Gadolinium attenuates regional stunning in the canine heart in vivo

Gadolinium limits myocardial infarction in the rat: dose-response, temporal relations and mechanisms

The lanthanide cation, gadolinium (Gd) attenuates post-ischemic myocardial stunning. This study tests the hypothesis that Gd also preconditions the myocardium against infarction following ischemia-reperfusion (IR) and explores potential mechanisms underlying Gd-induced cardioprotection. Regional myocardial infarction was induced in rats by occluding the left anterior descending artery for 30 min and reperfusing for 120 min. Rats (n=6/group) were administered intravenous Gd (1 to 100 micromol/kg) 15 min prior to ischemia. Hearts were excised after reperfusion to determine infarct size (IS) and area at risk (AAR). The ratio IS/AAR (%) was reduced by Gd in a "U"-shaped, dose-dependent manner. The minimum dose that reduced IS/AAR was 5 micromol/kg (52+/-5% vs. 64+/-4%), while the dose that reduced IS/AAR maximally was 20 micromol/kg (44+/-4%). Gd also reduced IS/AAR when given 1 min before reperfusion (47+/-3%) but not when given 10 s after reperfusion (60+/-3%). Cardioprotection was maintained if IR was delayed 24-72 h after Gd administration. Cardioprotection by Gd was abolished by inhibition of JAK-2 with AG-490, of p42/44 MAPK with PD98059 or of K(ATP) channels with glibenclamide. None of these agents given alone altered IS/AAR compared with controls. Inhibition of JAK-2 also blocked Gd-induced delayed cardioprotection. Gd may have broad potential roles in IR, as it conferred immediate cardioprotection when given prior to ischemia or prior to reperfusion and delayed cardioprotection for up to 72 h after administration. The mechanism underlying Gd-induced preconditioning appears to be multi-factorial, involving JAK-2, STAT-3 and p44 MAPK pathways, as well as K(ATP) channels.

Cardioprotective effects of stretch are mediated by activation of sarcolemmal, not mitochondrial, ATP-sensitive potassium channels

To determine whether sarcolemmal and/or mitochondrial ATP-sensitive potassium (K(ATP)) channels (sarcK(ATP), mitoK(ATP)) are involved in stretch-induced protection, isolated isovolumic rat hearts were assigned to the following protocols: nonstretched hearts were subjected to 20 min of global ischemia (Is) and 30 min of reperfusion, and before Is stretched hearts received 5 min of stretch + 10 min of no intervention. Stretch was induced by a transient increase in left ventricular end-diastolic pressure (LVEDP) from 10 to 40 mmHg. Other hearts received 5-hydroxydecanoate (5-HD; 100 microM), a selective inhibitor of mitoK(ATP), or HMR-1098 (20 microM), a selective inhibitor of sarcK(ATP), before the stretch protocol. Systolic function was assessed through left ventricular developed pressure (LVDP) and maximal rise in velocity of left ventricular pressure (+dP/dt(max)) and diastolic function through maximal decrease in velocity of left ventricular pressure (-dP/dt(max)) and LVEDP. Lactate dehydrogenase (LDH) release and ATP content were also measured. Stretch resulted in a significant increase of postischemic recovery and attenuation of diastolic stiffness. At 30 min of reperfusion LVDP and +dP/dt(max) were 87 +/- 4% and 92 +/- 6% and -dP/dt(max) and LVEDP were 95 +/- 9% and 10 +/- 4 mmHg vs. 57 +/- 6%, 53 +/- 6%, 57 +/- 10%, and 28 +/- 5 mmHg, respectively, in nonstretched hearts. Stretch increased ATP content and did not produce LDH release. 5-HD did not modify and HMR-1098 prevented the protection achieved by stretch. Our results show that the beneficial effects of stretch on postischemic myocardial dysfunction, cellular damage, and energetic state involve the participation of sarcK(ATP) but not mitoK(ATP).

Effects of gadolinium on regionally stunned myocardium: temporal considerations

OBJECTIVES

The lanthanide cation, gadolinium (Gd(3+)), accelerates recovery of stunned myocardium when given prior to ischemia. This study sought to determine whether giving Gd(3+) during ischemia or during reperfusion also ameliorates stunning, as these temporal relationships could help determine the clinical utility of this novel agent.

METHODS

Regional myocardial stunning was induced in anesthetized dogs by coronary occlusion for 15 min followed by reperfusion for 3 h. Gd(3+) (500 micromol) was given intravenously in three treatment groups: [1] preischemia; [2] during ischemia; [3] after reperfusion. No Gd(3+) was given to controls (Group 4). Measures of global and regional myocardial function were assessed serially.

