Arrhythmia and sudden death associated with elevated cardiac chloride channel activity

The identification and analysis of several cationic ion channels and their associated genes have greatly improved our understanding of the molecular and cellular mechanisms of cardiac arrhythmia. Our objective in this study was to examine the involvement of anionic ion channels in cardiac arrhythmia. We used a transgenic mouse model to overexpress the human cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes a cAMP-regulated chloride channel. We used RNase protection and in situ hybridization assays to determine the level of CFTR expression, and radiotelemetry and in vivo electrophysiological study in combination with pharmacological intervention to analyse the cardiac function. Cardiac CFTR overexpression leads to stress-related sudden death in this model. In vivo intracardiac electrophysiological studies performed in anaesthetized mice showed no significant differences in baseline conduction parameters including atrial-His bundle (AH) or His bundle-ventricular (HV) conduction intervals, atrioventricular (AV) Wenckebach or 2:1 AV block cycle length and AV nodal functional refractory period. However, following isoproterenol administration, there was marked slowing of conduction parameters, including high-grade AV block in transgenic mice, with non-sustained ventricular tachycardia easily inducible using programmed stimulation or burst pacing. Our sudden death mouse model can be a valuable tool for investigation of the role of chloride channels in arrhythmogenesis and, potentially, for future evaluation of novel anti-arrhythmic therapeutic strategies and pharmacological agents.

The neonatal but not the mature heart adapts to acute tachycardia by beneficial modification of the force-frequency relationship

The force-frequency relationship (FFR) reflects alterations in intracellular calcium cycling during changing heart rate (HR). Tachycardia-induced heart failure is associated with depletion of intracellular calcium. We hypothesized (1) that the relative resistance to tachycardia-induced heart failure seen in neonatal pigs is related to differences in calcium cycling, resulting in different FFR responses and (2) that pretreatment with digoxin to increase intracellular calcium would modifies these changes. LV +dP/dt was measured during incremental right atrial pacing in 16 neonatal and 14 adult pigs. FFR was measured as the change in +dP/dt as HR was increased. Animals were randomized to control or intravenous bolus digoxin (n = 8 neonate pigs in the 0.05 mg/kg group and n = 7 adult pigs in the 0.025 mg/kg group) and paced for 90 min at 25 bpm greater than the rate of peak +dP/dt. Repeat FFR was then obtained. The postpacing FFR in neonatal control pigs shifted rightward, with peak force occurring 30 bpm greater than baseline (P < 0.03). There was no vertical shift; thus, force at 150 bpm decreased (P < 0.03) and force at 300 beats/min increased (P < 0.08). In adult control pigs, FFR shifted downward (P < 0.01), with decreased force generation at all HRs. In both neonates and adult pigs, digoxin increased +dP/dt at all HRs; however, in neonate pigs digoxin decreased the contractile reserve by abrogation of the rightward shift of FFR. An adaptive response to tachycardia in the neonate pig leads to improved force generation at greater HRs. Conversely, the response of the mature pig heart is maladaptive with decreased force generation. Pretreatment with digoxin modifies these responses.

The effect of weight training on bone mineral density and bone turnover in postmenopausal breast cancer survivors with bone loss: a 24-month randomized controlled trial

SUMMARY

This study examined whether 24 months of weight training exercises enhanced the effectiveness of risedronate, calcium, and vitamin D in maintaining or improving bone mineral density (BMD) in 223 postmenopausal breast cancer survivors. Subjects who were > or =50% adherent to exercise had no improvement in BMD but were less likely to lose BMD.

INTRODUCTION

This study examined whether (1) postmenopausal breast cancer survivors (BCS) with bone loss taking 24 months of risedronate, calcium, and vitamin D had increased bone mineral density (BMD) at the total hip, femoral neck, L1-L4 spine, total radius and 33% radius, and decreased bone turnover; (2) subjects who also participated in strength/weight training (ST) exercises had greater increases in BMD and greater decreases in bone turnover; and (3) subjects who also exercised were more likely to preserve (at least maintain) BMD.

METHODS

Postmenopausal BCS (223) were randomly assigned to exercise plus medication or medication only groups. Both groups received 24 months of 1,200 mg of calcium and 400 IU of vitamin D daily and 35 mg of risedronate weekly, and the exercise group additionally had ST exercises twice weekly.

RESULTS

After 24 months, women who took medications without exercising had significant improvements in BMD at the total hip (+1.81%) and spine (+2.85%) and significant decreases in Alkphase B (-8.7%) and serum NTx (-16.7%). Women who also exercised had additional increases in BMD at the femoral neck (+0.29%), total hip (+0.34%), spine (+0.23%), total radius (+0.30%), and additional decreases in Alkphase B (-2.4%) and Serum NTx (-6.5%). Additional changes in BMD and bone turnover with exercise were not significant. Subjects who were > or =50% adherent to exercise were less likely to lose BMD at the total hip (chi-square [1] = 4.66, p = 0.03) and femoral neck (chi-square [1] = 4.63, p = 0.03).

CONCLUSION

Strength/weight training exercises may prevent loss of BMD in postmenopausal BCS at risk for bone loss.

Opioids and myocardial reperfusion injury

It is well-established that reperfusion is the major method of salvaging ischemic myocardium following prolonged coronary artery occlusion, although the idea of reperfusion injury remains controversial. Moreover, more recent evidence strongly suggests that reperfusion per se is thought to result in further damage to the myocardium and blood vessel endothelium by various biochemical and physical factors including a burst of oxygen-derived free radicals (ROS), cellular or mitochondrial calcium overload and shear stress, to name a few. This has been termed lethal reperfusion injury. It has become increasingly evident that strategies in which interventions are administered during the early stages of reperfusion produce a reduction in reperfusion-mediated damage primarily by reducing massive calcium overload or by altering the intracellular milieu (pH, osmotic stress, etc.) and ROS release upon reperfusion. Furthermore, it is apparent that activation of blood borne elements such as neutrophils and macrophages and factors released by these cells such as cytokines may be responsible for a continuing expansion of infarction in the hours or even days following timely reflow and that inhibiting these factors may attenuate reperfusion injury. The present review will focus on the effect of endogenous and exogenous opioids on ischemic and reperfusion injury since these compounds are routinely used in the surgical arena and may have unappreciated cardioprotective effects in this subset of patients. Particular emphasis will be on the role of opioids in reperfusion injury and their relationship to the newly discovered phenomenon of postconditioning.

Impaired p38 MAPK/HSP27 signaling underlies aging-related failure in opioid-mediated cardioprotection

Cardioprotection and preconditioning mediated via G-protein-coupled receptors may be lost or impaired with advancing age, limiting ischemic tolerance and the ability to pharmacologically protect older hearts from ischemic injury. Our preliminary findings indicated a loss of delta-opioid receptor-mediated protection in aged vs. young mouse hearts, which may involve alterations in protective kinase signaling. In the present study, we tested the hypothesis that aging-related loss of opioid-triggered cardioprotection involves failure to activate p38 MAPK and its distal signaling targets. Langendorff-perfused hearts from young (10-14 weeks) or aged (24-26 months) C57 mice underwent 25-min ischemia and 45-min reperfusion in the presence or absence of 1 micromol/l DPDPE (delta-opioid agonist) or 1 micromol/l anisomycin (activator of p38 MAPK), and functional recovery and protein activation/phosphorylation were assessed. Contractile recovery was similar in untreated young and aged hearts (50+/-2% and 53+/-5%, respectively), and was enhanced by DPDPE in young hearts only (67+/-3%). Immunoblot analysis revealed that DPDPE comparably activated or phosphorylated GRK2, Akt, ERK1/2 and p70S6 kinase in young and aged hearts, whereas aging abrogated the stimulatory effects of DPDPE on p38 MAPK and HSP27. Treatment with anisomycin elicited comparable activation of p38 MAPK and HSP27 in both young and aged hearts, coupled with a pronounced and equivalent cardioprotection in the two groups (73+/-3% and 77+/-2%, respectively), an effect abolished by the p38 MAPK inhibitor, SB203580. These data indicate that aging-related loss of delta-opioid-mediated cardioprotection involves failure to activate p38 MAPK and HSP27. Direct targeting of this pathway elicits comparable protection in both age groups.

