DECREASED VASCULAR SENSITIVITY AFTER ACUTE EXERCISE AND CHRONIC EXERCISE TRAINING IN RAT THORACIC AORTA

The effects of acute and chronic physical exercise on the sensitivity of isolated aorta to norepinephrine were investigated. After chronic e xercise, the EC(50) values for norepinephrine increased 3.1-fold and 2 .3-fold in endothelium-intact and in endothelium-denuded aorta, respec tively. The attenuated sensitivity of aorta to norepinephrine after ch ronic exercise was still evident in endothelium-denuded aorta, but to a lesser extent than in endothelium-intact aorta. After acute exercise , in control rats, the EC(50) values increased 7.8-fold and 5.4-fold i n endothelium-intact and endothelium-denuded aorta, respectively. The attenuated sensitivity of aorta to norepinephrine after an acute exerc ise was still evident in endothelium-denuded aorta. In trained rats, t he EC(50) values increased 2.3-fold and 2.6-fold in endothelium-intact and endothelium-denuded aorta, respectively. Thus, acute exercise was less effective in trained than in control rats. No significant differ ence in 60 mM KCl-induced tension between control and trained rats was observed with or without endothelium after acute and chronic exercise . The results suggest that levels of endothelium-dependent releasing f actor may increase in response to norepinephrine after acute and chron ic exercise. In addition, the attenuated sensitivity of aorta to norep inephrine after acute and chronic exercise may also result from the ch ange(s) in the receptor sites. However, the degree of desensitization caused by acute exercise was less in the rats adapted to chronic exerc ise than in the sedentary control rats.