Effects of N^ω-nitro-L-arginine (L-NOARG) on blood flow and vasomotion in rat diaphragm microcirculation during hemorrhagic hypotension

The role of N^ω-nitro-L-arginine (L-NOARG), a nitric oxide (NO) synthase inhibitor, in the control of blood flow and vasomotion in rat diaphragm microcirculation during hemorrhagic hypotension was investigated by means of laser Doppler flowmetry (LDF). Fifty-six Sprague-Dawley rats were divided into seven groups. Ten minutes after one-stage hemorrhage to 40-60% of initial blood pressure, the rats received 15 min topical superfusion of saline (group 1, time control), 0.1 mM L-NOARG (group 2), 10 mM L-arginine (group 3), or vehicle (0.1% DMSO and 0.9 mN NaOH, group 4). For groups 5 and 6, L-NOARG or its vehicle was superfused for 15 min without hemorrhage. In group 7, the vasodilator responses to the endothelium-dependent vasorelaxant acetylcholine (ACH) and the endothelium-independent vasorelaxant sodium nitroprusside (SNP) were assessed at rest and after 25 min of hemorrhagic hypotension. The results showed no significant differences in blood flow, fundamental frequency, or relative amplitude of the rat diaphragm microcirculation before or after administration of the test agents among the first four groups during hemorrhagic hypotension or in groups 5 and 6 during sham operation without hypoperfusion. Hemorrhagic hypotension significantly decreased the vasodilator response to ACH (p = 0.003), but not to SNP. We conclude that NO did not play an important role in the regulation of blood flow or vasomotion in rat diaphragm microcirculation during acute hemorrhagic hypotension.