Effect of physical training on the development of hypertension in the spontaneously hypertensive rat.

The effect of chronic physical exercise on the development of hypertension was measured in spontaneously hypertensive rats (SHR) and their progenitor normotensive wistar-kyoto controls (WK). Starting 4--5 weeks after birth groups of rats were subjected to swimming exercise 1 h x day-1, 4 days x week-1 for a total period of 11 weeks. Control rats were handled daily without exercise. Both in trained SHR and WK a significant delay in increase in body weight was observed. Physical training caused a small, but significant (P less than 0.001) reduction in systolic blood pressure of SHR, whereas it did not affect blood pressure in WK. Heart rate was significantly (P less than 0.001) lower in both trained SHR and WK than in their non-trained controls. At the end of the training period the degree of training was tested by measuring muscle cytochrome oxidase activity and relative heart weight. Cytochrome oxidase activity in gastrocnemius muscle was higher in the trained animals, although the difference was only significant (P less than 0.05) for WK. Training also caused a significant (P less than 0.01) increase in the ratio heart weight to body weight in WK. Both trained and non-trained SHR have a ca. 25% higher relative heart weight than WK controls. SHR hearts did not further hypertrophy as a consequence of physical exercise. These data indicate that swim training induces a trained state in both SHR and WK. Moreover, this form of training causes a slight, but significant attenuation of the development of hypertension in SHR.