Diane Godin-Ribuot

Protective effects of melatonin against ischemia-reperfusion injury in the isolated rat heart.

There has been increased interest in melatonin recently, since it was shown to be a potent scavenger of toxic free radicals. Melatonin has been found to be effective in protecting against pathological states due to reactive oxygen species release. The present study was performed in order to determine whether melatonin or 5-methoxy-carbonylamino-N-acetyl-tryptamine (5-MCA-NAT), a structurally related indole compound, protect against ischemia-reperfusion injury in the isolated rat heart. Wistar rats were treated in vivo with either melatonin (1 or 10 mg/kg, i.p.) or 5-MCA-NAT (10 mg/kg, i.p.) or their vehicle, 30 min before their hearts were excised and perfused according to the Langendorff technique. Two different protocols were then applied. In the first one, a regional ischemia (5 min)-reperfusion (30 min) sequence was performed in order to record incidence and duration of reperfusion arrhythmias. In the second one, infarct size was assessed after a regional ischemia (30 min)-reperfusion (120 min) sequence. Results show a spectacular protection against ischemia-reperfusion injuries (on arrhythmias as well as on infarct size) in rats pre-treated with 10 mg/kg of melatonin or 5-MCA-NAT. In conclusion, both melatonin and its structural analog, 5-MCA-NAT, appear to confer protection against ischemia-reperfusion injury in the isolated rat heart. This observation suggests that melatonin could have a potential clinical application in the treatment of myocardial ischemia, even if the mechanisms underlying this protection remain to be determined.

Association of urinary 15-F2t-isoprostane level with oxygen desaturation and carotid intima-media thickness in nonobese sleep apnea patients

Obstructive sleep apnea (OSA) is characterized by recurrent apnea during sleep that may unbalance oxidative stress, increasing atherosclerosis. Among oxidative stress markers, 15-F(2t)-isoprostane is considered one of the most sensitive and specific metabolites of lipid peroxidation. To explore the relationship between urinary 15-F(2t)-isoprostane with sleep apnea severity and carotid modifications in nonobese OSA patients, 31 nonobese sleep apnea patients were studied, along with 10 lean subjects without OSA. Patients were assessed by polysomnography, blood pressure measurement, and ultrasonography to determine the carotid intima-media thickness (IMT). Urinary 15-F(2t)-isoprostanes were measured by liquid chromatography-tandem mass spectrometry. Urinary 15-F(2t)-isoprostane concentrations were increased in severe OSA patients compared to control subjects (20.2+/-7.3 vs 12.3+/-2.8 ng/mmol creatinine; P=0.020). Mean carotid IMT was correlated with 15-F(2t)-isoprostane (r=0.532; P<0.001) and with the apnea-hypopnea index (r=0.345; P=0.029). 15-F(2t)-Isoprostane level was related to the night time spent at SaO(2)<90% (r=0.478; P=0.002), the apnea-hypopnea index (r=0.465; P=0.003), and the mean nocturnal SaO(2) (r=-0.424; P=0.007). These results showed a relationship between lipid peroxidation, carotid intima-media thickness, and intermittent hypoxia in nonobese OSA patients, thus reinforcing the hypothesis that oxidative stress could be involved in the early atherosclerotic process.

Resistance to myocardial infarction induced by heat stress and the effect of ATP-sensitive potassium channel blockade in the rat isolated heart

1 Heat stress (HS) is known to protect against myocardial ischaemia‐reperfusion injury by improving mechanical dysfunction and decreasing necrosis. However, the mechanisms responsible for this form of cardioprotection remain to be elucidated. ATP‐sensitive potassium (KATP) channels have been shown to be involved in the delayed phase of protection following ischaemic preconditioning, a phenomenon closely resembling the HS‐induced cardioprotection. The aim of this study was thus to investigate the role of KATP channels in HS‐induced protection of the isolated rat heart. 2 Twenty four hours after whole body heat stress (at 42°C for 15u2003min) or sham anaesthesia, isolated perfused hearts were subjected to a 15u2003min stabilization period followed by a 15u2003min infusion of either 10u2003μM glibenclamide (Glib), 100u2003μM sodium 5‐hydroxydecanoate (5HD) or vehicle (0.04% DMSO). Regional ischaemia (35u2003min) and reperfusion (120u2003min) were then performed. 3 Prior heat stress significantly reduced infarct‐to‐risk ratio (from 42.4±2.4% to 19.4±2.9, P<0.001). This resistance to myocardial infarction was abolished in both Glib‐treated (40.1±1.8% vs 42.3±1.8%) and 5HD‐treated (41.2±1.8% vs 41.8±1.2%) groups. 4 The results of this study suggest that KATP channel activation contributes to the cytoprotective response induced by heat stress.