[Contribution of the endogenous opioid system to regulation of heart resistance to the arrhythmogenic effect of short-term ischemia and reperfusio]

Preliminary selective blockade of micro, delta1, delta2, kappa1, and kappa2 opioid receptors proved to have no effect on the incidence of ventricular arrhythmias during a 10-min coronary occlusion and subsequent reperfusion in ketamine-anesthetized rats. We propose that the endogenous opioid system has no considerable role in regulation of heart resistance to the arrhythmogenic effect of short-term local ischemia and subsequent reperfusion.

Cardioprotection following adenosine kinase inhibition in rat hearts

Adenosine kinase phosphorylates adenosine to AMP, the primary pathway for adenosine metabolism under basal conditions. Inhibition of adenosine kinase results in a site-specific increase in interstitial adenosine. Using a rat model of myocardial infarction, we examined the protective effects of adenosine kinase inhibition. Male Sprague-Dawley rats underwent 30 min regional occlusion followed by 90 min reperfusion. Infarct size, expressed as a percent of the area-at-risk, IS/AAR(%), was 58.0 +/- 2.1 % in untreated rats. Pretreatment with the adenosine kinase inhibitor, 5-iodotubercidin (1 mg/kg), limited infarct development to 37.5+/-3.7% (P < 0.001). The A(1) adenosine receptor (A(1)AR) antagonist, DPCPX (100 microg/kg), abolished the infarct-sparing effect of 5-iodotubercidin (IS, 62.8 +/- 1.3%). Similarly, the A(3) adenosine receptor (A(3)AR) antagonist, MRS-1523 (2 mg/kg), and the delta-opioid receptor (DOR) antagonist, BNTX, (1 mg/kg) abolished the reduction of IS produced by iodotubercidin. Pretreatment with the ROS scavenger, 2-MPG (20 mg/kg), or the PKC-delta antagonist, rottlerin (0.3 mg/kg) also abolished iodotubercidin-mediated cardioprotection. Furthermore, pretreatment with 5-HD, a mitochondrial K(ATP) (mitoK(ATP)) channel inhibitor, but not the sarcolemmal K(ATP) channel blocker, HMR-1098, abrogated the beneficial effects of adenosine kinase inhibition (IS, 59.5 +/- 3.8%). These data suggest that inhibition of adenosine kinase is effective in reducing infarct development via A(1)AR, A(3)AR and DOR activation. Data also suggest that this protection is mediated via ROS, PKC-delta and mitoK(ATP) channels.

Role of Endogenous Opioid Receptor Agonists in Regulation of Heart Resistence to the Arrhythmogenic Action of Short-Term Ischemia and Reperfusion

Preliminary selective block of mu-, delta1-, delta2-, and kappa-opioid receptors had no effect on the incidence of ventricular arrhythmias during 10-min coronary occlusion-reperfusion in ketamine-narcotized rats. Repetitive short-term immobilization of rats for 2 weeks improved heart resistance to the arrhythmogenic action of coronary occlusion and reperfusion. Selective mu-opioid receptor antagonist CTAP completely abolished, while selective delta- and kappa-opioid receptor antagonists did not modulate the antiarrhythmic effect of adaptation. Probably, endogenous agonists of mu-opioid receptors play an important role in the adaptive improvement of heart resistance to arrhythmogenic factors, but are insignificant for the modulation of heart resistance to the arrhythmogenic action of short-term local ischemia-reperfusion in non-adapted animals.

[Endogenic opioid peptides and antiarrhythmic effect of adaptation to stress]

Adaptation of rats to repeated short-term immobilization increases cardiac resistance to an arrhythmogenic action of coronary artery occlusion (10 min) and reperfusion (10 min) in rats anesthetized with ketamine and artificially ventilated. We examined the role of opioid receptors and endogenous opioid peptides in the development of this antiarrhythmic effect produced in response to repeated periods of immobilization stress. We found that repeated daily stress during a 15-day period resulted in an increase of leu-enkephalin in blood plasma, in the suprarenal gland and myocardium. Adaptation to stress also resulted in an increase in beta-endorphinl-31 in blood plasma, the hypophysis, hypothalamus and midbrain. Pretreatment with selective mu, delta and cappa opioid receptor (OR) antagonists had no effect on the incidence of occlusion and reperfusion-induced arrhythmias in non-adapted control rats. However, pretreatment with the selective muOR antagonist CTAP (0.5 mg/kg) intravenously completely abrogated the antiarrhythmic effect of adaptation. Selective delta and cappa receptor antagonists did not affect the antiarrhythmic effect of adaptation. Prior administration of the selective muOR agonist DALDA (0.1 mg/kg) decreased the incidence of occlusion and reperfusion-evoked arrhythmias in non-adapted rats. This effect was abolished by pretreatment with the selective muOR antagonist CTAP (0.5 mg/kg). These data suggest that mu opioid receptors and endogenous opioid peptides play an important role in the antiarrhythmic effect of adaptation to stress in rats.

[Antiarrhythmic and cardioprotective effect of stimulation of delta1-opiate receptors in myocardial ischemia and reperfusion]

Pretreatment with intravenous peptide delta1-opioid receptor (OR) agonist DPDPE (0.5 mg/kg) decreases the incidence of occlusion (10 min) and reperfusion (10 min) arrhythmias in rats. The agonist of delta2-OR DSLET has no effect on arrhythmias in coronary artery occlusion and reperfusion. Pretreatment with selective delta-antagonists ICI 174,864 (2.5 mg/kg) eliminates an antiarrhythmic effect of DPDPE. The addition of DPDPE to the perfusion solution in a final concentration of 0.1 mg/l and/or 0.5 mg/l fifteen min before ischemia also decreases the incidence of reperfusion arrhythmias in a concentration-dependent manner. The addition of DPDPE to the perfusion solution in a final concentration of 0.1 mg/l decreases creatine kinase levels in the coronary sinus effluent. However, DPDPE has no cardioprotective effect in a concentration of 0.5 mg/l or after intravenous administration. It is suggested that antiarrhythmic and cardioprotective effects of DPDPE during reperfusion may be due to stimulation of cardiac delta1-receptors.

[The effect of K(ATP)-channel activation on the electrical stability of myocardium in rats with postinfarction cardiosclerosis]

Opening of the ATP-dependent K-channels (K(ATP) channels) upon intravenous administration of the cardioselective activator BMS 180448 (3 mg/kg) decreased the ventricular fibrillation threshold (VFT) in rats with postinfarction cardiosclerosis (PIC). Preliminary injection of the selective K(ATP) channel blocker glibenclamide (0.3 mg/kg, i.v.) completely abolished the profibrillatory effect of BMS 180448. At the same time, the mitochondrial K(ATP) channel blocker 5-hydroxydecanoic acid (5 mg/kg) did not influence the proarrhythmogen activity of BMS 180448. Simultaneous administration of the sarcoK(ATP) channel inhibitor HMR 1098 (3 mg/kg) and BMS 180448 increased the VFT up to a level in intact animals. Administration of the mitoK(ATP) channel activator diazoxide (5 mg/kg) after preliminary treatment with guanethidine (50 mg/kg) increased the VFT in rats with PIC. It is concluded that opening of the mitoK(ATP) channels increases the cardiac electrical stability in rats with PIC.

[The role of delta-1 opiate receptors in regulation of contractility in isolated rat heart during normal oxygenation and ischemia-reperfusion]

The experiments on isolated rat heart demonstrated significant decrease in reperfusion-induced damage of cardiomyocytes by addition of selective delta 1 receptor agonist DPDPE (0.1 mg/l) to the perfusion solution. On the contrary, no cardioprotective effect was observed for 0.5 mg/l concentration of the peptide or after its intravenous injection. Stimulation of the cardiac delta 1 opioid receptors by intravenous injection of 0.5 mg/kg DPDPE or its addition to the perfusion solution decreased myocardial contractility both in conditions of normal oxygenation and during reperfusion. Thus, the cardioprotective and negative inotropic effect of DPDPE is mediated by activation of the cardiac delta 1 opioid receptors.

