Glibenclamide enhances but pinacidil reduces attenuation in sympathetic responsiveness after acute coronary artery occlusion

The effects of levosimendan and glibenclamide on circulatory and metabolic variables in a canine model of acute hypoxia

PURPOSE

To study the effects of pretreatment with levosimendan (LEVO, a Ca²(+)-sensitizer and K (ATP) (+) channel opener) and/or the K (ATP) (+) channel antagonist glibenclamide (GLIB) on systemic hemodynamics, metabolism, and regional gastromucosal oxygenation during hypoxic hypoxemia.

METHODS

Chronically instrumented, healthy dogs (24-32 kg, n = 6 per group, randomized cross-over design) were repeatedly sedated, mechanically ventilated (FiO₂ ~0.3) and subjected to the following interventions: no pretreatment, LEVO pretreatment, GLIB pretreatment, or combined LEVO + GLIB pretreatment, each followed by hypoxic hypoxemia (FiO₂ ~0.1). We measured cardiac output (CO, ultrasonic flow probes), oxygen consumption (VO₂, indirect calorimetry), and gastromucosal microvascular hemoglobin oxygenation (μHbO₂, spectrophotometry).

STATISTICS

data are presented as mean ± SEM and compared by one-way ANOVA (direct drug effects within group) and two-way ANOVA (between all hypoxic conditions) both with Bonferroni corrections; p < 0.05.

RESULTS

In LEVO-pretreated hypoxemia, CO was significantly higher compared to unpretreated hypoxemia. The increased CO was neither associated with an increased VO₂ nor with markers of aggravated anaerobiosis (pH, BE, lactate). In addition, LEVO pretreatment did not further compromise gastromucosal μHbO₂ in hypoxemia. After combined LEVO + GLIB pretreatment, systemic effects of GLIB were apparent, however, CO was significantly higher than during unpretreated and GLIB-pretreated hypoxemia, but equal to LEVO-pretreated hypoxemia, indicating that GLIB did not prevent the increased CO in LEVO-pretreated hypoxia.

CONCLUSIONS

LEVO pretreatment resulted in improved systemic circulation (CO) during hypoxemia without fueling systemic VO₂, without aggravating systemic anaerobiosis markers, and without further compromising microvascular gastromucosal oxygenation. Thus, LEVO pretreatment may be an option to support the systemic circulation during hypoxia.

Effect of ATP-sensitive potassium channel agonists on sympathetic hyperinnervation in postinfarcted rat hearts

Although the acute administration of ATP-sensitive potassium (KATP) channel agonists provides a neuroprotection, it is unclear whether similar benefits are found by modulating sympathetic innervation in chronic settings after myocardial infarction. We assessed whether KATP channel agonists can attenuate the sprouting of cardiac sympathetic nerves after infarction. Male Wistar rats after ligating coronary artery were randomized to either saline, nicorandil, pinacidil, glibenclamide, or a combination of 1) nicorandil and glibenclamide or 2) pinacidil and glibenclamide for 4 wk. To elucidate the role of mitochondrial KATP channels in modulating nerve growth factor, 5-hydroxydecanoate was assessed in an in vitro model. The measurement of myocardial norepinephrine levels revealed a significant elevation in saline-treated infarcted rats compared with sham-operated rats, consistent with excessive sympathetic innervation. Excessive sympathetic innervation was blunted after giving the rats either nicorandil or pinacidil, compared with saline, as assessed by the immunohistochemical analysis of tyrosine hydroxylase, growth associated protein-43, and neurofilament and Western blot analysis and real-time quantitative RT-PCR of nerve growth factor. The arrhythmic scores during programmed stimulation in the saline- or glibenclamide-treated infarcted rats were significantly higher than those of rats treated with KATP channel agonists. In contrast, the beneficial effects of nicorandil and pinacidil were abolished by administering either glibenclamide or 5-hydroxydecanoate. The sympathetic hyperinnervation after infarction is attenuated by the activation of mitochondrial KATP channels. The chronic use of mitochondrial KATP channel agonists after infarction may attenuate the arrhythmogenic response to programmed electrical stimulation.

Haemodynamic and other effects of sulphonylurea drugs on the heart

Antidiabetic sulphonylureas have attracted a great deal of interest in experimental cardiology to evaluate the role of ATP-sensitive potassium channels in the cardiovascular system. It is well established that KATP channels are present in cardiac cells and also in vascular smooth muscle cells and are implicated in the regulation of myocardial and vascular function. It follows that drugs which open, or inhibit the opening of these channels, might profoundly modify cardiovascular function both under physiological and pathophysiological conditions. This paper reviews the evidence for the role of KATP channels in the cardiovascular system and discusses how the different generations of sulphonylurea drugs interfere with cardiac function. We will particularly concentrate on the haemodynamic effects of different sulphonylureas and shortly discuss how these drugs modify ischaemia-reperfusion arrhythmias.