Effect of exercise on pre- and postcapillary resistance in the spontaneously hypertensive rat

Abstract

Systolic blood pressure (Ps) was measured in the intact animal, while measurements of precapillary resistance (Ra), postcapillary resistance (Rv), filtration coefficients (Kf) and capillary hydrostatic (Pc) pressure were made in the isolated perfused hindparts of normal (WKY) and spontaneously hypertensive (SHR) rats. Such measurements were made in the control state (nonexercised) and after exercise training. Systolic blood pressures in the SHR were significantly reduced in the exercise-trained animal when compared with nonexercised-SHR control animals. Exercise did not significantly reduce Ps in WKY normotensive animals. SHR precapillary resistance was significantly reduced (20-30%) as a result of exercise training. Postcapillary resistance increased in both the exercised-trained SHR (70%) and normotensive WKY (for the latter this was true only for paired sibling experiments). Since the isolated preparation cannot be influenced by neural or hormonal stimuli, the Ra decrease and Rv increase in trained SHR must result from structural modifications or intrinsic mechanisms which alter smooth muscle tone. Kf values and isogravimetric capillary pressures were not significantly different in the exercised and nonexercised WKY and SHR animals, indicating that the capillary surface area available for fluid exchange and capillary permeability to protein were similar in hypertension and normotension and not affected by exercise training. With venous pressure unchanged, the increase in postcapillary resistance, which significantly increases the Rv/Ra ratio, after training, suggests that capillary hydrostatic pressure should be elevated, promoting edema formation. Since edema is not a cardinal sign of hypertension, in the intact animal either neural or hormonal components promote hemodynamic changes which effectively compensate for an otherwise predictable increase in capillary hydrostatic pressure.