Acute exercise attenuates phenylephrine-induced contraction of rabbit isolated aortic rings

Factors associated with a single bout of dynamic exercise (increased circulating catecholamines, increased body temperature, and decreased pH) are known to attenuate the vascular response to alpha-adrenergic receptor activation. Therefore, we postulate that an acute bout of dynamic exercise may decrease the vascular response to catecholamines. To test this hypothesis, we evaluated contractile responsiveness to phenylephrine (PE) in aortae of two groups of New Zealand white rabbits, a control group (no exercise) and an exercise group (treadmill running, 24m.min-1; 16 +/- 2.0 min). Aortic rings were prepared from age-matched control (N = 6) and exercise rabbits (N = 5) and mounted for isometric tension recording (in Krebs-Henseleit-bicarbonate solution, 37 degrees C, 1.5 g passive tension). After equilibration (2 h) a cumulative concentration-response curve to PE (10(-7) M-10(-2) M) was obtained. The results demonstrate that a single bout of dynamic exercise attenuates (P < 0.05) the maximal contractile tension (2,457 +/- 120 vs 3,620 +/- 321 mg tension.mg-1 ring wt), gain (602 +/- 31 vs 878 +/- 87 mg.M-1 PE), and rate of contraction (6.2 +/- 0.3 vs 4.7 +/- 0.3 mg tension.s-1). In addition, contraction threshold was significantly increased in exercise (2.6 +/- 0.4 x 10(-6) M) vs control aortae (1.03 +/- 0.4 x 10(-6) M). A single bout of dynamic exercise did not alter the contractile response to 70 mM KCl (3,555 +/- 270 vs 3,083 +/- 233 mg tension.mg-1 ring weight). These data suggest that an acute bout of dynamic exercise significantly attenuates alpha-adrenergic receptor-mediated contraction of vascular smooth muscle.