Anandamide content is increased and CB1 cannabinoid receptor blockade is protective during transient, focal cerebral ischemia

The role of endocannabinoid signaling in the response of the brain to injury is tantalizing but not clear. In this study, transient middle cerebral artery occlusion (MCAo) was used to produce ischemia/reperfusion injury. Brain content of N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol were determined during MCAo. Whole brain AEA content was significantly increased after 30, 60 and 120 min MCAo compared with sham-operated brain. The increase in AEA was localized to the ischemic hemisphere after 30 min MCAo, but at 60 and 120 min, was also increased in the contralateral hemisphere. 2-Arachidonoylglycerol content was unaffected by MCAo. In a second set of studies, injury was assessed 24 h after 2 h MCAo. Rats administered a single dose (3 mg/kg) of the cannabinoid receptor type 1 (CB1) receptor antagonist SR141716 prior to MCAo exhibited a 50% reduction in infarct volume and a 40% improvement in neurological function compared with vehicle control. A second CB1 receptor antagonist, LY320135 (6 mg/kg), also significantly improved neurological function. The CB1 receptor agonist, WIN 55212-2 (0.1-1 mg/kg) did not affect either infarct volume or neurological score.

[The role of opiate receptors and ATP-dependent potassium channels of mitochondria in the formation of myocardial adaptive resistance to the arrhythmogenic effect of ischemia and reperfusion]

Preliminary stimulation of opiate receptors (ORs) by intravenous administration of mu agonist DALDA (0.5 mg/kg), delta 1 agonist DPDPE (0.5 mg/kg), and kappa agonist (-)-U-50.488 (1 mg/kg) increases rat myocardial resistance to arrhythmogenic effect of coronary occlusion (10 min) and reperfusion (10 min). Activation of delta 2 ORs (DSLET, 0.5 mg/kg) has no effect on the incidence rate of ischemic and reperfusion arrhythmias. Preliminary administration of glibenclamide (0.3 mg/kg), an inhibitor of KATP channels, blocks the antiarrhythmic effect of DALDA and DPDPE. Repeated short-term exposures of rats to immobilization within two weeks increases the heart tolerance to the arrhythmogenic effect of coronary occlusion and reperfusion. This effect disappears after administration of CTAP (0.5 mg/kg), a mu antagonist, or injection of 5-hydroxydecanoate (5 mg/kg), an inhibitor of mitochondrial KATP channels. The selective antagonists of delta and kappa ORs have no effect on cardiac adaptation-induced resistance to the arrhythmogenic effect of ischemia and reperfusion. We believe that stimulation of mu, delta, and kappa ORs increases myocardial tolerance to the arrhythmogenic effect of ischemia and reperfusion through activation of KATP channels. The antiarrhythmic effect of the adaptation is mediated by stimulation of mu ORs and mitochondrial KATP channels.

Activation of peripheral delta opioid receptors eliminates cardiac electrical instability in a rat model of post-infarction cardiosclerosis via mitochondrial ATP-dependent K+ channels

The effects of the selective delta-1 (delta(1)) opioid receptor agonist, DPDPE, and the selective delta(2) opioid receptor agonist, DSLET, have been studied on the ventricular fibrillation threshold (VFT) in rats with an experimental post-infarction cardiosclerosis (CS). It has been found that CS induced a significant decrease in VFT. This CS-induced decrease in VFT was significantly reversed by intravenous administration of DPDPE (0.1 mg/kg) 10 min before VFT measurement. On the contrary, intravenous injection of DSLET (0.5 mg/kg) exacerbated the CS-induced cardiac electrical instability. Pretreatment with the selective delta opioid receptor antagonist, ICI 174,864 (0.5 mg/kg), completely abolished the changes in VFT produced by both DPDPE and DSLET. Previous administration of a nonselective peripherally acting opioid receptor antagonist, naloxone methiodide (5 mg/kg) also completely reversed the antifibrillatory action of DPDPE. Naloxone methiodide and ICI 174,864 alone had no effect on VFT. Pretreatment with the nonselective K(ATP) channel blocker, glibenclamide (0.3 mg/kg), or with the mitochondrial selective K(ATP) channel blocker, 5-hydroxydecanoic acid (5-HD, 5 mg/kg), completely abolished the DPDPE-induced increase in cardiac electrical stability. Glibenclamide and 5-HD alone had no effect on VFT. These results demonstrate that the delta opioid receptor plays an important role in the regulation of electrical stability in rats with post-infarction cardiosclerosis. We propose that peripheral delta(1) opioid receptor stimulation reverses CS-induced electrical instability via mitochondrial K(ATP) channels. On the contrary, delta(2) opioid receptor stimulation may exacerbate the CS-induced decrease in VFT. Further studies are necessary to determine the delta opioid receptor subtype which mediates the antifibrillatory effect of DPDPE and pro-fibrillatory effect of DSLET.

[The opiatergic link between the antiarrhythmic effect of adaptation and hypoxia in the model of ischemia and reperfusion in vivo]

Rat adaptation to repeated periods of hypobaric hypoxia has been found to prevent the occurrence of ischemic and reperfusion ventricular arrhythmias on a 10-minte coronary artery occlusion model. Inhibition of delta-opioid receptors by intravenous administration of the selective delta-opioid antagonist TIPP (psi) in a dose of 0.5 mg/kg, intravenously (i.v.), completely abolished the antiarrhythmic effect of adaptation to hypoxia. Inhibition of mu-opioid receptors by CTAP (0.5 mg/kg, i.v.) or kappa-receptors by nor-binaltorphimine (9 mg/kg i.v.) had no effect on the incidence cardiac rhythm disturbances in adapted rats during coronary artery occlusion and reperfusion. Therefore, these findings suggest that delta-opioid receptors play an important role in inhibiting arrhythmia formation in this model.

Sarcolemmal and mitochondrial K(ATP) channels and myocardial ischemic preconditioning

Ischemic preconditioning (IPC) is the phenomenon whereby brief periods of ischemia have been shown to protect the myocardium against a sustained ischemic insult. The result of IPC may be manifest as a marked reduction in infarct size, myocardial stunning, or incidence of arrhythmias. While many substances and pathways have been proposed to play a role in the signal transduction mediating the cardioprotective effect of IPC, overwhelming evidence indicates an intimate involvement of the ATP-sensitive potassium channel (K(ATP) channel) in this process. Initial hypotheses suggested that the surface or sarcolemmal K(ATP) (sarcK(ATP)) channel mediated the cardioprotective effects of IPC. However, much research has subsequently supported a major role for the mitochondrial K(ATP) channel (mitoK(ATP)) as the one involved in IPC-mediated cardioprotection. This review presents evidence to support a role for the sarcK(ATP) or the mitoK(ATP) channel as either triggers and/or downstream mediators in the phenomenon of IPC.

Effect of in vivo and in vitro stimulation of delta1-opioid receptors on myocardial resistance to arrhythmogenic action of ischemia and reperfusion

Preliminary intravenous injection of peptide agonist of delta1-opioid receptors DPDPE (0.5 mg/kg) decreased the incidence of occlusion (10 min) and reperfusion (10 min) arrhythmias in rats. By contrast, delta2-opioid receptor agonist DSLET produced no effect on the incidence of arrhythmias provoked by coronary occlusion and reperfusion. Preliminary injection of selective delta-receptor antagonist ICI 174,864 (2.5 mg/kg) or TIPP[y] (0.5 mg/kg) completely abolished the antiarrhythmic effect of DPDPE. Stimulation of cardiac delta1-opioid receptors with DPDPE added to perfusion saline in concentrations of 0.1 and 0.5 mg/liter decreased the incidence of reperfusion arrhythmias. Addition of DPDPE to perfusion saline in a concentration of 0.1 mg/liter prevented reoxygenation destruction of cardiomyocytes. By contrast, no cardioprotective effect of this peptide was observed at a concentration of 0.5 mg/liter in perfusion saline or when it was injected intravenously. It is concluded that the cardioprotective and antiarrhythmic effects of DPDPE are caused by activation of cardiac delta1-opioid receptors.

