Circulatory responses of Rana catesbeiana to temperature, season and previous thermal history

Abstract

1. 1. Heart rate, femoral arterial pressure, plasma volume, blood volume and hematocrit ratio were determined on unrestrained, unanesthetized winter (January–March) and summer (July- August) bullfrogs which had been acclimated ot 5 to 20°C for 2–3 weeks. 2. 2. Winter frogs exhibited an increased sensitivity of heart rate to temperature change following cold acclimation. Heart rates of warm and cold acclimated summer frogs were not significantly different at comparable body temperatures ( T b's). 3. 3. Femoral arterial pressure increased continuously with T b between 0 and 36°C in warm acclimated winter and summer frogs, but tended to remain constant (winter frogs) or increased more slowly (summer frogs) over the same range of T b's in cold acclimated animals. 4. 4. Cold acclimation had no effect on arterial capacitance measured in vitro. Arterial capacitance decreased markedly (a manifestation of increased vessel rigidity) at pressures above 30–40 mm Hg. 5. 5. While blood volume did not vary with season or acclimation temperature, plasma volume was significantly reduced in cold acclimated winter frogs. 6. 6. The hematocrit ratio increased following acclimation to cold in winter but not in summer.