Gadolinium prevents stretch-mediated contractile dysfunction in isolated papillary muscles

Application of Cardiovascular Physiology to the Critically Ill Patient

OBJECTIVES

To use the ventricular pressure-volume relationship and time-varying elastance model to provide a foundation for understanding cardiovascular physiology and pathophysiology, interpreting advanced hemodynamic monitoring, and for illustrating the physiologic basis and hemodynamic effects of therapeutic interventions. We will build on this foundation by using a cardiovascular simulator to illustrate the application of these principles in the care of patients with severe sepsis, cardiogenic shock, and acute mechanical circulatory support.

DATA SOURCES

Publications relevant to the discussion of the time-varying elastance model, cardiogenic shock, and sepsis were retrieved from MEDLINE. Supporting evidence was also retrieved from MEDLINE when indicated.

STUDY SELECTION, DATA EXTRACTION, AND SYNTHESIS

Data from relevant publications were reviewed and applied as indicated.

CONCLUSIONS

The ventricular pressure-volume relationship and time-varying elastance model provide a foundation for understanding cardiovascular physiology and pathophysiology. We have built on this foundation by using a cardiovascular simulator to illustrate the application of these important principles and have demonstrated how complex pathophysiologic abnormalities alter clinical parameters used by the clinician at the bedside.

Coronary vasodilator activity of vulgarenol, a sesquiterpene isolated from Magnolia grandiflora, and its possible mechanism

The aim of this study was to investigate the biodynamic effects of vulgarenol, a sesquiterpene isolated from Magnolia grandiflora flower petals and its possible mechanism on the Langendorff isolated and perfused heart model. Vulgarenol (5 microm) caused a statistically significant decrease in coronary vascular resistance (15.21 +/- 6.00 dyn s cm(-5) vs 36.80 +/- 5.01 dyn s cm(-5), control group), increased nitric oxide release (223.01 +/- 8.76 pmol/mL vs 61.00 +/- 12.00 pmol/mL, control group) and cyclic guanosine monophosphate accumulation in left ventricular tissue samples (142.17 +/- 8.41 pmol/mg of tissue vs 43.94 +/- 5.00 pmol/mg of tissue, control group). Pre-treatment with 3 microm gadolinium chloride hexahydrate, 100 microm N(omega)-nitro-L-arginine methyl ester hydrochloride, and 10 microm 1H-[1,2,4]oxadiazolo[4,2-a]quinoxalin-1-one significantly abolished the vulgarenol-induced coronary vascular resistance decrease, nitric oxide increased release and cGMP accumulation in left ventricular tissue samples. The results support the fact that nitric oxide and cyclic guanosine monophosphate are likely involved in the endothelium-dependent coronary vasodilation.

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.

Viscum albumaqueous extract induces NOS-2 and NOS-3 overexpression in Guinea pig hearts

Viscum album L. aqueous extract, on the Langendorff isolated and perfused heart model, decreases coronary vascular resistance, when compared to control group (36.00 +/- 2.00 vs. 15.80 +/- 1.96 dyn s cm-5). Our data support the fact that this mechanism involves NOS-2 and NOS-3 overexpression (4.65 and 7.89 times over control, respectively), which is correlated with increases in NO (6.24 +/- 2.49 vs. 147.95 +/- 2.79 pmol) and cGMP production (43.94 +/- 2.00 vs. 74.81 +/- 1.96 pmol mg-1 of tissue), compared to control values. Such an effect is antagonized by gadolinium(III) chloride, L-NAME and ODQ. Therefore, coronary vasodilator effect elicited by V. album L. aqueous extract is mediated by the NO/sGC pathway.

