CHRONIC EXERCISE DECREASES ADRENERGIC AGONIST-INDUCED VASOCONSTRICTION IN SPONTANEOUSLY HYPERTENSIVE RATS

This study was conducted to investigate the effects of chronic exercis e on adrenergic agonist-induced vascular responses in spontaneously hy pertensive rats (SHR). Four-week-old male SHR and Wistar-Kyoto rats we re divided into control and trained groups. The trained groups ran on a drum exerciser at 70% of peak oxygen consumption for 60 min/day 5 da ys/wk for 10 wk. Resting systolic blood pressure and heart rate were m easured by a tail-cuff method, and changes in these parameters were co nsidered as indexes of effective training. At the end of experiments, thoracic aortas and carotid arteries were isolated. Vasoconstricting r esponses to norepinephrine (NE) or phenylephrine (PHE) were studied. T o clarify the role of endothelium-derived nitric oxide (EDNO) in the a lteration of NE-induced vasoconstriction after chronic exercise, we me asured the changes in vasoconstricting responses to NE (10(-8) M) afte r treatment with N-omega-nitro-L-arginine. Vasorelaxing responses to P HE or clonidine were also studied. Our results showed that 1) vasocons tricting responses to NE or PHE in the endothelium-intact thoracic aor ta were reduced, whereas PHE- or clonidine-induced EDNO release was en hanced by exercise training, and 2) the latter could be eliminated by N-omega-nitro-L-arginine. Therefore, training may decrease adrenergic agent-induced vasoconstricting responses by increasing their stimulate d EDNO release in hypertensive and normotensive rats.