Increases in Coronary Collateral Blood Flow Produced by Sevoflurane Are Mediated by Calcium-activated Potassium (BKCa) Channels In Vivo

Background Sevoflurane enhances coronary collateral blood flow independent of adenosine triphosphate-regulated potassium channels. The authors tested the hypothesis that this volatile anesthetic increases coronary collateral blood flow by either opening calcium-activated potassium channels or by directly stimulating nitric oxide synthesis in the canine coronary collateral circulation. Methods Twelve weeks after left anterior descending coronary artery ameroid constrictor implantation, barbiturate-anesthetized dogs (n = 22) were instrumented for measurement of hemodynamics and retrograde coronary flow. Dogs received sevoflurane ([0.5 and 1.0 minimum alveolar concentration [MAC]) during intracoronary infusions of drug vehicle (0.9% saline), the calcium-activated potassium channel antagonist iberiotoxin (13 microg/min), or the nitric oxide synthase inhibitor -nitro-l-arginine methyl ester (l-NAME, 300 microg/min). Retrograde coronary collateral blood flow was measured under baseline conditions, during and after administration of sevoflurane, and during intracoronary infusion of bradykinin. Data are mean +/- SEM. Results Sevoflurane increased (* < 0.05) retrograde coronary collateral blood flow (from 65 +/- 11 during control to 67 +/- 12* and 71 +/- 12* ml/min during 0.5 and 1.0 MAC, respectively). Iberiotoxin but not l-NAME attenuated these sevoflurane-induced increases in retrograde flow (6 +/- 1*, 7 +/- 2*, and 3 +/- 2 ml/min during vehicle, l-NAME, and iberiotoxin, respectively). After discontinuation of sevoflurane, retrograde flow returned to baseline values in each group. Bradykinin increased retrograde flow in vehicle- (63 +/- 12 to 69 +/- 12* ml/min) but not in iberiotoxin- (61 +/- 7 to 62 +/- 5 ml/min) or l-NAME-treated dogs (64 +/- 11 to 63 +/- 10 ml/min). Conclusions The results demonstrate that sevoflurane increases coronary collateral blood flow, in part, through activation of calcium-activated potassium channels. This action occurs independent of nitric oxide synthesis.

Is Isoflurane-induced Preconditioning Dose Related?

Background Volatile anesthetics precondition against myocardial infarction, but it is unknown whether this beneficial action is threshold- or dose-dependent. The authors tested the hypothesis that isoflurane decreases myocardial infarct size in a dose-dependent fashion in vivo. Methods Barbiturate-anesthetized dogs (n = 40) were instrumented for measurement of systemic hemodynamics including aortic and left ventricular pressures and rate of increase of left ventricular pressure. Dogs were subjected to a 60-min left anterior descending coronary artery occlusion followed by 3 h of reperfusion and were randomly assigned to receive either 0.0, 0.25, 0.5, 1.0, or 1.25 minimum alveolar concentration (MAC) isoflurane in separate groups. Isoflurane was administered for 30 min and discontinued 30 min before left anterior descending coronary artery occlusion. Results Infarct size (triphenyltetrazolium staining) was 29 +/- 2% of the area at risk in control experiments (0.0 MAC). Isoflurane produced significant (P < 0.05) reductions of infarct size (17 +/- 3, 13 +/- 1, 14 +/- 2, and 11 +/- 1% of the area at risk during 0.25, 0.5, 1.0, and 1.25 MAC, respectively). Infarct size was inversely related to coronary collateral blood flow (radioactive microspheres) in control experiments and during low (0.25 or 0.5 MAC) but not higher concentrations of isoflurane. Isoflurane shifted the linear regression relation between infarct size and collateral perfusion downward (indicating cardioprotection) in a dose-dependent fashion. Conclusions Concentrations of isoflurane as low as 0.25 MAC are sufficient to precondition myocardium against infarction. High concentrations of isoflurane may have greater efficacy to protect myocardium during conditions of low coronary collateral blood flow.

Hyperglycemia reduces coronary collateral blood flow through a nitric oxide-mediated mechanism

We tested the hypothesis that hyperglycemia alters retrograde coronary collateral blood flow by a nitric oxide-mediated mechanism in a canine Ameriod constrictor model of enhanced collateral development. Administration of 15% dextrose to increase blood glucose concentration to 400 or 600 mg/dl decreased retrograde blood flow through the left anterior descending coronary artery to 78 ± 9 and 82 ± 8% of baseline values, respectively. In contrast, saline or l-arginine (400 mg · kg−1 · h−1) had no effect on retrograde flow. Coronary hypoperfusion and 1 h of reperfusion decreased retrograde blood flow similarly in saline- orl-arginine-treated dogs (76 ± 11 and 89 ± 4% of baseline, respectively), but these decreases were more pronounced in hyperglycemic dogs (47 ± 10%). l-Arginine prevented decreases in retrograde coronary collateral blood flow during hyperglycemia (100 ± 5 and 95 ± 6% of baseline at blood glucose concentrations of 400 and 600 mg/dl, respectively) and after coronary hypoperfusion and reperfusion (84 ± 14%). The results suggest that hyperglycemia decreases retrograde coronary collateral blood flow by adversely affecting nitric oxide availability.

Sevoflurane Selectively Increases Coronary Collateral Blood Flow Independent of KATPChannels In Vivo

Background Volatile anesthetic agents produce coronary vasodilation via activation of adenosine triphosphate-sensitive potassium (KATP) channels. The authors tested the hypothesis that sevoflurane selectively increases coronary collateral blood flow and assessed the role of KATP channel activation in this process. Methods Experiments were conducted in dogs 8 weeks after long-term implantation of a left anterior descending coronary artery (LAD) ameroid constrictor to stimulate coronary collateral growth. Dogs were instrumented for measurement of retrograde LAD blood flow (an index of large coronary collateral blood flow) and LAD tissue flow (via radioactive microspheres; an index of small collateral blood flow). Coronary collateral perfusion and normal (left circumflex coronary artery [LCCA]) zone tissue blood flow were determined in four groups of dogs pretreated with intracoronary glyburide (50 microg/kg) or vehicle in the presence or absence of sevoflurane (1 minimum alveolar concentration). Dose-response relationships to the KATP channel agonist nicorandil were established in each dog using doses (25, 50, and 100 microg/min) previously shown to increase coronary collateral blood flow. Results Sevoflurane increased blood flow through large and small collaterals and increased collateral vascular conductance in the presence of glyburide but did not affect LCCA blood flow or conductance. In contrast, nicorandil increased blood flow through small but not large collaterals. Nicorandil also increased LCCA blood flow and conductance, actions that were attenuated by glyburide. Conclusions The results demonstrate that sevoflurane selectively increases large and small coronary collateral blood flow via mechanism(s) independent of KATP channel activation.