Abstract des Autors

Studies of the effect of nitric oxide (NO) synthesis inhibition were performed in the isometrically contracting blood-perfused canine gastrocnemius-plantaris muscle group. Muscle blood flow (Q) was controlled with a pump during continuous NO blockade produced with either 1 mM L-argininosuccinic acid (L-ArgSA) or NG-nitro-L-arginine methyl ester (L-NAME) during repetitive tetanic contractions (50-Hz trains, 200-ms duration, 1/s). Pump Q was set to match maximal spontaneous Q (1.3-1.4 ml/min/g) measured in prior, brief (3-5 min) control contraction trials in each muscle. Active tension and oxygen uptake were 500-600 g/g and 200-230 micro-l/min/g, respectively, under these conditions. Within 3 min of L-ArgSA infusion, vascular resistance across the muscle (Rv) increased significantly (from ca. 100 to 300 peripheral resistance units; P<0.05), whereas Rv increased to a lesser extent with L-NAME (from ca. 100 to 175 peripheral resistance units; P<0.05). The increase in Rv with L-ArgSA was unchanged by simultaneous infusion of 0.5-10 mM L-arginine but was reduced with 1-3 micro-g/ml sodium nitroprusside (41-54%). The increase in Rv with L-NAME was reversed with 1 mM of L-arginine. Increased fatigue occurred with infusion of L-ArgSA; active tension and intramuscular pressure decreased by 62 and 66%, whereas passive tension and baseline intramuscular pressure increased by 80 and 30%, respectively. These data indicate a possible role for NO in the control of Rv and contractility within the canine gastrocnemius-plantaris muscle during repetitive tetanic contractions. Verf.-Referat