EFFECTS OF ACUTE AND CHRONIC EXERCISE ON VASOCONSTRICTOR RESPONSIVENESS OF RAT AORTA

Abstract

1782 It has been hypothesized that the reduction in blood pressure associated with exercise training is a result of a sustained postexertional vascular alteration following single bouts of exercise. The purpose of this study was to determine whether a decrease in vascular sensitivity to vasoconstrictor agonists occurs following a single bout of exercise and whether this vascular alteration is sustained through various periods of exercise training. Vasoconstrictor responses to KCl (10-100mM), phenylephrine (PE, 10−8 - 10−4 M), and arginine vasopressin (AVP, 10−9 - 10−5 M) were determined on abdominal aortic rings in vitro in sedentary (SED) rats and immediately after a single bout of treadmill exercise (30 m/min for one hour) in post-exercise (POST-EX) rats. Neither vascular sensitivity nor tension development to KCl, PE and AVP were diminished after exercise. To determine the duration of exercise training necessary to induce changes in vascular sensitivity to adrenergic stimulation, vascular responses to norepinephrine (NE, 10−9 - 10−4 M) were determined immediately after exercise in POST-EX rats and 24 hours after the last exercise bout in rats exercised for 1 DAY, 1 WK, 2 WK, 4 WK, and 10 WK at 30m/min, 60 m/min, 5 days/wk. Sensitivity to NE was diminished following 10 WK of training. This diminished vascular sensitivity to NE was abolished with the removal of the endothelial cell layer. These data indicate that a single bout of exercise does not diminish arterial responsiveness to vasoconstrictor agonists, but sensitivity to NE is diminished after 4 to 10 weeks of moderate-intensity exercise training. This adaptation appears to be mediated through an endothelium-dependent mechanism.