Effects of norepinephrine infusion and exercise on blood pressure in rats

Two experiments were conducted to test the hypotheses that norepinephrine (NE) infusion would increase blood pressure and wheel running activity level, and, secondly, that voluntary exercise would lower NE-induced increases in blood pressure. NE-bitartrate was infused into male Sprague-Dawley rats using an implanted osmotic pump (3.75 micrograms/kg/min in 0.9% saline). Control rats received the vehicle solution. Systolic blood pressure was measured by the tail-cuff method. Voluntary wheel running activity expressed as wheel revolutions per 24 hr was measured on the 5th, 9th, and 13th day. Blood pressure on the 13th day and wheel running activity on the 9th day were significantly higher in NE-infused rats. The NE content of heart tissue was not altered, but urinary excretion of NE and epinephrine was increased in the NE-infused animals. Food intake, body weight gain, and kidney weight per 100 g body wt were not changed but heart weight per 100 g body wt was increased by NE infusion. Urinary total calcium excretion was higher in the NE-infused rats. Spontaneous voluntary exercise in running wheels attenuated increases of blood pressure in NE-infused rats. The results of the present study suggest that rats receiving exogenous NE exhibit increased blood pressure and voluntary wheel running activity. Voluntary wheel running exercise also reduces blood pressure in NE-infused rats.