Impact of noradrenaline, adrenergic receptors, and radical formation on cardiac mitochondria in resuscitated swine.

BACKGROUND

Equivocal data exist on whether noradrenaline during resuscitation from circulatory shock affects tissue mitochondrial respiration. Therefore, we examined the relation between myocardial mitochondrial respiration and plasma noradrenaline concentrations during continuous i.v. noradrenaline.

METHODS

After anesthesia and (neuro)surgical instrumentation, pigs underwent two hours of subdural blood injection and subsequent systemic blood removal, followed by fluid resuscitation, re-transfusion of shed blood, and noradrenaline to maintain cerebral perfusion pressure at pre-shock levels. Before, immediately after the challenge, and after 48 h of resuscitation, we measured whole blood superoxide anion levels (electron spin resonance) and DNA strand breaks ("tail moment" in the comet assay), and plasma noradrenaline (HPLC/tandem mass-spectrometry), NOx (chemoluminescence), isoprostane and troponin (ELISA) concentrations. Immediate post mortem myocardial samples were analyzed for mitochondrial respiration (high-resolution respirometry for Complex I/II activity, oxidative phosphorylation, and maximal uncoupled electron transfer capacity) as well as β1-/β2-adrenergic receptor and mitochondrial complex I/II expression, and nitrotyrosine formation (immunohistochemistry).

RESULTS

At 48 h of resuscitation, plasma noradrenaline concentrations were 200-fold those at baseline, while NOx levels had doubled. Myocardial mitochondrial respiration was unrelated to noradrenaline, NOx, or nitrotyrosine, but directly related to both the β1- and β2-adrenoceptor expression (oxidative phosphorylation: r = 0.466, p = 0.059 and r = 0.750, p = 0.0005, respectively; maximal uncoupled electron transfer capacity: r = 0.514, p = 0.035 and r = 0.772, p = 0.0003, respectively). Oxidative phosphorylation was inversely related to the plasma troponin-I levels (r = -0.479, p = 0.060). While plasma NOx levels correlated with plasma noradrenaline levels (r = 0.519, p = 0.033), whole blood superoxide anion levels and cardiac nitrotyrosine formation did not.

CONCLUSIONS

In a long-term, resuscitated porcine model of acute subdural hematoma and hemorrhage, plasma NOx levels correlated with noradrenaline plasma levels, whereas mitochondrial respiration and other markers of radical formation or oxidative/nitrosative stress were unrelated to noradrenaline concentrations. β-adrenergic receptor expression was also unrelated to noradrenaline, while mitochondrial respiration was directly related to both the β1- and β2-adrenoceptor expression. Our results suggest that the impaired mitochondrial respiration reported during septic shock for skeletal muscle may be absent in the heart during continuous i.v. noradrenaline for resuscitation from trauma-and-hemorrhage. Nevertheless, cardiac tissue injury is associated with reduced mitochondrial respiration.