Acute and chronic temperature effects on cardiovascular regulation in the red-eared slider (Trachemys scripta)
Acute and chronic changes in ambient temperature alter several aspects of reptilian physiology. We investigated the effects of each type of temperature change on reptilian cardiovascular regulation in red-eared slider turtles (Trachemys scripta), a species known to experience marked seasonal changes in ambient temperature. Turtles were instrumented with occlusive catheters in the femoral artery and vein. Following an acclimation period of 10 days at 13 °C (131), cardiovascular responses to adrenaline, and the cardiac limb of the baroreflex were quantified. Ambient temperature was then reduced 1 °C day−1 until 3 °C was reached (31). Turtles were maintained at this temperature for 1-week before cardiovascular responses were reassessed. Turtles were then gradually (1 °C day−1) returned to an ambient temperature of 13 °C, (132). After a 1-week re-acclimation period, cardiovascular responses were again determined. Finally, 1-week post-pharmacological manipulation of turtles in the 132 treatment, ambient temperature was reduced to 3 °C over 24 h (32), and cardiovascular responses were again assessed. Temperature reduction from 131 to 31 decreased mean arterial blood pressure (Pm) and heart rate (fH) by ~38 and ~63 %, respectively. Acute temperature reduction, from 132 to 32, decreased fH similarly, ~66 %; however, while Pm decreased ~28 %, this was not significantly different than Pm at 132. The adrenaline injections increased fH ranging from 90 to 170 % at 13 °C which was a greater change than that observed at 3 °C ranging from a 40 to 70 % increase. The increase in Pm at the lowest dose of adrenaline did not differ across the temperature treatment groups. The operational point (set-point) Pm of the baroreflex was decreased similarly by both methods of temperature reduction (31 or 32). Further, a hypertensive cardiac baroreflex was absent in the majority of the animals studied independent of temperature. Baroreflex gain and normalized gain based on individual estimates of the relationship were decreased by temperature reduction similarly. Collectively, the data suggest that red-eared slider turtles modulate (down-regulate) some cardiovascular control mechanisms during reduced ambient temperature.