Figure 3.

Metabolic inhibition of α-adrenergic vasoconstriction is defective in contracting nNOS-deficient skeletal muscle of mdx and nNOS knockout mice. (a and c) Segments of original records from experiments in an mdx mouse (a) and in an nNOS knockout mouse (c) showing the arterial blood pressure (BP) and femoral blood flow velocity (FBF) responses to intraarterial injection of norepinephrine (NE) in resting and contracting hindlimb. In both mice, NE injection in resting hindlimb increased arterial pressure and decreased femoral blood flow velocity (Left in a and c). This NE-mediated vasoconstriction was not attenuated in contracting hindlimbs, indicating that metabolic modulation of α-adrenergic vasoconstriction was impaired in nNOS-deficient muscle (Right in a and c). (b and d) Summary data showing the NE-mediated decreases in calculated femoral vascular conductance (FVC) in resting and contracting (Contr) hindlimb. The NE-mediated decreases in vascular conductance were not attenuated by hindlimb contraction in mdx mice (b; n = 10) or in nNOS knockout mice (d; n = 6).