Predictors of refractory tachycardia in infants with supraventricular tachycardia

Reentrant supraventricular tachycardia (SVT) is the most common arrhythmia in infants. There are few predictors as to which patients will have recurrent or refractory SVT. We retrospectively reviewed records of all infants with SVT evaluated at The Hospital for Sick Children, Toronto, between January 1, 1995, and December 31, 1999. Patients with reentrant SVT documented in infancy and structurally normal hearts were included. Patients were placed in two groups: the "simple" group consisted of patients with SVT completely controlled by not more than one medication, and the "complex" group consisted of patients with recurrent episodes requiring at least one medication change for control. Forty-two cases were analyzed-23 in the simple group and 19 in the complex group. One patient in each group died. Age at presentation was 50.4 +/- 13.2 days for the simple group versus 10.2 +/- 2.5 days for the complex group (p <0.01). Complex patients were treated with a median of three medications and were more likely to have echocardiographically reduced ventricular function. The surface electrocardiogram RP interval during SVT was significantly longer in complex patients (p <0.001). There were no differences between the groups in gender, cycle length in SVT or sinus rhythm, the presence of pre-excitation, initial medication choice, or duration of therapy. Recurrent SVT in infancy is associated with younger age and/or ventricular dysfunction at presentation and also with slower ventriculoatrial conduction. The similar duration of therapy for simple and complex patients suggests that the early clinical course of SVT in infancy is not predictive of long-term outcome.

[Interactions of peripheral mu-opioid receptors and K(ATP)-channels in regulation of cardiac electrical stability in ischemia, reperfusion, and postinfarction cardiosclerosis]

It has been shown that mu-opioid receptor stimulation by intravenous administration of the selective mu receptor agonist DALDA in a dose of 0.1 mg/kg prevented ischemic and reperfusion arrhythmias in rats subjected to coronary artery occlusion (10 min) and reperfusion (10 min), and also increased the ventricular fibrillation threshold in rats with postinfarction cardiac fibrosis. These effects were abolished by pre-treatment with the selective mu receptor antagonist CTAP in a dose of 0.5 mg/kg or by prior injection of the opioid receptor antagonist naloxone methiodide (2 mg/kg) which does not penetrate the blood-braib barrier. Both antagonists by themselves had no effect on the incidence of occlusion or reperfusion-induced arrhythmias or on the ventricular fibrillation threshold. Pre-treatment with ATP-sensitive K+ channel (KATP channel) blocker glibenclamide in a dose of 0.3 mg/kg completely abolished the antiarrhythmic effect of DALDA. We believe that DALDA prevents occurrence of electrical instability during ischemia and reperfusion and increases the ventricular fibrillation threshold in rats with postinfarction cardiac fibrosis via stimulation of peripheral mu-opioid receptor which appear to be coupled to the KATP channel.

Receptor specificity of the antiarrhythmic effect produced by opioid peptides Dalargin and DADLE during myocardial reperfusion

Nonselective agonists of mu- and delta-opioid receptors dalargin (D-Ala2,Leu5,Arg6-enkephalin) and DADLE (D-Ala2,D-Leu5-enkephalin) administered immediately before coronary reperfusion in a dose of 0.1 mg/kg prevented the development of ventricular arrhythmias. Blockade of mu-opioid receptors abolished the antiarrhythmic effect of these peptides. Hence, antiarrhythmic activity of dalargin and DADLE is primarily associated with activation of mu-opioid receptors.

Mothers' Decision‐Making Processes Regarding Health Care for Their Children

This research study explored mothers' decision-making processes regarding health care for their children. Identifying how decisions are made by mothers about health care for their children will assist health care professionals to be appropriate advocates for mothers, to improve quality of life, and to contain costs of health care for children. A sample of 114 rural mothers (51 with one child, 63 with more than one child) completed questionnaires identifying demographics, social support, client and professional interaction elements, self-determinism, competence in problem-solving skills, and relationships to responses to health care scenarios. Qualitative data were also gathered by structured in-depth interviews of 7 subjects. ANOVA, correlations, and factor analysis were completed to analyze data. Most of the mothers' decisions were based on the perceived degree of seriousness, mother's degree of fear of the child's condition, attitude of the health care provider, previous experience with the situation, and social support for the mother. There were no significant differences in decision-making processes by first time mothers and by mothers with more than one child. Implications include teaching mothers assessment skills to identify serious versus nonserious situations and to utilize other social supports.

Characteristics and superoxide-induced activation of reconstituted myocardial mitochondrial ATP-sensitive potassium channels

Mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels have been suggested as triggers and end effectors in myocardial ischemic preconditioning. However, the intracellular mechanism regulating mitoK(ATP) channels remains unclear. In the present study, mitoK(ATP) channels from bovine ventricular myocardium were reconstituted using planar lipid bilayers, and the effect of superoxide (O(2-.)) on the activity of these reconstituted channels was examined. After incorporation, a potassium-selective current was recorded. The mean conductance of this current was 56 pS at 150 mmol/L KCl, which was substantially inhibited by 1 mmol/L MgATP. 5-Hydroxydecanoate (5-HD, 10 to 100 micromol/L), a selective mitoK(ATP) antagonist, reduced the open state probability (NPo) of these channels in a concentration-dependent manner, whereas diazoxide (10 micromol/L), a selective mitoK(ATP) agonist, significantly increased channel activity. HMR-1098 (100 micromol/L), a selective sarcolemmal K(ATP) antagonist, had no effect on the activity of reconstituted channels. Addition of xanthine/xanthine oxidase (100 micromol/L per 0.038 U/mL), an O(2-.)-generating system, resulted in a marked activation of mitoK(ATP) channels; the NPo of the channels was increased from 0.60+/-0.10 to 1.94+/-0.02. This O(2)(-.)-induced channel activation was completely abolished by pretreatment with 5-HD (100 micromol/L) or a sulfhydryl alkylating compound, N-ethylmaleimide (2 mmol/L). It is concluded that myocardial mitoK(ATP) channels can be reconstituted into lipid bilayers and that O(2-.) activates these channels. The effect of O(2-.) may be associated with its direct action on the sulfhydryl groups of the channel protein.

Blocking Na(+)/H(+) exchange reduces [Na(+)](i) and [Ca(2+)](i) load after ischemia and improves function in intact hearts

We determined in intact hearts whether inhibition of Na(+)/H(+) exchange (NHE) decreases intracellular Na(+) and Ca(2+) during ischemia and reperfusion, improves function during reperfusion, and reduces infarct size. Guinea pig isolated hearts were perfused with Krebs-Ringer solution at 37 degrees C. Left ventricular (LV) free wall intracellular Na(+) concentration ([Na(+)](i)) and intracellular Ca(2+) concentration ([Ca(2+)](i)) were measured using fluorescence dyes. Hearts were exposed to 30 min of ischemia with or without 10 microM of benzamide (BIIB-513), a selective NHE-1 inhibitor, infused for 10 min just before ischemia or for 10 min immediately on reperfusion. At 2 min of reperfusion, BIIB-513 given before ischemia decreased peak increases in [Na(+)](i) and [Ca(2+)](i), respectively, from 2.5 and 2.3 times (controls) to 1.6 and 1.3 times pre-ischemia values. At 30 min of reperfusion, BIIB-513 increased systolic-diastolic LV pressure (LVP) from 49 +/- 2% (controls) to 80 +/- 2% of pre-ischemia values. BIIB-513 reduced ventricular fibrillation by 54% and reduced infarct size from 64 +/- 1% to 20 +/- 3%. First derivative of the LVP, O(2) consumption, and cardiac efficiency were also improved by BIIB-513. Similar results were obtained with BIIB-513 given on reperfusion. These data show that Na(+) loading is a marker of reperfusion injury in intact hearts in that inhibiting NHE reduces Na(+) and Ca(2+) loading during reperfusion while improving function. These results clearly implicate the ionic basis by which inhibiting NHE protects the guinea pig intact heart from ischemia-reperfusion injury.

