Exercise training enhances relaxation of the isolated guinea-pig saphenousartery in response to acetylcholine

The effects of exercise training were investigated on the vascular response s in the isolated guinea-pig saphenous artery. Exercising animals swam 5 da ys week(-1) for 6 weeks (60 min day(-1) for weeks 1 and 2; 75 min day(-1) f or weeks 3 and 4; 90 min day(-1) for weeks 5 and 6), while control animals were placed into shallow water for the same duration. Trained animals had s ignificantly higher ventricular:body weight ratios, increased citrate synth ase activity in the latissimus dorsi, and enhanced Na+ pump concentrations in the latissimus dorsi and gastrocnemius muscles (P < 0.05). In vitro isom etric techniques were used to measure constriction and relaxation responses of saphenous artery rings from trained and control animals. There were no significant differences in the constriction responses to KCl (50 mM) and ph enylephrine (0.3-100 mu M) in arterial rings from control versus trained an imals. Relaxation responses to acetylcholine (10 mu M; ACh-relaxation), fol lowing preconstriction with phenylephrine (10 mu M), were significantly enh anced in rings from trained animals (P < 0.05). Acetylcholine relaxed the v essels to 47 +/- 6% (control) and 18 +/- 3% (trained) of the preconstrictio n responses to phenylephrine. The nitric oxide synthase inhibitor N-G-nitro -L-arginine (L-NA; 50 mu M) significantly attenuated the ACh-relaxation in control and trained animals (P < 0.05). The effect of L-NB on the ACh-relax ation was significantly larger in trained (change in ACh-relaxation with L- NA = 29 +/- 9%) than control (14 +/- 3%) animals (P < 0.05). In conclusion, exercise training enhanced the ACh-relaxation of the isolated guinea-pig s aphenous artery. Inhibition of nitric oxide synthase attenuated the ACh-rel axation of rings from control and trained animals, but this effect was sign ificantly larger in the vessels from trained animals. These results are con sistent with the idea that nitric oxide could contribute to the enhanced AC h-relaxation of the saphenous artery with exercise training.