Fig. 3. Influence of N^G -nitro-l-arginine (l-NNA) treatment on the positive inotropic effect of isoproterenol in papillary muscles from (A ) control, (B ) 3-h septic, and (C ) 6-h septic rabbits. The concentration-response curves for isoproterenol in the absence (open circles) and presence (filled circles) of 100 μm l-NNA are shown. l-NNA was added to the bath at least 30 min before isoproterenol application. Mean of data from five muscles are presented, with SD shown by vertical lines.