Hydrogen sulfide (H2S) is a gaseous mediator, produced by the metabolic pathways that regulate tissue concentrations of sulfur-containing amino acids. Recent studies indicate that endogenous or exogenous H2S exerts physiological effects in the cardiovascular system of vertebrates, possibly through modulation of K ATP channel opening. The present study was undertaken to examine the hypothesis that H2S is cytoprotective against myocardial ischemia-reperfusion injury and that this protective action is mediated by K ATP opening. Rat isolated hearts were Langendorff-perfused and underwent 30 min left main coronary artery occlusion and 120 min reperfusion. The resulting injury was assessed as infarct size, determined by tetrazolium staining. Treatment of hearts with the H2S-donor, NaHS, commencing 10 min prior to the onset of coronary occlusion and maintained until 10 min reperfusion, resulted in a concentration-dependent limitation of infarct size (control, 41.0 +/- 2.6% of risk zone; NaHS 0.1 microM, 33.9 +/- 2.1%, [0.05 > P < 0.1]; NaHS 1 microM, 20.2 +/- 2.1% [P < 0.01]). Pretreatment with the K ATP channel blockers glibenclamide 10 microM or sodium 5-hydroxydecanoate (5HD) 100 microM led to abrogation of the infarct-limiting effect of NaHS 1 microM (glibenclamide + NaHS 42.5 +/- 3.6%; 5HD + NaHS 44.7 +/- 2.2%). No statistically significant effects of NaHS treatment on coronary flow, heart rate or left ventricular developed pressure were observed in this experimental preparation. These data provide the first evidence that exogenous H2S protects against irreversible ischemia-reperfusion injury in myocardium and support the involvement of K ATP opening in the mechanism of action. Further work is required to elucidate the potential role of endogenous H2S as a cytoprotective mediator against myocardial ischemia-reperfusion injury, the mechanisms regulating its generation, and the nature of its interaction with protein targets such as the K ATP channel.

Aim: Gap junction intercellular communication (GJIC) and hemichannel permeability may have important roles during an ischemic insult. Our aim was to evaluate the effect of ischemia on gap junction channels and hemichannels. Methods: We used neonatal rat heart myofibroblasts and simulated ischemia with a HEPES buffer with high potassium, low pH, absence of glucose, and oxygen tension was reduced by dithionite. Microinjection, western blot, immunofluorescence, cell viability and dye uptake were used to evaluate the effects induced by dithionite. Isolated perfused rat hearts were used to analyse infarct size. Results: Short period with simulated ischemia reduced the ability to transfer a dye between neighbouring cells, which indicated reduced GJIC. Prolonged exposure to simulated ischemia caused opening of hemichannels, and cell death was apparent while gap junction channels remained closed. Connexin 43 became partially dephosphorylated and the total amount decreased during simulated ischemia. We were not able to detect the alternative hemichannel-forming protein, Pannexin 1, in these cells. The potential importance of Connexin 43 or Pannexin 1 hemichannels in ischemia-induced infarct in the intact heart was studied by perfusion of the heart in the presence of peptides that block one or the other type of hemichannels. The connexin-derived peptide, Gap26, significantly reduced the infract/risk zone ratio (control 48.7±4.2% and Gap26 19.4±4.1%, p<0.001), while the pannexin-derived peptide, ¹⁰Panx1, did not change infarct/risk ratio. Conclusion: Connexin 43 is most likely responsible for both closure of gap junction channels and opening of hemichannels during simulated ischemia in neonatal rat heart myofibroblasts. Opening of connexin 43 hemichannels during ischemia-reperfusion seems to be an important mechanism for ischemia-reperfusion injury in the heart. By preventing the opening of these channels during early ischemia-reperfusion the infarct size becomes significantly reduced.

BackgroundThere is an increased risk of heart failure and pulmonary edema in pregnancies complicated by hypertensive disorders. However, in a previous study we found that pregnancy protects against fibrosis and preserves angiogenesis in a rat model of angiotensin II induced cardiac hypertrophy. In this study we test the hypothesis that pregnancy protects against negative effects of increased afterload.MethodsPregnant (gestational day 5.5–8.5) and non-pregnant Wistar rats were randomized to transverse aortic constriction (TAC) or sham surgery. After 14.2±0.14 days echocardiography was performed. Aortic blood pressure and left ventricular (LV) pressure-volume loops were obtained using a conductance catheter. LV collagen content and cardiomyocyte circumference were measured. Myocardial gene expression was assessed by real-time polymerase chain reaction.ResultsHeart weight was increased by TAC (p<0.001) but not by pregnancy. Cardiac myocyte circumference was larger in pregnant compared to non-pregnant rats independent of TAC (p = 0.01), however TAC per se did not affect this parameter. Collagen content in LV myocardium was not affected by pregnancy or TAC. TAC increased stroke work more in pregnant rats (34.1±2.4 vs 17.5±2.4 mmHg/mL, p<0.001) than in non-pregnant (28.2±1.7 vs 20.9±1.5 mmHg/mL, p = 0.06). However, it did not lead to overt heart failure in any group. In pregnant rats, α-MHC gene expression was reduced by TAC. Increased in the expression of β-MHC gene was higher in pregnant (5-fold) compared to non-pregnant rats (2-fold) after TAC (p = 0.001). Nine out of the 19 genes related to cardiac remodeling were affected by pregnancy independent of TAC.ConclusionsThis study did not support the hypothesis that pregnancy is cardioprotective against the negative effects of increased afterload. Some differences in cardiac structure, function and gene expression between pregnant and non-pregnant rats following TAC indicated that afterload increase is less tolerated in pregnancy.