Mechanisms Underlying Afterload-Induced Exacerbation of Myocardial Infarct Size

One consequence of elevated afterload pressure is the activation of the angiotensin II type 1 receptor and nonspecific cation channels with subsequent Ca 2+ accumulation via the Na + /H + -Na + /Ca 2+ exchanger combination and the T-type or L-type Ca 2+ channels. Intracellular Ca 2+ overload is cytotoxic, in part, by inducing the mitochondrial permeability transition (MPT) pore. Therefore, we tested the hypotheses that: (1) increased afterload pressure worsens myocardial ischemia-reperfusion injury in healthy heart, (2) the Na + /H + -Na + /Ca 2+ exchanger combination and both the T-type and L-type Ca 2+ channels are involved in the exacerbating impact of high afterload pressure on infarct size, and (3) elevated afterload enhances infarct size in part via the MPT pore. Accordingly, the effect of candesartan (angiotensin II type 1 receptor antagonist), cariporide (inhibitor of the Na + /H + exchanger), mibefradil (T-type Ca 2+ channel blocker), diltiazem (L-type Ca 2+ channel blocker), or cyclosporine A (inhibitor of MPT pore) were examined. The elevation in afterload pressure from 80 to 160 cmH 2 O increased baseline myocardial performance but caused larger infarcts and worsened recovery of mechanical function after ischemia reperfusion. Whereas mibefradil abrogated the effect of high afterload pressure on infarct size, the other agents reduced infarct size at both afterload pressures. Hearts exposed to mibefradil, diltiazem, or cariporide displayed greater functional recovery than those exposed to candesartan or cyclosporine A, revealing that an uncoupling exists between reduced cell death and recovery of mechanical function of the viable portions of the myocardium. The data also uncovered an important link between pressure-mediated exacerbation of infarct size and T-type Ca 2+ channel activity.

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.

Functional relevance of the stretch-dependent slow force response in failing human myocardium

Stretch induces immediate and delayed inotropic effects in mammalian myocardium via distinct mechanosensitive pathways, but these effects are poorly characterized in human cardiac muscle. We tested the effects of stretch on immediate and delayed force response in failing human myocardium. Experiments were performed in muscle strips from 52 failing human hearts (37 degrees C, 1 Hz, bicarbonate buffer). Muscles were stretched from 88% of optimal length to 98% of optimal length. The resulting immediate and delayed (ie, slow force response [SFR]) increases in twitch force were assessed without and after blockade of the sarcoplasmic reticulum (SR; cyclopiazonic acid and ryanodine), stretch-activated ion channels (SACs; gadolinium, streptomycin), L-type Ca2+-channels (diltiazem), angiotensin II type-1 (AT1) receptors (candesartan), endothelin (ET) receptors (PD145065 or BQ123), Na+/H+ exchange (NHE1; HOE642), or reverse-mode Na+/Ca+ exchange (NCX; KB-R7493). We also tested the effects of stretch on SR Ca2+ load (rapid cooling contractures [RCCs]) and intracellular pH (in BCECF-loaded trabeculae). Stretch induced an immediate (<10 beats), followed by a slow (5 to 10 minutes), force response. Twitch force increased to 232+/-6% of prestretch value during the immediate phase, followed by a further increase to 279+/-8% during the SFR. RCC amplitude significantly increased, but pHi did not change during SFR. Inhibition of SACs, L-type Ca2+ channels, AT1 receptors, or ET receptors did not affect the stretch-dependent immediate or SFR. In contrast, the SFR was reduced by NHE1 inhibition and almost completely abolished by reverse-mode NCX inhibition or blockade of sarcoplasmic reticulum function. The data demonstrate the existence of a functionally relevant, SR-Ca2+-dependent SFR in failing human myocardium, which partly depends on NHE1 and reverse-mode NCX activation.

