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

Abstract

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 (VO(2); 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 VO(2), HR, and MAP, although the initial changes in MAP and HR were more exaggerated in SHRs. Throughout cold exposure, HR, VO(2), 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.

Cold-impaired cardiac performance in rats is only partially overcome by cold acclimation

“…Previous studies with CA noted enhanced catecholamine release (Depocas and Behrens, 1978), coupled with increased diurnal activity and raised f H (Chambers et al, 2000;Ishii et al, 1996), as potential initiators of hypertrophy. Preservation of developed pressure at EDV, indicative of the operating characteristic of hearts under basal contraction (Fletcher et al, 1981), suggests an adaptation to cold for the volume-dilated myocardium (Cheng and Hauton, 2008).…”

Recommendations for Blood Pressure Measurement in Humans and Experimental Animals

“…84 Similar results have also been found in several strains of rats. 85,86 The increase in food intake, metabolic rate, and BP caused by room temperature below the thermoneutral range are probably because of a generalized increase in thermogenic sympathetic nervous system activity. Because different species and strains of animals may have variable sympathetic nervous system and thermogenic responses to reductions in temperature, a low ambient room temperature may cause different effects on arterial pressure, heart rate, and other cardiovascular variables.…”

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

“…In a second set of experiments, female mice and rats of the same strain and size were implanted with telemeters as above and taken through a series of T a changes, from 30°C to 18°C and back to 30°C. In these animals (n ϭ 7 for both mice and rats), oxygen consumption was measured in addition to the cardiovascular parameters as described previously (2,28).…”

“…blood pressure; heart rate; standard deviation of the interbeat interval; radiotelemetry THE EXTERNAL ENVIRONMENT can have a substantial impact on the cardiovascular system. Exposure of humans (1,7,18,32), rats (2,3,14,20), and mice (22) to cold ambient temperature (T a ) results in elevated blood pressure and heart rate. It appears as if the tachycardia and hypertension are the indirect result of sympathetic nervous system (SNS) activation of thermoregulatory mechanisms because elevated plasma norepinephrine (NE) levels correlate with elevated blood pressure in the cold (7,14,17,32).…”