Effects of Experimental Hypertension and of Aging on the Spontaneous Running Activity of Rats

¹ From the Department of Physiology, Harvard Medical School, Boston, Massachusetts

Under conditions of constant temperature at 25°C and controlled illumination, the spontaneous running activities of separate groups of experimentally hypertensive rats were measured at graded periods of time after bilateral kidney encapsulation. The activity of hypertensive rats was greater than that of controls from 3–8 weeks after kidney encapsulation; i.e., during the time blood pressure was increasing. When blood pressure became maximally elevated (8–9 weeks after kidney encapsulation), activity of hypertensive rats decreased to that of control rats and thereafter the activities of both groups decreased in the same fashion with increasing age. Under these conditions hypertensive disease did not impose a limitation on spontaneous activity despite the increased work load of the heart and the elevated mean blood pressure. Comparable results were also observed when hypertensive and normal rats were kept continuously in activity cages. Unrestricted activity did not affect either the time course of development or the severity of the elevated blood pressure.