The NO donor sodium nitroprusside: evaluation of skeletal muscle vascular and metabolic dysfunction

Abstract

The nitric oxide (NO) donor sodium nitroprusside (SNP) may promote cyanide-induced toxicity and systemic and/or local responses approaching maximal vasodilation. The hypotheses were tested that SNP superfusion of the rat spinotrapezius muscle exerts 1) residual impairments in resting and contracting blood flow, oxygen utilization (VO(2)) and microvascular O(2) pressure (PO(2)mv); and 2) marked hypotension and elevation in resting PO(2)mv. Two superfusion protocols were performed: 1) Krebs-Henseleit (control 1), SNP (300 μM; a dose used commonly in superfusion studies) and Krebs-Henseleit (control 2), in this order; 2) 300 and 1200 μM SNP in random order. Spinotrapezius muscle blood flow (radiolabeled microspheres), VO(2) (Fick calculation) and PO(2)mv (phosphorescence quenching) were determined at rest and during electrically-induced (1 Hz) contractions. There were no differences in spinotrapezius blood flow, VO(2) or PO(2)mv at rest and during contractions pre- and post-SNP condition (control 1 and control 2; p>0.05 for all). With regard to dosing, SNP produced a graded elevation in resting PO(2)mv (p<0.05) with a reduction in mean arterial pressure only at the higher concentration (p<0.05). Contrary to our hypotheses, skeletal muscle superfusion with the NO donor SNP (300 μM) improved microvascular oxygenation during the transition from rest to contractions (PO(2)mv kinetics) without precipitating residual impairment of muscle hemodynamic or metabolic control or compromising systemic hemodynamics. These data suggest that SNP superfusion (300 μM) constitutes a valid and important tool for assessing the functional roles of NO in resting and contracting skeletal muscle function without incurring residual alterations consistent with cyanide accumulation and poisoning.

Fig. 1

Schematic representation of the experimental protocol (diagram not to scale). Group A: Control 1 (Krebs-Henseleit), SNP (300 µM SNP), Control 2 (Krebs-Henseleit). Group B: 300 or 1200 µM SNP superfusion in random order. S, superfusion (3 min); I, incubation (3 min); Stim, electrical stimulation of the right spinotrapezius muscle (3 min); R, recovery and washout (~20 min). See text for further details.

Fig. 2

Spinotrapezius muscle blood flow (top panel) and V̇O₂ (bottom panel) at rest and during the contraction steady-state before and after superfusion with 300 µM SNP (i.e., control 1 and control 2, respectively). Three contraction bouts were performed in the following order: control 1(Krebs-Henseleit), SNP (300 µM), control 2 (Krebs-Henseleit). Note similar spinotrapezius muscle blood flow and V̇O₂ responses between control 1 and control 2 both at rest and during the contraction steady-state (p>0.05 for all). n.s., not significantly different; *p<0.05 vs. rest.

Fig. 3

Top panel depicts the spinotrapezius muscle PO₂mv at rest and during the onset of contractions under distinct superfusion conditions performed in the following order: control 1 (Krebs-Henseleit), SNP (300 µM), control 2 (Krebs-Henseleit). Bottom panel further illustrates the change in muscle PO₂mv with 300 µM SNP (elevated resting and contracting steady-state PO₂mv along with slower speed of PO₂mv fall at contractions onset, see Table 1) and the similarity between control 1 and control 2 (p>0.05 for all kinetics parameters, see Table 1). Time zero denotes the onset of muscle contractions. See text for further details.

Fig. 4

Effects of distinct SNP superfusion concentrations (300 and 1200 µM) on resting MAP (top panel) and spinotrapezius muscle PO₂mv (bottom panel). Note that a four times greater concentration of SNP (1200 µM) evoked greater effects on both resting MAP and PO₂mv when compared to the SNP concentration used currently in our and other laboratories (Behnke and Delp, 2010; Boegehold, 1992; Didion and Mayhan, 1997; Ferreira et al., 2006a; Ferreira et al., 2006b; Hirai et al., 2012; Hirai et al., 2010; Lash and Bohlen, 1997; Muller-Delp et al., 2002; Padilla et al., 2010; Saito et al., 1994; Sato et al., 2008; Trott et al., 2009). Pre, pre-superfusion; post, post-superfusion; delta, difference between pre- and post-superfusion. *p<0.05 vs. pre-superfusion within SNP concentration. †p<0.05 vs. 300 µM SNP within condition.