Spontaneously terminating apparent ventricular fibrillation during transesophageal electrophysiological testing in infants with Wolff-Parkinson-White syndrome

This article describes two infants with Wolff-Parkinson-White (WPW) syndrome in whom apparent VF occurred without antecedent AF or atrial flutter during routine transesophageal electrophysiological testing. Remarkably, this arrhythmia terminated spontaneously in both infants. The documentation of self-limited apparent VF, or polymorphic ventricular tachycardia close to VF, in transesophageal testing adds another dimension to the management of WPW.

[Role of delta opioid receptors and their ligands in the development of adaptive heart protection against arrhythmogenesis]

It has been found that stimulation of delta-1 opioid receptors by intravenous administration of DPDPE (0.5 mg/kg) decreases the incidence of ischemic and reperfusion-induced arrhythmias and also increases myocardial tolerance to the arrhythmogenic action of epinephrine in rats. Pretreatment with a selective delta-2 agonist, DSLET, had no antiarrhythmic effect. The inhibition of the enzymatic breakdown of endogenous enkephalins by intravenous administration of acetorphan decreased the incidence of epinephrine-induced arrhythmias. Pretreatment with a selective delta opioid receptor antagonist, ICI-174.868, completely abolished this antiarrhythmic effect. Adaptation of rats to repeated immobilization stress during 12 days increased myocardial tolerance to the arrhythmogenic action of coronary artery occlusion (10 min) and reperfusion (10 min). Pretreatment with a selective delta opioid receptor antagonist, TIPP(Psy), did not abolish the antiarrhythmic effect of adaptation to immobilization stress. It seems that endogenous agonists of delta opioid receptors are not involved in the antiarrhythmic effect resulting from adaptation to stress.

Dependence of delta1-opioid receptor-induced cardioprotection on a tyrosine kinase-dependent but not a Src-dependent pathway

We investigated the possibility that opioids activate a tyrosine kinase (TK) that mediates cardioprotection in an in vivo rat model of myocardial infarction. All animals underwent 30 min of regional ischemia and 2 h of reperfusion. Infarct size was expressed as a percentage of the area at risk (IS/AAR). Control animals had an IS/AAR of 58.2 +/- 0.6. Cardioprotection was induced with the delta1- or delta1/delta2-selective opioid agonists, TAN-67, or D-Ala D-Leu enkephalin (DADLE). Both significantly reduced IS/AAR (28.8 +/- 3.6 and 34.8 +/- 3.8, respectively). The general TK inhibitor, genistein, abolished cardioprotection produced by TAN-67 or DADLE (59.1 +/- 3.2 and 61.5 +/- 3.4, respectively), whereas the structural analog, daidzein, lacking TK inhibitory activity, did not. Interestingly, the selective Src/epidermal growth factor (EGF) receptor TK inhibitor, lavendustin A, did not abolish TAN-67-induced cardioprotection (22.1 +/- 6.8). Similarly, the Src-selective TK antagonist, PP2, had no effect on DADLE-induced cardioprotection (31.1 +/- 7.3). These unexpected findings suggest that Src and EGF receptor TKs are not important in the genesis of cardioprotection produced by TAN-67. Finally, we demonstrate that genistein did not affect protein kinase C (PKC) translocation induced by TAN-67. These data suggest that a TK, but most likely not an Src/EGF receptor TK, is important in cardioprotection via opioid receptor stimulation and that the pathway for TK activation is downstream from or parallel to PKC activation in the in situ rat heart since genistein could not affect PKC translocation of selective isoforms induced by TAN-67 and assessed by immunohistochemistry.

[Stimulation of peripheral delta1-opioid receptors as a method of preventing ischemic and reperfusion arrhythmia: role of K(ATP)-channels]

Preliminary administration of the delta 1-opioid receptor (delta 1-OR) peptide agonist DPDPE (0.5 mg/kg, i.v.) decreased the incidence of occlusion (10 min) and reperfusion (10 min) arrhythmias in rats. The delta 2-OR agonist DSLET did not affect arrhythmias upon the coronary artery occlusion and reperfusion. Pretreatment with the selective delta-antagonists ICI 174,864 (2.5 mg/kg) or TIPP[psi] (0.5 mg/kg) completely eliminated the antiarrhythmic effect of DPDPE. Uncapable of crossing the blood brain barrier, the nonselective OR antagonist naloxone methiodide (5 mg/kg) also abolished this effect. At the same time, hexametonium (10 mg/kg) did not antagonize the antiarrhythmic effect of DPDPE. Pretreatment with the KATP channel blocker glibenclamide (0.3 mg/kg) completely eliminated the protective effect of the delta 1-OR stimulation. It was concluded that the delta 1-OR stimulation prevents the ischemic and reperfusion arrhythmias by means of the KATP channel activation.

Stress-activated protein kinase phosphorylation during cardioprotection in the ischemic myocardium

Stress-activated protein kinases may be essential to cardioprotection. We assessed the role of p38 in an in vivo rat model of ischemia-reperfusion. Ischemic preconditioning (IPC) and the delta(1)-opioid receptor agonist 2-methyl-4aalpha-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12aalpha-octahydroquinolino [2,3,3-g]isoquinoline (TAN-67) significantly reduced infarct size (IS), expressed as a percentage of the area at risk (AAR), versus animals subjected only to 30 min of ischemia and 2 h of reperfusion (7.1 +/- 1.5 and 29.6 +/- 3.3 vs. 59.7 +/- 1.6%). The p38 antagonist SB-203580 attenuated IPC when it was administered before (34.0 +/- 6.9%) or after (25.0 +/- 3.8%) the IPC stimulus; however, it did not significantly attenuate TAN-67-induced cardioprotection (39.6 +/- 3.2). We also assessed the phosphorylation of p38 and c-jun NH(2)-terminal kinase (JNK) throughout ischemia-reperfusion in nuclear and cytosolic fractions. After either intervention, no increase was detected in the phosphorylation state of either enzyme in the nuclear fraction or for p38 in the cytosolic fraction versus control hearts. However, there was a robust increase in JNK activity in the cytosolic fraction immediately on reperfusion that was more pronounced in animals subjected to IPC or administered TAN-67. These data suggest that SB-203580 likely attenuates IPC via the inhibition of kinases other than p38, which may include JNK. The data also suggest that activation of JNK during early reperfusion may be an important component of cardioprotection.

Inhibition of Na+/Ca2+ exchange by KB-R7943: transport mode selectivity and antiarrhythmic consequences

The Na+/Ca2+ exchanger plays a prominent role in regulating intracellular Ca2+ levels in cardiac myocytes and can serve as both a Ca2+ influx and efflux pathway. A novel inhibitor, KB-R7943, has been reported to selectively inhibit the reverse mode (i.e., Ca2+ entry) of Na+/Ca2+ exchange transport, although many aspects of its inhibitory properties remain controversial. We evaluated the inhibitory effects of KB-R7943 on Na+/Ca2+ exchange currents using the giant excised patch-clamp technique. Membrane patches were obtained from Xenopus laevis oocytes expressing the cloned cardiac Na+/Ca2+ exchanger NCX1.1, and outward, inward, and combined inward-outward currents were studied. KB-R7943 preferentially inhibited outward (i.e., reverse) Na+/Ca2+ exchange currents. The inhibitory mechanism consists of direct effects on the transport machinery of the exchanger, with additional influences on ionic regulatory properties. Competitive interactions between KB-R7943 and the transported ions were not observed. The antiarrhythmic effects of KB-R7943 were then evaluated in an ischemia-reperfusion model of cardiac injury in Langendorff-perfused whole rabbit hearts using electrocardiography and measurements of left ventricular pressure. When 3 microM KB-R7943 was applied for 10 min before a 30-min global ischemic period, ventricular arrhythmias (tachycardia and fibrillation) associated with both ischemia and reperfusion were almost completely suppressed. The observed electrophysiological profile of KB-R7943 and its protective effects on ischemia-reperfusion-induced ventricular arrhythmias support the notion of a prominent role of Ca2+ entry via reverse Na+/Ca2+ exchange in this process.