Heat stress fails to protect myocardium of streptozotocin-induced diabetic rats against infarction

OBJECTIVEnProtection conferred by heat stress (HS) against ischaemia-reperfusion injury, in term of mechanical function and myocardial necrosis, has been extensively studied. In contrast, the effects of disease states on this HS-induced cytoprotective response are less known. Therefore, we investigated the effects of prior heat stress on the infarct size in the isolated heart and on the myocardial heat stress protein (HSP) 72 synthesis, in a model of insulin-dependent diabetic rats.nnnMETHODSnThree groups of animals were studied: D rats were rendered diabetic by 55 mg/kg streptozotocin i.v. injection. DI rats received the same treatment plus a daily injection of insulin started 2 weeks after and V rats received the vehicle of streptozotocin plus a daily injection of saline. Eight weeks later, D, DI and V rats were either heat-stressed (42 degrees C for 15 min) or sham-anaesthetised. Twenty-four hours later, their hearts were isolated, perfused using the Langendorff technique, and subjected to a 30 min occlusion of the left coronary artery followed by 120 min of reperfusion. Myocardial HSP72 content was measured 24 h after HS or sham treatment using an electrophoresis coupled with a Western blot analysis.nnnRESULTSnInfarct-to-risk ratio (I/R) was significantly reduced in hearts from heat-stressed (11.7 +/- 2.0%) compared to sham (30.0 +/- 3.2%) V rats. This cardioprotection was not observed in hearts from D (I/R: 31.4 +/- 3.3 vs. 34.3 +/- 3.5%) and DI (I/R: 28.7 +/- 1.6 vs. 30.3 +/- 1.6%) rats. Risk zones were similar between all experimental groups. The incidence of ventricular arrhythmias during ischaemia and reperfusion periods was not different between the six experimental groups. Western blot analysis of the myocardial HSP72 content showed a comparable heat stress-induced increase of this protein, in V, D and DI animals.nnnCONCLUSIONnThese results demonstrate that myocardial protective effect induced by heat stress could not extend to a pathological animal model like the diabetic rat and seems to be unrelated to the HSP72 level. Further investigations are required to elucidate the precise role of the heat stress proteins in this adaptive response.

SB 203580, a mitogen-activated protein kinase inhibitor, abolishes resistance to myocardial infarction induced by heat stress.

Heat stress (HS) is known to confer protection against ischemia-reperfusion injury, including mechanical dysfunction and myocardial necrosis. However, the mechanisms involved in this cardioprotection are yet to be elucidated. Mitogen-activated protein (MAP) kinase cascades have been demonstrated to be involved in cellular response to different stresses. In particular, p38 MAP kinase is known to be activated by HS. Therefore, we investigated the implication of this kinase in HS-induced resistance to myocardial infarction, in the isolated rat heart model, using SB 203580 (SB) to selectively inhibit p38 MAP kinase. Rats were treated with SB (2.83 mg/kg, i.p.) or vehicle (1% DMSO in saline, i.p.) before they were either heat stressed (42°C for 15 minutes) or sham anesthetized. Their hearts were isolated 24 hours later, retrogradely perfused, and subjected to a 35-minute occlusion of the left coronary artery followed by 120 minutes of reperfusion. The infarct-to-risk ratio was significantly reduced in HS (16.9 ± 2.0%) compared with sham (41.6 ± 2.5%) hearts. This reduction in infarct size was abolished in the SB 203580–treated group (37.8 ± 1.9% in HS + SB vs. 42.0 ± 1.9% in sham + SB). Risk zones were similar between experimental groups. Western blot analysis of the myocardial HSP72 showed an HS-induced increase of this protein, which was not modified by the p38 MAP kinase inhibitor, SB 203580. We conclude that activation of p38 MAP kinase appears to play a role in the functional cardioprotection associated with the heat stress response, which seems to be unrelated to the HSP72 level. Further investigations are required to elucidate the precise role of the p38 MAP kinase and heat stress proteins in this adaptative response.

Highly Protective Effects Of Chronic Oral Administration Of Nicorandil On The Heart Of Ageing Rats

1.u2002We have tested the effects of 2 month oral treatment with the KATP opener, nitric oxide (NO) donor and anti‐oxidant molecule nicorandil (0.1 mg/kg per day) on major physiological parameters and heart function of 4‐, 12‐ and 24‐month‐old rats.

Heat stress-induced protection of endothelial function against ischaemic injury is abolished by ATP-sensitive potassium channel blockade in the isolated rat heart

The protection conferred by heat stress (HS) against myocardial ischaemia‐reperfusion injury, in terms of mechanical function preservation and infarct size reduction, is well documented and mechanisms underlying these effects have been extensively explored. However, the effect of HS on coronary circulation is less known. The aim of this study was thus to investigate the role of ATP‐sensitive potassium (KATP) channels in the protection against ischaemic injury afforded by HS to the coronary endothelial function. Twenty‐four hours after whole body hyperthermia (42°C for 15u2003min, H groups) or sham anaesthesia (Sham groups), isolated perfused rat hearts were subjected to a 15u2003min stabilization period followed by a 30u2003min infusion of either 0.3u2003μM glibenclamide (Gli, a KATP channel blocker) or its vehicle (V). Hearts were then exposed to a low‐flow ischaemia (30u2003min)‐reperfusion (20u2003min) (I/R) or normally perfused (50u2003min), after which coronaries were precontracted with 0.1u2003μM U‐46619. Finally, the response to the endothelium‐dependent vasodilator, 5‐hydroxytryptamine (5‐HT, 10u2003μM) was compared to that of the endothelium‐independent vasodilator, sodium nitroprusside (SNP, 3u2003μM). In hearts from Sham‐V and Sham‐Gli groups, I/R selectively diminished 5‐HT‐induced vasodilatation without affecting the vasodilatation to SNP. In V‐treated groups, prior HS preserved the vasodilatation produced by 5‐HT. This HS‐induced protection was abolished by Gli treatment. In conclusion, these results suggest that KATP channel activation contributes to the preservation of coronary endothelial function conferred by heat stress against ischaemic insult.

