Lidocaine impairs vasodilation mediated by adenosine triphosphate-sensitive K+ channels but not by inward rectifier K+ channels in rat cerebral microvessels

Mepivacaine attenuates vasodilation induced by ATP-sensitive potassium channels in rat aorta

The goal of this in vitro study was to investigate the effect of mepivacaine on vasodilation induced by the ATP-sensitive potassium (K_ATP) channel opener levcromakalim in isolated endothelium-denuded rat aortas. The effects of mepivacaine and the K_ATP channel inhibitor glibenclamide, alone or in combination, on levcromakalim-induced vasodilation were assessed in the isolated aortas. The effects of mepivacaine or combined treatment with a protein kinase C (PKC) inhibitor, GF109203X, and mepivacaine on this vasodilation were also investigated. Levcromakalim concentration-response curves were generated for isolated aortas precontracted with phenylephrine or a PKC activator, phorbol 12,13-dibutyrate (PDBu). Further, the effects of mepivacaine and glibenclamide on levcromakalim-induced hyperpolarization were assessed in rat aortic vascular smooth muscle cells. Mepivacaine attenuated levcromakalim-induced vasodilation, whereas it had no effect on this vasodilation in isolated aortas pretreated with glibenclamide. Combined treatment with GF109203X and mepivacaine enhanced levcromakalim-induced vasodilation compared with pretreatment with mepivacaine alone. This vasodilation was attenuated in aortas precontracted with PDBu compared with those precontracted with phenylephrine. Mepivacaine and glibenclamide, alone or in combination, attenuated levcromakalim-induced membrane hyperpolarization. Taken together, these results suggest that mepivacaine attenuates vasodilation induced by K_ATP channels, which appears to be partly mediated by PKC.

Arterial spin-labelling perfusion MRI and outcome in neonates with hypoxic-ischemic encephalopathy

PURPOSE

Hyperperfusion may be related to outcome in neonates with hypoxic-ischemic encephalopathy (HIE). The purpose of this study was to evaluate whether arterial spin labelling (ASL) perfusion is associated with outcome in neonates with HIE and to compare the predictive value of ASL MRI to known MRI predictive markers.

METHODS

Twenty-eight neonates diagnosed with HIE and assessed with MR imaging (conventional MRI, diffusion-weighted MRI, MR spectroscopy [MRS], and ASL MRI) were included. Perfusion in the basal ganglia and thalami was measured. Outcome at 9 or 18 months of age was scored as either adverse (death or cerebral palsy) or favourable.

RESULTS

The median (range) perfusion in the basal ganglia and thalami (BGT) was 63 (28-108) ml/100 g/min in the neonates with adverse outcome and 28 (12-51) ml/100 g/min in the infants with favourable outcome (p < 0.01). The area-under-the-curve was 0.92 for ASL MRI, 0.97 for MRI score, 0.96 for Lac/NAA and 0.92 for ADC in the BGT. The combination of Lac/NAA and ASL MRI results was the best predictor of outcome (r(2) = 0.86, p < 0.001).

CONCLUSION

Higher ASL perfusion values in neonates with HIE are associated with a worse neurodevelopmental outcome. A combination of the MRS and ASL MRI information is the best predictor of outcome.

KEY POINTS

• Arterial spin labelling MRI can predict outcome in neonates with hypoxic-ischemic encephalopathy • Basal ganglia and thalami perfusion is higher in neonates with adverse outcome • Arterial spin labelling complements known MRI parameters in the prediction of outcome • The combined information of ASL and MRS measurements is the best predictor of outcome.

Potassium channels and neurovascular coupling

Neuronal activity is communicated to the cerebral vasculature so that adequate perfusion of brain tissue is maintained at all levels of neuronal metabolism. An increase in neuronal activity is accompanied by vasodilation and an increase in local cerebral blood flow. This process, known as neurovascular coupling (NVC) or functional hyperemia, is essential for cerebral homeostasis and survival. Neuronal activity is encoded in astrocytic Ca(2+) signals that travel to astrocytic processes (;endfeet') encasing parenchymal arterioles within the brain. Astrocytic Ca(2+) signals cause the release of vasoactive substances to cause relaxation, and in some circumstances contraction, of the smooth muscle cells (SMCs) of parenchymal arterioles to modulate local cerebral blood flow. Activation of potassium channels in the SMCs has been proposed to mediate NVC. Here, the current state of knowledge of NVC and potassium channels in parenchymal arterioles is reviewed.

Randomized, double-blinded, placebo controlled study of neuroprotection with lidocaine in cardiac surgery

BACKGROUND AND PURPOSE

Cognitive decline after cardiac surgery remains common and diminishes patients' quality of life. Based on experimental and clinical evidence, this study assessed the potential of intravenously administered lidocaine to reduce postoperative cognitive dysfunction after cardiac surgery using cardiopulmonary bypass.

METHODS

After IRB approval, 277 patients undergoing cardiac surgery were enrolled into this prospective, randomized, double-blinded placebo controlled clinical trial. Subjects were randomized to receive: (1) Lidocaine as a 1 mg/kg bolus followed by a continuous infusion through 48 hours postoperatively, or (2) Placebo bolus and infusion. Cognitive function was assessed preoperatively and again at 6 weeks and 1 year postoperatively. The effect of lidocaine on postoperative cognition was tested using multivariable regression modeling; P<0.05 was considered significant.

RESULTS

Among the 241 allocated subjects (Lidocaine: n=114; Placebo: n=127), the incidence of cognitive deficit in the lidocaine group was 45.5% versus 45.7% in the placebo group (P=0.97). Multivariable analysis revealed a significant interaction between treatment group and diabetes, such that diabetic subjects receiving lidocaine were more likely to suffer cognitive decline (P=0.004). Secondary analysis identified total lidocaine dose (mg/kg) as a significant predictor of cognitive decline and also revealed a protective effect of lower dose lidocaine in nondiabetic subjects.

CONCLUSIONS

Lidocaine administered during and after cardiac surgery does not reduce the high rate of postoperative cognitive dysfunction. Higher doses of lidocaine and diabetic status were independent predictors of cognitive decline. Protective effects of lower dose lidocaine in nondiabetic subjects need to be further evaluated.

Vasodilation mediated by inward rectifier K+ channels in cerebral microvessels of hypertensive and normotensive rats

Although inward rectifier K+ channels contribute to the regulation of cerebral circulation, dilation of cerebral microvasculature mediated by these channels has not been demonstrated in chronic hypertension. We designed the present study to examine the roles of inward rectifier K+ channels in the vasodilation produced by increased levels of extracellular K+ in cerebral parenchymal arterioles from hypertensive and normotensive rats. During constriction to prostaglandin F2alpha (5 x 10(-7) M), the arterioles within brain slices were evaluated using computer-assisted microscopy. Potassium chloride (KCl) induced vasodilation in cerebral arterioles from normotensive (5-10 mM) and hypertensive (5-15 mM) rats, whereas an inward rectifier K+ channel antagonist barium chloride (BaCl2; 10(-5) M) completely abolished the vasodilation in both strains. In arterioles of hypertensive rats, vasodilator responses to KCl were augmented compared with those in normotensive rats. In contrast, the vasodilator responses induced by sodium nitroprusside (3 x 10(-8) to 3 x 10(-6) M) in these two strains were similar. These results suggest that in cerebral cortex parenchymal microvessels, inward rectifier K+ channels play a crucial role in vasodilation produced by extracellular K+ and that the dilation of cerebral arterioles via these channels is augmented in chronic hypertension.