EXERCISE TRAINING AND INCIDENCE OF CEREBROVASCULAR LESIONS IN STROKE-PRONE SPONTANEOUSLY HYPERTENSIVE RATS

To assess the effects of moderate exercise [40-70% maximal oxygen uptake (V̇O(2 max))] on resting blood pressures, the presence of cerebrovascular lesions, and the life spans of stroke-prone hypertensive rats, nontrained and trained male and female rats were assigned to two experimental groups. The first (n = 48) were exercise trained after 38 days of age, whereas the second (n = 44) initiated exercise training when the animals were 134 days of age. To facilitate cerebrovascular lesions, the sodium concentrations in the rat chow and in the drinking solutions were increased. Symptoms utilized to denote the presence of cerebrovascular lesions were irritability, hyperresponsiveness, ataxia, lethargy, unwillingness to run, and combinations thereof. All brains were removed immediately after death, fixed, and evaluated grossly and microscopically for lesions. In the study with the younger animals, training was associated with a 7-9% increase in V̇O(2 max) that was statistically significant only in animals with no histological evidence of cerebrovascular lesions. For the older animals, a significant 5-8% increase in V̇O(2 max) was noted for animals with or without lesions. After 42 days of training for both groups resting blood pressures for the trained groups with histological lesions were significantly lower. However, this trend did not continue, and the older trained rats appeared to have strokes earlier and to die sooner than their nontrained controls. Although 83% of the older animals had subjective evidence for a stroke before they died, the percentage of animals with lesions ranged from 42 to 58%, with the trained groups having higher percentages. From these experiments we concluced that moderate exercise, although partially attenuating the rise in pressure associated with time, did not significantly reduce the incidence of cerebrovascular lesions or prolong the life spans of the trained animals. Because the presence of the sympathetic nervous system has a protective effect against the incidence of strokes in stroke-prone hypertensive populations, we speculate that chronic exercise increases the vulnerability of trained rats because of a reduction in their resting 'sympathetic tone'.