Effect of ambient temperature on cardiovascular parameters in rats and mice: a comparative approach

Ambient air temperatures (T-a) of <6 degrees C or >9degreesC have been shown to induce large changes in arterial blood pressure and heart rate in homeotherms. The present study was designed to investigate whether small incremental changes in Ta, such as those found in typical laboratory settings, would have an impact on blood pressure and other cardiovascular parameters in mice and rats. We predicted that small decreases in Ta would impact the cardiovascular parameters of mice more than rats due to the increased thermogenic demands resulting from a greater surface area-to-volume ratio in mice relative to rats. Cardiovascular parameters were measured with radiotelemetry in mice and rats that were housed in temperature-controlled environments. The animals were exposed to different Ta every 72 h, beginning at 30degreesC and incrementally decreasing by 4degreesC at each time interval to 18degreesC and then incrementally increasing back up to 30degreesC. As Ta decreased, mean blood pressure, heart rate, and pulse pressure increased significantly for both mice (1.6 mmHg/degreesC, 14.4 beats.min(-1).C-degrees(-1), and 0.8 mmHg/degreesC, respectively) and rats (1.2 mmHg/degreesC, 8.1 beats.min(-1) .degreesC(-1), and 0.8 mmHg/degreesC, respectively). Thus small changes in Ta significantly impact the cardiovascular parameters of both rats and mice, with mice demonstrating a greater sensitivity to these Ta changes.