Effects of altered nitric oxide availability on rat muscle microvascular oxygenation during contractions.

Aim: To explore the role of nitric oxide (NO) in controlling microvascular O2 pressure (P(O2)mv) at rest and during contractions (1 Hz). We hypothesized that at the onset of contractions sodium nitroprusside (SNP) would raise P(O2)mv and slow the kinetics of P(O2)mv change whereas l-nitro arginine methyl ester (L-NAME) would decrease P(O2)mv and speed its kinetics.
Methods: We superfused the spinotrapezius muscle of female Sprague-Dawley rats (n = 7, body mass = 298 +/- 10 g) with SNP (300 microM) and L-NAME (1.5 mm) and measured P(O2)mv (phosphorescence quenching) during contractions.
Results: SNP decreased mean arterial pressure (92 +/- 5 mmHg) below that of control (CON, 124 +/- 4 mmHg) and L-NAME (120 +/- 4 mmHg) conditions. SNP did not raise P(O2)mv at rest but it did elevate the P(O2)mv-to-MAP ratio (50% increase, P < 0.05) and slow the kinetics by lengthening the time-delay (TD, 14.0 +/- 5.0 s) and time constant (tau, 24.0 +/- 10.0 s) of the response compared with CON (TD, 8.4 +/- 3.3 s; tau, 16.0 +/- 4.5 s, P < 0.05 vs. SNP). L-NAME decreased P(O2)mv at rest and tended to speed tau (10.1 +/- 3.8 s, P = 0.1), while TD (8.1 +/- 1.0 s) was not significantly different. L-NAME also caused P(O2)mv to fall transiently below steady-state contracting values.
Conclusions: These results indicate that NO availability can significantly affect P(O2)mv at rest and during contractions and suggests that P(O2)mv derangements in ageing and chronic disease conditions may potentially result from impairments in NO availability.