Infarct size-reducing effect of heat stress and α1 adrenoceptors in rats

1 Noradrenaline (NA), which is abundantly released during heat stress (HS), is known to induce both delayed cardioprotection and heat stress protein (HSP) 72 expression by the mediation of α1 adrenoceptors. Therefore, we have investigated the implication of α1 adrenoceptors in HS‐induced resistance to myocardial infarction, in the isolated rat heart model. 2 Rats were pretreated with prazosin (1u2003mgu2003kg−1, i.p., Praz) or 5‐methylurapidil (3u2003mgu2003kg−1, i.v, 5MU) or chloroethylclonidine (3u2003mgu2003kg−1, i.v., CEC) or vehicle (V) in order to selectively antagonize α1, α1A and α1B adrenoceptors. They were then either heat stressed (42°C for 15u2003min) or sham anaesthetized. Twenty‐four hours later, their hearts were isolated, retrogradely perfused, and subjected to a 30u2003min occlusion of the left coronary artery followed by 120u2003min of reperfusion. 3 Infarct‐to‐risk ratio was significantly reduced in HS+V (15.4±1.8%) compared to Sham+V (35.7±1.3%) hearts. This effect was abolished in Praz‐treated (29.1±1.6% in HS+Praz vs 34.1±4.0% in Sham+Praz), 5MU‐treated (34.5±2.2% in HS+5MU vs 31.2±2.0% in Sham+5MU) and CEC‐treated (33.4±3.0% in HS+CEC vs 32.4±1.3% in Sham+CEC) groups. Western blot analysis of myocardial HSP72 showed an HS‐induced increase of this protein, which was not modified by Praz, 5MU and CEC pretreatments. 4 We conclude that both α1A and α1B adrenoceptor subtypes appear to play a role in the heat stress‐induced cardioprotection, independently of the HSP72 level. Further investigations are required to elucidate the precise role of HSPs in this adaptative response.

Heat stress response and myocardial protection.

Abstract— Prior whole‐body hyperthermia is able to protect the myocardium against ischaemia‐reperfusion injury by reducing cellular necrosis, preserving the ventricular function and preventing the occurrence of arrhythmias. These cardioprotective effects are associated with reduction of oxidative stress, preservation of the high‐energy phosphate levels and synthesis of heat stress proteins. A better understanding of this powerful protective adaptation of the myocytes would be of interest for potential clinical application, and rational design of specific agents that activate this mechanism will hopefully follow soon.

Heat stress-induced B1 receptor synthesis in the rat: an ex vivo study

1 This ex vivo study was performed to characterize B1 receptor induction in rats submitted to heat stress. Changes in aortic isometric tension were recorded after a 90u2003min in vitro incubation with [des‐Arg9]‐bradykinin. B1 receptor mRNA were detected in aorta and heart using RT–PCR technique. 2 Aortic rings from sham rats did not respond to [des‐Arg9]‐bradykinin. In contrast, this agonist induced a concentration‐dependent relaxation of aortic rings from rats submitted to lipopolysaccharide (LPS) treatment or to heat stress 24u2003h earlier. 3 The concentration‐dependent relaxation induced by [des‐Arg9]‐bradykinin on aortic rings from heat‐stressed rats was abolished by [des‐Arg10]‐HOE 140, a selective B1 receptor antagonist. 4 In endothelium denuded aortic rings from heat‐stress rats, [des‐Arg9]‐bradykinin induced a concentration‐dependent constriction. 5 Pretreatment of intact aortic rings from heat‐stress rats with the cyclo‐oxygenase inhibitor, diclofenac (1u2003μM) did not prevent the concentration‐dependent relaxation in response to [des‐Arg9]‐bradykinin. In contrast, NO synthase inhibition with Nω‐nitro‐L‐arginine methyl ester (30u2003μM) totally prevented the vasorelaxant response. 6 B1 receptor mRNA were not detected in aorta and heart from sham animals but were present in tissue from heat‐stressed and LPS‐treated rats. 7 In conclusion, our results suggest that heat stress induces a transcriptional activation of the B1 receptor gene. The induction of B1 receptors leads to an endothelium‐ and NO‐dependent vasorelaxant response to [des‐Arg9]‐bradykinin.