SHORT-TERM EXERCISE TRAINING ENHANCES REFLEX CHOLINERGIC NITRIC OXIDE-DEPENDENT CORONARY VASODILATION IN CONSCIOUS DOGS

The effects of exercise training on the coronary vasodilation followin g activation of the Bezold-Jarisch reflex were examined in conscious d ogs. Mongrel dogs were chronically instrumented using sterile techniqu es for measurements of systemic hemodynamics and left circumflex coron ary blood flow (CBF). With the heart rate controlled (150 bpm), veratr ine (0.5 to 20 mu g/kg) caused dose-dependent increases in CBF; eg, 5 mu g/kg of veratrine increased CBF by 61+/-6% from 31+/-1.3 mL/min (P< .05). After exercise training, the dose-response curve of CBF in respo nse to veratrine was shifted to the left: eg. 5 mu g/kg of veratrine i ncreased CBF by 101+/-12% (P<.05 compared with control) from 34+/-2.3 mL/min. The enhanced coronary vasodilation was blunted by nitro-L-argi nine (NLA, 35 mg/kg). In anesthetized dogs after exercise training, el ectrical stimulation of the left vagus nerve caused greater increases in CBF, and NLA inhibited increases in CBF. Acetylcholine, norepinephr ine, angiotensin II, and bradykinin caused greater increases in NO2- p roduction in coronary microvessels from exercise-trained dogs compared with those from normal dogs. Our results indicate that the coronary v asodilation following activation of the Bezold-Jarisch reflex is enhan ced in conscious dogs after exercise training. Since electrical stimul ation of the vagus nerve caused greater coronary vasodilation and sinc e the agonists resulted in greater increases in NO production in coron ary microvessels from exercise-trained dogs! the mechanism responsible for the enhanced coronary vasodilation following activation of the Be zold-Jarisch reflex is most likely due to the increased release of NO from the endothelial cells.