oxygen transport, and temperature. The optimal hematocrit increased at a rate of 0.237% per °C increase in temperature. This value is close to the rate of change inin vivo hematocrit of 0.246 and 0.240% per °C increase in body temperature (T_b) observed in winter bullforgs acclimated to 5 and 20°C, respectively. During the summer the hematocrit ratio showed no consistent relation to T_b. These results suggest that in bullfrogs the cardiovascular adjustments to change in T_b involve the optimal hematocrit in winter, but not in summer.