Na(+)/H(+) exchange inhibition prevents endothelial dysfunction after I/R injury

Whereas inhibition of the Na(+)/H(+) exchanger (NHE) has been demonstrated to reduce myocardial infarct size in response to ischemia-reperfusion injury, the ability of NHE inhibition to preserve endothelial cell function has not been examined. This study examined whether NHE inhibition could preserve endothelial cell function after 90 min of regional ischemia and 180 min of reperfusion and compared this inhibition with ischemic preconditioning (IPC). In a canine model either IPC, produced by one 5-min coronary artery occlusion (1 x 5'), or the specific NHE-1 inhibitor eniporide (EMD-96785, 3.0 mg/kg) was administered 15 min before a 90-min coronary artery occlusion followed by 3 h of reperfusion. Infarct size (IS) was determined by 2,3,5-triphenyl tetrazolium chloride staining and expressed as a percentage of the area-at-risk (IS/AAR). Endothelial cell function was assessed by measurement of coronary blood flow in response to intracoronary acetylcholine infusion at the end of reperfusion. Whereas neither control nor IPC-treated animals exhibited a significant reduction in IS/AAR or preservation of endothelial cell function, animals treated with the NHE inhibitor eniporide showed a marked reduction in IS/AAR and a significantly preserved endothelial cell function (P < 0.05). Thus NHE-1 inhibition is more efficacious than IPC at reducing IS/AAR and at preserving endothelial cell function in dogs.

[Participation of K(ATP)-channels in cardioprotective effect of mu-opioid receptor agonists in acute ischemia and reperfusion of the isolated heart]

Preliminary administration of the mu-opioid receptor (mu-OR) agonist DAMGO (0.1 mg/kg) 15 min before heart isolation led to attenuation of the postischemic systolic and diastolic contractility dysfunction in isolated perfused rat heart. In addition, the mu-OR decreased creatine kinase (CK) release from the heart during the postischemic period, which was indicative of an increase in the sarcolemma tolerance to reperfusion injury. This protective effects are mediated by KATP channel activation. These data show that the mu-OR stimulation in vivo increases, by means of the KATP channel activation, the cardiac tolerance to the ischemia and reperfusion injury in vitro. Pretreatment with mu-OR agonists DAMGO or DALDA in vitro (0.5 mg/liter, 15 min prior to ischemia) exacerbated the postischemic contractility dysfunction of myocardium and did not affect the CK release. It is concluded that the protective effect of mu-OR simulation in vivo is mediated by the activation of these receptors localized outside the heart, probably with an unknown circulating humoral factor.

Transient outward current inhibition by propafenone and 5-hydroxypropafenone in cultured neonatal rat ventricular myocytes

The antiarrhythmic agent propafenone and its primary electropharmacologically active metabolite, 5-hydroxypropafenone, are known inhibitors of cardiac myocyte repolarizing currents. We recently documented potent propafenone inhibition of the transient outward potassium current (Ito) in human atrial myocytes from patients in the newborn and infant age range. In the current study we characterized ventricular Ito inhibition by propafenone and 5-hydroxypropafenone in neonatal myocytes enzymatically isolated from 2-day-old Sprague-Dawley rat pups. Using the whole-cell patch-clamp technique in ventricular myocytes kept in primary culture for 1-4 days, we observed comparably potent Ito inhibition by both agents, yielding 50% maximal inhibitory concentration (IC50) values of 2.1 +/- 0.5 and 1.5 +/- 0.2 microM for propafenone and 5-hydroxypropafenone, respectively. Ito blockade by both of these agents was time, concentration, and voltage dependent, but use independent. There was no drug effect on steady-state voltage dependence of Ito inactivation, or on the time course of Ito recovery from inactivation. These findings are consistent with an open channel-blocking mechanism as suggested by other models. We conclude that both propafenone and 5-hydroxypropafenone are potent Ito inhibitors in neonatal rat ventricular myocytes, with potencies exceeding those demonstrated for propafenone in adult rat ventricular myocytes or in human atrial myocytes from patients of all ages.

BW373U86, a delta opioid agonist, partially mediates delayed cardioprotection via a free radical mechanism that is independent of opioid receptor stimulation

Opioids have been shown to produce both an early and delayed phase of cardioprotection; however, the signaling pathways involved, particularly in the delayed response, have not been well defined. Therefore, we investigated the potential of BW373U86 (BW), a potent delta opioid agonist, to produce delayed cardioprotection and characterized the role of opioid receptors and oxygen-derived free radicals (OFRs) in this delayed response. All rats underwent 30 min of ischemia followed by 2 h of reperfusion. The rats were divided into four groups. First, rats were pretreated with selective opioid receptor antagonists or the antioxidant, 2-mercaptopropionyl glycine (2-MPG), in the presence of BW and allowed to recover for 24 h before the ischemia-reperfusion protocol. Second, rats were pretreated with BW, allowed to recover for 24 h, and subsequently treated with either opioid antagonists or 2-MPG, 10 min prior to the ischemia-reperfusion protocol. Third, rats underwent ischemic preconditioning (IPC) (1x5 min occlusion) both with and without 2-MPG to determine the role of OFRs in acute cardioprotection. Fourth, rats were pretreated with TAN-67, an opioid agonist known to signal through the delta1 opioid receptor in the presence and absence of 2-MPG. Control rats were injected with saline and allowed to recover for 24 h. BW produced a bell-shaped dose-related reduction in infarct size with a maximal reduction observed at 0.1 mg/kg v control (16+/-3%v 60+/-3%, P<0.001). Surprisingly, the delayed protection induced by BW was only partially blocked by pretreatment with the delta1-selective antagonist, BNTX; however, it was completely blocked by pretreatment with 2-MPG (47+/-5%, P<0.001). Only naloxone given acutely inhibited the protective effects of BW; however, at the dose used, 2-MPG partially reduced the protective effect of acute IPC. TAN-67 (0.1 mg/kg) also produced a significant reduction in infarct size compared to control (18+/-4%v 60+/-3%, P<0.001). This protection was blocked by pretreatment with 2-MPG (42+/-4%, P<0.001). These data suggest that BW and TAN-67 mediate delayed cardioprotection via a free radical mechanism that appears to be only partially dependent on delta opioid receptor stimulation. Furthermore, it is the early burst in OFRs that is crucial to initiating the protective effect.

Bone mineral density in postmenopausal breast cancer survivors

PURPOSE

The overall purpose of this longitudinal 18-month study was to test the feasibility and effectiveness of a multicomponent intervention for prevention and treatment of osteoporosis. The purpose of this article is to describe the baseline bone mineral density (BMD) findings for 30 postmenopausal women and to compare these BMD findings to time since menopause, body mass index, and tamoxifen use.

DATA SOURCES

Baseline data of BMD findings for 30 postmenopausal women, who have had a variety of treatments including surgery, adjuvant chemotherapy and or tamoxifen, and are enrolled in the 18-month longitudinal study. A demographic questionnaire and a three day dietary record were used to collect baseline data.

CONCLUSIONS

Eighty percent of the women with breast cancer history had abnormal BMDs at baseline (t-scores below -1.00 SD). Thinner women showed a greater risk for accelerated trabecular bone loss at the spine and hip.

IMPLICATIONS FOR PRACTICE

These findings suggest the need for early BMD assessments and for aggressive health promotion intervention strategies that include a multifaceted protocol of drug therapy for bone remodeling, 1500 mg of daily calcium, 400 IU vitamin D and a strength weight training program that is implemented immediately following chemotherapy treatment and menopause in this high risk population of women.

