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The influence of exercise training on the resting caudal arterial blood pressures (RBP) of hypertensive rats is unclear despite numerous investigations by different investigators. To determine whether RBP values were influenced by the intensity and the initial age of the animal at the time of training, several studies were undertaken that involved more than 100 rats. When male and female rats were endurance trained for 24 wk at an O2 consumption in excess of 75% of their maximum (Vo2 max), RBP results from nontrained (NT) or trained (T) animals were not significantly different even though at several time periods the T animals had higher resting pressures. However, when exercising rats at an intensity level representing 40-60% of their Vo2 max, the T groups had consistently lower RBP than their NT controls during the majority of the experimental time periods. In addition exercising young (2-3 wk old) hypertensive-prone rats at a moderate intensity was associated with lower RBP within 4-6 wk after the initiation of training; however, exercise training could not normalize RBP. Reduced dosages (85% of normal) of antihypertensive medication, when combined with moderate training, was also associated with lower and "normal" RBP in male but not female rats. We conclude that moderate exercise at an early age when combined with subnormal dosages of antihypertensive medication holds promise for the normalization of RBP in male hypertensive rats of a genetic origin.

To determine whether the lowered resting blood pressure values in hypertensive rats were associated with changes in vascular reactivity and/or contractility, helical strips were obtained from different arteries from exercise-trained (running and swimming) hypertensive rats and from running normotensive rats. Each subgroup contained nontrained controls for comparison. Changes in muscle aerobic enzymes, maximum O2 consumption, and body weight indicated that a training effect had occurred. When norepinephrine was added in a dose-response manner to the testing chamber containing helical strips from either the descending aorta, femoral artery, or renal artery, there were no significant differences in reactivity (the negative log dose-response curve) attributable to the training of hypertensive or normotensive groups. However, the trained hypertensive rats exhibited a trend for lower contractility values (dyn/mm2) in some but not all of the strips tested. From these results, we concluded that the lowered resting blood pressures associated with exercise training of hypertensive rats could not be explained by changes in vascular reactivity of their arterial strips.

To determine whether voluntary exercise would lower resting blood pressure in spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SP-SHR), two separate but interrelated investigations were undertaken. The studies were initiated when the animals were 28-35 days of age and after they were assigned to either activity or sedentary cages. The activity cages were connected to transducers and recorders that allowed the monitoring and calculation of frequency, duration, and running speed. The SHR group ran 3-7 km/day intermittently for 12 wk at high speeds (48-68 m/min), which resulted in heart rates in excess of 500 beats/min. When the SHR exercised, they seldom exceeded 33 revolutions/bout (37 m) with the majority being less than 22 revolutions/bout. This type of exercise training significantly lowered, but did not normalize, resting blood pressure by approximately 20 mmHg [nontrained (NT) = 185 +/- 5; trained (T) = 163 +/- 5 mmHg] while increasing maximum O2 consumption (VO2max) (NT = 78 +/- 2.6; T = 95 +/- 2.2 ml X min-1 X kg-1) and endurance run time (NT = 62 +/- 9.0; T = 286 +/- 15.0 min), respectively. Although SP-SHR exhibited comparable patterns of voluntary activity, the effects were not similar. First, after approximately 5 wk of consuming a special Japanese rat chow and a 1% NaCl drinking solution, cerebrovascular lesions occurred and deaths ultimately resulted in both exercising and sedentary groups. Second, although there was statistical evidence for a training effect (higher VO2max, longer VO2 test run times), voluntary exercise had no advantage in either male or female runners in lowering resting blood pressures or in improving their life-spans. Whereas voluntary activity wheel exercise or moderate forced treadmill exercise will lower resting blood pressures in young SHR populations, similar generalizations cannot be made with young SP-SHR rats.

The single and combined influences of exercise training, chemical sympathectomy (SYMX), and surgical adrenal demedullation (D) were examined in four separate spontaneously hypertensive rat (SHR) groups. SYMX was accomplished by subcutaneous injections of antinerve growth factor (ANGF) over a 5-day period after birth followed by 20 separate injections of guanethidine sulfate during a 27-day period. Measurements of urine, plasma, or tissue levels of catecholamines indicated that these experimental procedures were effective. The animals were exercise trained (T) for 10 wk or longer at 40-60% of their VO2max capacity, and all T groups exhibited longer run times or higher muscle cytochrome oxidase activity; however, only the SHR + T subgroup had a significantly higher VO2max value than its control (NT). Training lowered resting systolic blood pressure (SBP) in the SHR subgroup but normalization of SBP occurred only with SYMX. Interestingly, only the SYMX + T subgroup with intact adrenal glands also had lower SBP values than the NT. The SHR + T and SYMX + T subgroups but not the SYMX + D + T had less cardiac acceleration after ip injections of atropine than their controls. Heavier heart weights were observed only in the SHR + T subgroup; SYMX was associated with lighter heart weights regardless of whether the rats had been T or D. These collective findings demonstrated again the importance of the sympathetic nervous system to an exercise response, suggesting that an intact adrenal medulla was essential for SHR groups to achieve many of the adaptations associated with training.