Oxygen Consumption in the Spontaneously Hypertensive Rat

Summary Oxygen utilization was found to be elevated in SH rats as compared to control animals, and the difference was statistically significant at ambient temperatures above 25°. Corresponding elevations in rectal temperature were noted, and it was concluded that the enhanced metabolic response was related to the relative inability of the hypertensive rat to prevent rectal temperature elevation during heat stress. It was not clear as to whether the increase in O2 uptake was a causal factor or resulted from body temperature elevation due to defective heat loss by the SH rat. Propranolol induced a significant reduction in oxygen usage of both SHR and WKY groups at Ta 30° but not at 21° indicating an adrenergic influence on metabolic rate during acute heat stress which was absent during cooler exposures. Serum T4 levels of SH rats were not significantly different from control values whereas T3 levels were elevated (26%) indicating normal or slightly increased thyroid activity. In comparison, TSH levels were elevated fourfold indicating a markedly abnormal thyroid response to this hormone.