Sarcolemmal and mitochondrial K(atp)channels mediate cardioprotection in chronically hypoxic hearts

X. Kong, J. S. Tweddell, G. J. Gross and J. E. Baker. Sarcolemmal and Mitochondrial K(ATP)Channels Mediate Cardioprotection in Chronically Hypoxic Hearts. Journal of Molecular and Cellular Cardiology (2001) 33, 1041-1045. Hypoxia from birth increases the resistance of the isolated neonatal heart to ischemia. We determined if increased resistance to ischemia was due to activation of sarcolemmal or mitochondrial K(ATP)channels. Rabbits (n=8/group) were raised from birth in a normoxic (F(I)O(2)=0.21) or hypoxic (F(I)O(2)=0.12) environment for 8-10 days and the heart perfused with Krebs-Henseleit bicarbonate buffer. A mitochondrial-selective K(ATP)channel blocker 5-hydroxydecanoate (5-HD) (300 micromol/l) or a sarcolemmal-selective K(ATP)channel blocker HMR 1098 (30 micromol/l) were added alone or in combination for 20 min prior to a global ischemic period of 30 min, followed by 35 min reperfusion. Recovery of ventricular developed pressure was higher in chronically hypoxic than normoxic hearts. 5-HD and HMR 1098 partially reduced the cardioprotective effect of chronic hypoxia, but had no effect in normoxic hearts. The combination of 5-HD and HMR 1098 abolished the cardioprotective effect of chronic hypoxia. We conclude that both sarcolemmal and mitochondrial K(ATP)channels contribute to cardioprotection in the chronically hypoxic heart.

Production and metabolism of ceramide in normal and ischemic-reperfused myocardium of rats

Ceramide has been shown to be a key signaling molecule involved in the apoptotic effect of tumor necrosis factor alpha (TNF-alpha) and other cytokines. Given the importance of cytokines such as TNF-alpha in myocardial ischemia-reperfusion injury, we hypothesize that ceramide is increased during ischemia or reperfusion, and that the activity of enzymes responsible for its production or breakdown should be increased and/or decreased, respectively. Therefore, in the present study, we characterized the enzymatic activities responsible for ceramide production and metabolism in the myocardium of rats, and determined the contribution of these enzymes to altered ceramide levels during myocardial ischemia and reperfusion. The basal ceramide concentration in the myocardium of rats was 34.0 pmol/mg tissue. As determined by the conversion of 14C-sphingomyelin into ceramide and 14C-choline phosphate, both neutral (N-) and acidic (A-) SMase were detected in the myocardium, with a conversion rate of 0.09 +/- 0.008 and 0.32 +/- 0.05 nmol/min per mg protein, respectively. The activity of A-SMase (78 % of total cellular activity) was significantly higher in microsomes than in cytosol, while the activity of N-SMase was similar in both fractions. Ceramidase, a ceramide-metabolizing enzyme, was also detected in the myocardium of rats. It metabolized ceramide into sphingosine at a rate of 9.94 +/- 0.42 pmol/min per mg protein. In anesthetized rats, 30 min of ischemia had no apparent effect on ceramide concentrations in the myocardium, while 30 min of ischemia followed by 3 h of reperfusion resulted in a significant increase in ceramide by 48 %. The activities of both N- and A-SMase were reduced by 44 % and 32 %, respectively, in the myocardium subjected to ischemia followed by reperfusion, but unaltered in the ischemic myocardium. It was also found that myocardial ischemia followed by reperfusion produced a marked inhibition of ceramidase (by 29 %). These results demonstrate that the myocardium of rats expresses N- and A-SMase and ceramidase, which contribute to the production and metabolism of ceramide, respectively. Tissue ceramide concentrations increased in reperfused myocardium. These increases in ceramide were not associated with enhanced SMase activity, but rather with reduced ceramidase activity.

Cardioprotection: emerging pharmacotherapy

By the year 2020, it is predicted that acute coronary occlusion will be the major cause of death in the world. Recent advances in reperfusion therapy have substantially improved survival of patients with acute coronary syndromes. While early reperfusion reduces mortality, a time limitation exists with regard to myocardial salvage. In fact, the major limiting factor in further improving survival of patients with myocardial ischaemia is the susceptibility of the cardiomyocyte to ischaemic insult and lethal cell injury. Over the last decade substantial progress has been made in our understanding of the fundamental mechanisms of ischaemia/reperfusion injury. From this work novel means which limit or delay myocyte death have emerged and are currently under development as therapeutic candidates for the management of acute coronary syndromes. This report examines cardioprotective mechanisms and reviews clinical evidence for myocardial protective therapies.

Determination of cytochrome P450 metabolites of arachidonic acid in coronary venous plasma during ischemia and reperfusion in dogs

Arachidonic acid (AA) can be metabolized by cytochrome P450 enzymes to many biologically active compounds including 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs), their corresponding dihydroxyeicosatrienoic acids (DHETs), as well as 19- and 20-hydroxyeicosatetraenoic acids (HETEs). These eicosanoids are potent regulators of vascular tone. However, their role in the ischemic myocardium has not been well investigated. In this study, we used a gas chromatographic-mass spectrometric technique to analyze total EETs, DHETs, and 20-HETE released into coronary venous plasma during coronary artery occlusion and reperfusion in anesthetized dogs. Pentafluorobenzyl esters (PFB-esters) of EETs and PFB-esters/trimethylsilyl ethers (TMS-ethers) of DHETs and 20-HETE were detected in the negative ion chemical ionization (NICI) using methane as a reagent gas. Under the conditions used, all four regioisomers of EET eluted from the capillary gas chromatographic column at similar retention times while four regioisomers of DHETs and 20-HETE eluted separately. The detection limits in plasma samples are 5 pg for total EETs, 40 pg for DHET, and 15 pg for 20-HETE. 14,15-DHET is the major regioisomer detected in the plasma samples while other regioisomers of DHETs are probably present at too low a concentration for detection. During the first 5 to 15 min of coronary occlusion, a slight decrease in the concentration of EETs, 14,15-DHET, and 20-HETE from the control values was observed in coronary venous plasma. At 60 min of occlusion, their concentrations significantly increased and remained elevated during 5 to 60 min of reperfusion. The concentrations decreased at 120 min of reperfusion. The NICI GC-MS was successfully used as a sensitive technique to determine cP450 metabolites of AA in plasma during prolonged occlusion-reperfusion periods. Furthermore, the results indicate that these metabolites may play a role in mediating ischemic-reperfusion injury.

[Effect of stimulation of mu-opiate receptors on contractility of the isolated heart in normal oxygenation and during ischemia-reperfusion]

Activation of mu-opioid receptor (OR) in rats prevented development of reperfusion-induced myocardial cell damage. In contrast, direct cardiac mu-OR stimulation with the opioid receptor agonist DAMGO decreased cardiac contractility in normal oxygenation and aggravated the reperfusion-induced myocardial cell damage. The findings suggest that the cardioprotective effect of mu-OR stimulation is not mediated via cardiac mu-OR activation.

Three-dimensional microimaging (MRmicroI and microCT), finite element modeling, and rapid prototyping provide unique insights into bone architecture in osteoporosis

With the proportion of elderly people increasing in many countries, osteoporosis has become a growing public health problem, with rising medical, social, and economic consequences. It is well recognized that a combination of low bone mass and the deterioration of the trabecular architecture underlies osteoporotic fractures. A comprehensive understanding of the relationships between bone mass, the three-dimensional (3D) architecture of bone and bone function is fundamental to the study of new and existing therapies for osteoporosis. Detailed analysis of 3D trabecular architecture, using high-resolution digital imaging techniques such as magnetic resonance microimaging (MRmicroI), micro-computed tomography (microCT), and direct image analysis, has become feasible only recently. Rapid prototyping technology is used to replicate the complex trabecular architecture on a macroscopic scale for visual or biomechanical analysis. Further, a complete set of 3D image data provides a basis for finite element modeling (FEM) to predict mechanical properties. The goal of this paper is to describe how we can integrate three-dimensional microimaging and image analysis techniques for quantitation of trabecular bone architecture, FEM for virtual biomechanics, and rapid prototyping for enhanced visualization. The integration of these techniques provide us with an unique ability to investigate the role of bone architecture in osteoporotic fractures and to support the development of new therapies.