RESULTS

Treatment with Gd(3+) prior to ischemia (Group 1) had no effects on hemodynamics or regional contraction. Coronary occlusion resulted in diastolic lengthening and paradoxical systolic bulging equally in all groups. After 3 h of reperfusion, regional systolic shortening (%) in the stunned segment was greater in Groups 1 (10.9 +/- 3.4; P = 0.02) and 2 (6.6 +/- 1.3; P = 0.047) compared with controls (-0.6 +/- 0.03). Recovery of systolic function (% of baseline shortening) after 3 h of reperfusion was similarly improved in Groups 1 (56.1 +/- 16.8; P = 0.02) and 2 (43.3 +/- 8.1; P = 0.04) compared with controls (-11.5 +/- 4.7).

CONCLUSIONS

Gadolinium has no inherent inotropic effects but enhances recovery of stunned myocardium. This effect appears maximal if Gd(3+) is given prior to ischemia, indicating potential utility in elective cardiac surgical procedures or percutaneous coronary interventions. Gadolinium also enhances recovery if given during ischemia but prior to reperfusion, and may thus be useful in acute coronary syndromes as well.

Gadolinium does not blunt the cardiovascular responses at the onset of voluntary static exercise in cats: a predominant role of central command

The cardiovascular adaptation at the onset of voluntary static exercise is controlled by the autonomic nervous system. Two neural mechanisms are responsible for the cardiovascular adaptation: one is central command descending from higher brain centers, and the other is a muscle mechanosensitive reflex from activation of mechanoreceptors in the contracting muscles. To examine which mechanism played a major role in producing the initial cardiovascular adaptation during static exercise, we studied the effect of intravenous administration of gadolinium (55 micromol/kg), a blocker of stretch-activated ion channels, on the increases in heart rate (HR) and mean arterial blood pressure (MAP) at the onset of voluntary static exercise (pressing a bar with a forelimb) in conscious cats. HR increased by 31 +/- 5 beats/min and MAP increased by 15 +/- 1 mmHg at the onset of voluntary static exercise. Gadolinium affected neither the baseline values nor the initial increases of HR and MAP at the onset of exercise, although the peak force applied to the bar tended to decrease to 65% of the control value before gadolinium. Furthermore, we examined the effect of gadolinium on the reflex responses in HR and MAP (18 +/- 7 beats/min and 30 +/- 6 mmHg, respectively) during passive mechanical stretch of a forelimb or hindlimb in anesthetized cats. Gadolinium significantly blunted the passive stretch-induced increases in HR and MAP, suggesting that gadolinium blocks the stretch-activated ion channels and thereby attenuates the reflex cardiovascular responses to passive mechanical stretch of a limb. We conclude that the initial cardiovascular adaptation at the onset of voluntary static exercise is predominantly induced by feedforward control of central command descending from higher brain centers but not by a muscle mechanoreflex.

Antagonists of stretch-activated ion channels restore contractile function in hamster dilated cardiomyopathy

BACKGROUND

Stretch-activated ion channels (SACs) mediate abnormal ion currents in dilated cardiomyopathy (DCM), but their role in the contractile defect of DCM is undefined. We hypothesized that SAC antagonists would enhance contractile function in a hamster model of DCM.

METHODS

Left ventricular papillary muscles from Syrian hamsters with a genetic DCM (n = 26), and from non-myopathic controls (n = 26), were superfused and stimulated to contract. Maximum active force (F(max); milli-Newtons per square millimeter) was determined before (baseline) and after subjecting the muscle to a 60-minute period of overstretch (resting length associated with a 20% decay in baseline maximum force [F(max)]). Gadolinium (10 micromol/liter) and streptomycin (40 micromol/liter) were used separately to antagonize SACs.

RESULTS

In the absence of SAC antagonist, baseline F(max) was greater in controls (1.79 +/- 0.26) vs DCM (0.69 +/- 0.12; p < 0.05). Overstretch caused further decrease in F(max) in DCM (to 0.50 +/- 0.08; p = 0.03 vs baseline), but not in controls. The SAC antagonists increased baseline F(max) in DCM to equal that of untreated controls (gadolinium 1.64 +/- 0.34, streptomycin 2.13 +/- 0.33), but neither agent increased baseline F(max) in controls (gadolinium 1.91 +/- 0.20, streptomycin 2.25 +/- 0.49). Both agents abolished the stretch-induced decrease in contractile function in DCM.

CONCLUSIONS

Antagonists of SACs enhance contractile function in DCM to equal that of normal controls, and abolish sensitivity to further stretch. They do not alter contractile function in normal muscle. These data suggest an important role of SACs in the contractile dysfunction of DCM and further suggest that SAC antagonists may represent novel therapy in heart failure.