AHEART Mar. 45/3

Frame, Mary D. S. Conducted signals within arteriolar networks initiated by bioactive amino acids. Am. J. Physiol. 276 (Heart Circ. Physiol. 45): H1012–H1021, 1999.—Our purpose was to determine the specificity of L-arginine (L-Arg)induced conducted signals for intravs. extracellular actions of L-Arg. Diameter and red blood cell velocities were measured for arterioles [18 6 1.6 (SE) μm] in the cremaster muscle of pentobarbital sodium-anesthetized (Nembutal, 70 mg/kg) hamsters (n 5 53). Remote (conducted) responses were viewed ,1,000 μm upstream from the local (micropipette) application. Six amino acids were tested: L-arginine, L-cystine, L-leucine, L-lysine, L-histidine, and L-aspartate (100 μM each). Only L-Arg induced a remote dilation; L-lysine and L-aspartate had no effect, and the others each induced a significant remote constriction. There is a second conducted signal initiated by L-arginine that preconditions the arteriolar network and upregulates a direct response of L-arginine to dilate the remote site. This was blocked by inhibition of L-arginine uptake at the local (preconditioning) site (100 μM L-histidine or 1 mM phenformin). Arginine-glycine-aspartate (100 μM)-induced remote dilations (13.2 6 0.3 μm) were not mimicked by a peptide control and were prevented by antiintegrin av monoclonal antibody. Remote dilations were greater in animals with a higher wall shear stress for arginine-glycine-aspartate (r2 5 0.92) but not for L-arginine (r2 5 0.12). Thus L-arginine initiates separate conducted signals related to system y1 transport, integrins, and baseline flow.