Intracellular sodium in mammalian muscle fibers after eccentric contractions

The effect of eccentric contractions on intracellular Na(+) concentration ([Na(+)](i)) and its distribution were examined in isolated rat and mouse muscle fiber bundles. [Na(+)](i) was measured with either Na(+)-binding benzofuran isophthalate or sodium green. Ten isometric contractions had no significant effect on force (measured after 5 min of recovery) and caused no significant change in the resting [Na(+)](i) (7.2 +/- 0.5 mM). In contrast 10 eccentric contractions (40% stretch at 4 muscle lengths/s) reduced developed force at 100 Hz to 45 +/- 3% of control and increased [Na(+)](i) to 16.3 +/- 1.6 mM (n = 6; P < 0.001). The rise of [Na(+)](i) occurred over 1-2 min and showed only minimal recovery after 30 min. Confocal images of the distribution of [Na(+)](i) showed a spatially uniform distribution both at rest and after eccentric contractions. Gd(3+) (20 microM) had no effect on resting [Na(+)](i) or control tetanic force but prevented the rise of [Na(+)](i) and reduced the force deficit after eccentric damage. These data suggest that Na(+) entry after eccentric contractions may occur principally through stretch-sensitive channels.

Gadolinium attenuates regional stunning in the canine heart in vivo

OBJECTIVE

Gadolinium, a lanthanide cation, ameliorates pathophysiologic features of both heart failure and cardiac arrhythmias. We have shown, in an in vitro model, that gadolinium blocks stretch-induced contractile dysfunction in both normal and stunned myocardium. The present study tested the hypothesis that gadolinium would also attenuate regional myocardial stunning in an in vivo model.

METHODS

Mongrel dogs (n = 13) were subjected to regional myocardial ischemia (occlusion of the left anterior descending coronary artery) for 15 minutes, followed by reperfusion for 180 minutes. Intravenous gadolinium (500 micromol) was given to 7 dogs before ischemia; no gadolinium was given to control animals. Regional contractile function was assessed serially by means of both systolic shortening (percentage) and regional preload recruitable stroke work.

RESULTS

Administration of gadolinium before ischemia had no effect on heart rate, arterial blood pressure, stroke volume, or regional contractile function. Ischemia resulted in paradoxical systolic bulging in both groups. After 180 minutes of reperfusion, systolic shortening was enhanced in gadolinium-treated animals compared with that in control animals (10.9% +/- 1.5% vs 2.4% +/- 1.7%, P =.003). Both the slope and x-axis intercept of regional preload recruitable stroke work returned to preischemic values in treated animals but remained abnormal in control animals.

CONCLUSIONS

These data confirm that gadolinium attenuates regional myocardial stunning in vivo. Gadolinium may cause peripheral vasodilatation but does not appear to exert positive inotropic effects on the normal canine heart. The mechanism underlying gadolinium-mediated effects on stunned myocardium remains undefined, but this study suggests that use of gadolinium may represent a novel adjunct to current cardioprotective strategies.

Increased coronary perfusion augments cardiac contractility in the rat through stretch-activated ion channels

The role of stretch-activated ion channels (SACs) in coronary perfusion-induced increase in cardiac contractility was investigated in isolated isometrically contracting perfused papillary muscles from Wistar rats. A brief increase in perfusion pressure (3-4 s, perfusion pulse, n = 7), 10 repetitive perfusion pulses (n = 4), or a sustained increase in perfusion pressure (150-200 s, perfusion step, n = 7) increase developed force by 2.7 +/- 1.1, 7.7 +/- 2.2, and 8.3 +/- 2.5 mN/mm(2) (means +/- SE, P < 0.05), respectively. The increase in developed force after a perfusion pulse is transient, whereas developed force during a perfusion step remains increased by 5.1 +/- 2.5 mN/mm(2) (P < 0.05) in the steady state. Inhibition of SACs by addition of gadolinium (10 micromol/l) or streptomycin (40 and 100 micromol/l) blunts the perfusion-induced increase in developed force. Incubation with 100 micromol/l N(omega)-nitro-L-arginine [nitric oxide (NO) synthase inhibition], 10 micromol/l sodium nitroprusside (NO donation) and 0.1 micromol/l verapamil (L-type Ca(2+) channel blockade) are without effect on the perfusion-induced increase of developed force. We conclude that brief, repetitive, or sustained increases in coronary perfusion augment cardiac contractility through activation of stretch-activated ion channels, whereas endothelial NO release and L-type Ca(2+) channels are not involved.