Changes in dog gracilis muscle adenosine during exercise and acetate infusion

We have previously reported that tissue acetate content increases in the canine gracilis muscle during exercise at natural flow. We here report the effects of exercise and infusion of acetate on adenosine content. Muscles were vascularly isolated, perfused naturally, and stimulated to contract isometrically at 0.5, 1.0, or 2.0 Hz for 10 min (n = 6 each). Exercising and contralateral control gracilis muscles were freeze clamped in situ in Wollenberger tongs at the temperature of liquid N2. Force development was maintained during contraction. Resistance decreased as a function of contraction frequency, and adenosine content increased. Tissue adenosine content correlated inversely with resistance (r = -0.57, P less than 0.001), suggesting a role for adenosine in exercise hyperemia. During intra-arterial infusion of sodium acetate into resting muscle, tissue acetate and adenosine contents increased (417-2,193 and 0.88-3.07 nmol/g, respectively), and vascular resistance decreased (17.5-6.01 mmHg X ml-1/min/100 g). Acetate and adenosine contents correlated negatively with resistance (r = -0.83, P less than 0.001, and r = -0.60, P less than 0.05, respectively) and positively with one another (r = 0.58, P less than 0.05). Relative to an infusion of sodium chloride, oxygen consumption, venous PO2, and venous ionized calcium were unaffected. The vasodilatory effect of acetate may be due, in part, to its ability to increase tissue adenosine.