Cardiovascular and metabolic responses of hypertensive and normotensive rats to one week of cold exposure

Challenges to energy homeostasis, such as cold exposure, can have consequences for both metabolic and cardiovascular functioning. We hypothesized that 1-wk cold exposure (4 degrees C) would produce concurrent increases in metabolic rate (VO2; indirect calorimetry), heart rate (HR), and mean arterial blood pressure (MAP) measured by telemetry. In the initial hours of change in ambient temperature (T-a), both spontaneously hypertensive rats (SHRs) and normotensive Sprague-Dawley rats showed rapid increases (in cold) or decreases (in rewarming) of VO2, HR, and MAP, although the initial changes in MAP and HR were more exaggerated in SHRs. Throughout cold exposure, HR, VO2, food intake, and locomotor activity remained elevated but MAP decreased in both strains, particularly in the SHR. During rewarming, all measures normalized quickly in both strains except MAP, which fell below baseline (hypotension) for the first few days. The results indicate that variations of T-a produce rapid changes in a suite of cardiovascular and behavioral responses that have many similarities in hypertensive and normotensive strains of rats. The findings are consistent with the general concept that the cardiovascular responses to cold exposure in rats are closely related to and perhaps a secondary consequence of the mechanisms responsible for increasing heat production.