Mitochondrial K(ATP) channel opening is important during index ischemia and following myocardial reperfusion in ischemic preconditioned rat hearts

We have previously demonstrated that K(ATP)channel openers administered just prior to and throughout reperfusion induce cardioprotection in the blood-perfused canine heart. However, a recent report suggests that the mitochondrial K(ATP)channel is only a trigger of ischemic preconditioning (IPC). These recent data are, however, in contrast to most previous investigations that suggested that activation of the mitochondrial K(ATP)channel is an important downstream mediator of cardioprotection. Therefore, we examined the role of the mitochondrial K(ATP)channel as a downstream mediator of IPC in a rat model by administering the selective mitochondrial K(ATP)channel antagonist, 5-hydroxydecanoate (5-HD), at several points during IPC. Infarct size (IS) was determined by tetrazolium chloride staining and expressed as a percent of the area at risk (AAR). Control animals had an IS/AAR of 58.4+/-0.6 and IS/AAR was reduced to 6.2+/-1.7 following IPC. 5-HD (10 mg/kg), attenuated cardioprotection when administered either 5 min prior to the IPC stimulus (40.4+/-1.4), during the reperfusion phase of the IPC stimulus (39.7+/-5.9), or 5 min prior to reperfusion during prolonged ischemia (34.3+/-6.9). Additionally, when 5-HD was administered at 5 mg/kg during the reperfusion phase of index ischemia plus 5 min prior to IPC or plus during the reperfusion phase of IPC, cardioprotection was also attenuated (36.3+/-5.5 and 43.8+/-6.9, respectively). These data suggest that activation of the mitochondrial K(ATP) channel is an important downstream regulator of myocardial protection with effects lasting into the reperfusion period following prolonged ischemia.

ERK and p38 MAP kinase activation are components of opioid-induced delayed cardioprotection

Opioids have been previously shown to confer acute and delayed cardioprotection against a prolonged ischemic insult. We have extensively characterized the signal transduction pathway mediating acute cardioprotection and have suggested a role for extracellular signal regulated kinase (ERK) in this cardioprotection. Therefore, we attempted to determine a role for ERK and the stress activated MAP kinase, p38, in opioid-induced delayed cardioprotection by using selective inhibitors of these pathways. All rats were subjected to 30 min of ischemia and 2 h of reperfusion (I/R). Control animals, injected with saline 48 h prior to I/R, had an infarct size/area at risk (IS/AAR) of 61.6 +/- 1.6.48-h pretreatment with TAN-67 (30 mg/kg), a delta1-opioid receptor agonist, maximally reduced IS/AAR (31.2 +/- 6.5). The involvement of ERK was examined with PD 098059, a selective pharmacological antagonist which inhibits the upstream kinase, MEK-1, that phosphorylates and activates ERK. PD 098059 (0.3 mg/kg) did not alter IS/AAR when administered alone (60.7 +/- 4.9). However, PD 098059 (0.3 mg/kg) administration 30 min prior to TAN-67 (30 mg/kg) completely abolished cardioprotection (61.0 +/- 7.6). The selective p38 inhibitor, SB 203580 (1.0 mg/kg), had no effect on IS/AAR in the absence of TAN-67 (53.1 +/- 2.3). Additionally, SB 203580 (1.0 mg/kg) when administered prior to TAN-67 (30 mg/kg) partially abolished cardioprotection (51.3 +/- 6.4). These results suggest that both ERK and p38 are integral components of opioid-induced delayed cardioprotection and may act via parallel pathways.

Cardioprotection is strain dependent in rat in response to whole body hyperthermia

Previous results showed a genetic component to cardioprotection. Therefore, we investigated the heat shock response in Wistar and Sprague-Dawley (SD) rats at 24 and 48 h. Rats were subjected to whole body hyperthermia achieving colonic temperatures of 40 or 42 degrees C for 20 min. After recovery hearts were excised for protein measurements or were subjected to 30 min of ischemia and then 2 h of reperfusion. Heat shock protein (HSP) expression was determined by Western blotting and infarct size was determined by triphenyltetrazolium staining. All groups of SD and Wistar rats demonstrated HSP72 and HSP90 induction at both time points in response to a heat stress of 42 degrees C. At 24 h there was only a significant reduction in infarct size seen in control vs. small SD (60.0 +/- 4.8 vs. 26.5 +/- 2.3) rats. However, at 48 h control versus small SD (60.0 +/- 4.8 vs. 17.6 +/- 3.8) and Wistar (59.4 +/- 4.3 vs. 29.8 +/- 6.0) and control versus large SD (53.7 +/- 2.6 vs. 19.8 +/- 4.7) and Wistar (57.3 +/- 1.6 vs. 34.5 +/- 2.8) rats demonstrated a significant reduction in infarct size with a greater reduction observed in SD rats. We conclude that heat shock-induced cardioprotection in rats is dependent on strain, temperature, time after stress, and size.

Essential activation of PKC-delta in opioid-initiated cardioprotection

Stimulation of the delta(1)-opioid receptor confers cardioprotection to the ischemic myocardium. We examined the role of protein kinase C (PKC) after delta-opioid receptor stimulation with TAN-67 or D-Ala(2)-D-Leu(5)-enkephalin (DADLE) in a rat model of myocardial infarction induced by a 30-min coronary artery occlusion and 2-h reperfusion. Infarct size (IS) was determined by tetrazolium staining and expressed as a percentage of the area at risk (IS/AAR). Control animals, subjected to ischemia and reperfusion, had an IS/AAR of 59.9 +/- 1.8. DADLE and TAN-67 administered before ischemia significantly reduced IS/AAR (36.9 +/- 3.9 and 36.7 +/- 4.7, respectively). The delta(1)-selective opioid antagonist 7-benzylidenenaltrexone (BNTX) abolished TAN-67-induced cardioprotection (54.4 +/- 1.3). Treatment with the PKC antagonist chelerythrine completely abolished DADLE- (61.8 +/- 3.2) and TAN-67-induced cardioprotection (55.4 +/- 4.0). Similarly, the PKC antagonist GF 109203X completely abolished TAN-67-induced cardioprotection (54.6 +/- 6.6). Immunofluorescent staining with antibodies directed against specific PKC isoforms was performed in myocardial biopsies obtained after 15 min of treatment with saline, chelerythrine, BNTX, or TAN-67 and chelerythrine or BNTX in the presence of TAN-67. TAN-67 induced the translocation of PKC-alpha to the sarcolemma, PKC-beta(1) to the nucleus, PKC-delta to the mitochondria, and PKC-epsilon to the intercalated disk and mitochondria. PKC translocation was abolished by chelerythrine and BNTX in TAN-67-treated rats. To more closely examine the role of these isoforms in cardioprotection, we utilized the PKC-delta selective antagonist rottlerin. Rottlerin abolished opioid-induced cardioprotection (48.9 +/- 4.8) and PKC-delta translocation without affecting the translocation of PKC-alpha, -beta(1), or -epsilon. These results suggest that PKC-delta is a key second messenger in the cardioprotective effects of delta(1)-opioid receptor stimulation in rats.

Opioids and cardioprotection

Opioid peptides and exogenous opioids such as morphine are known to exert important cardiovascular effects. However, until recently, it was not appreciated that activation of specific receptors results in a potent cardioprotective effect to reduce infarct size in experimental animals and to reduce cell death in isolated cardiomyocytes. In intact rat and rabbit hearts, nonselective opioid receptor antagonists such as naloxone and a selective delta1-opioid receptor antagonist, 7-benzylidenenaltrexone, have been shown to inhibit the cardioprotective effect of ischemic preconditioning, a phenomenon in which brief periods of ischemia protect the heart against a more prolonged period of ischemia. Selective delta(1) specific agonists such as 2-methyl-4a-alpha-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12a-alpha-octahydroquinolino[2,3,3-g]isoquinoline have been shown to exert potent cardioprotective effects in intact animals and cardiac myocytes via activation of Gi/o proteins, protein kinase C, and ultimately, the mitochondrial KATP channel. These protective effects occur immediately following drug administration, and reappear 24-48 hr post treatment. Although further studies are needed to more clearly define the mechanisms by which opioids exert their cardioprotective effects, the data accumulated and summarized in this review suggest that this class of drugs may not only be useful in alleviating the pain associated with a myocardial infarction, but may also be simultaneously reducing the size of the ultimate infarct. Since many of these drugs are already clinically available, a long period of drug development may not be necessary before the use of these drugs reaches the patient with signs of myocardial ischemia.