Atrial natriuretic factor in the Langendorff perfused coronary vasculature of the rabbit isolated heart

Removal of exogenously administered rat ANF (99-126) (rANF) from the rabbit coronary vasculature was investigated. Rabbit hearts were perfused using a modified Langendorff technique and ANF concentrations in the perfusate were measured by a radio-receptor assay. Under these conditions no major degradation of ANF was observed. On perfusion, however, the heart liberated large amounts of ANF. This release peaked 15 minutes after the initiation of perfusion, (685 + 220 pM) and then fell to a sustained basal level (305 + 80 pM) after 45 minutes. Although an increase in the perfusate flow rate reduced the ANF concentration, there was no significant difference in the rate of ANF release between the two flow rates used. After momentary cessation of flow ANF concentration fell to a significantly lower level, however, once again no significant change in rate of release occurred. These results suggest that the heart is not a major site of ANF degradation and that alterations in flow rate through the coronary vascular bed can cause changes in amounts of ANF released.     

Mechanical compression elicits NO-dependent increases in coronary flow

Our previous studies have demonstrated that a decrease in arteriolar diameter that causes endothelial deformation elicits the release of nitric oxide (NO). Thus we hypothesized that cardiac contraction, via deformation of coronary vessels, elicits the release of NO and increases in coronary flow. Coronary flow was measured at a constant perfusion pressure of 80 mmHg in Langendorff preparations of rat hearts. Hearts were placed in a sealed chamber surrounded with perfusion solution. The chamber pressure could be increased from 0 to 80 mmHg to generate extracardiac compression. To minimize the impact of metabolic vasodilatation and rhythmic changes in shear stress, nonbeating hearts, by perfusing the hearts with a solution containing 20 mM KCl, were used. After extracardiac compression for 10 or 20 s, coronary flow increased significantly, concurrent with an increased release of nitrite into the coronary effluent and increased phosphorylation of endothelial NO synthase in the hearts. Inhibition of NO synthesis eliminated the compression-induced increases in coronary flow. Shear stress-induced dilation could not account for this increased coronary flow. Furthermore, in isolated coronary arterioles, without intraluminal flow, the release of vascular compression elicited a NO-dependent dilation. Thus this study reveals a new mechanism that, via coronary vascular deformation, elicited by cardiac contraction, stimulates the endothelium to release NO, leading to increased coronary perfusion.     

Hypoxia-induced release of atrial natriuretic factor (ANF) from the isolated rat and rabbit heart

The effect of hypoxia on the release of atrial natriuretic factor (ANF) was studied in isolated, constant-flow perfused hearts of rats and rabbits. Effluent samples were frozen pending extraction and radioimmunoassay of ANF. Hypoxia (10 min) caused a 3.9-fold (rats) and 4.6-fold (rabbits) increase of ANF release over control values. ANF release returned to control levels within 8-11 min of reoxygenation. Prolonged (20 min) hypoxia evoked further ANF release. The increase in ANF release and decrease in ventricular pressure, heart rate and coronary perfusion pressure were fully reversible, suggesting that tissues were not damaged. These results demonstrate that hypoxia induces a massive release of ANF by an as yet unexplained mechanism.     

Preliminary observations on the effects of stimulation of cardiac nerves in man

The dorsal mediastinal cardiac nerves were stimulated in 20 patients undergoing coronary artery bypass surgery. In no instance was an untoward effect produced in any of the patients. Stimulation of a cardiac nerve increased heart rate in eight patients and slowed heart rate in eight patients. In 12 patients stimulation of a cardiac nerve increased mean aortic pressure while in 8 patients it was decreased, even though the patients were supported by a total body perfusion pump. In 11 patients stimulation of a cardiac nerve resulted in a decrease in the coronary artery bypass graft flow, even though aortic pressure was unchanged or increased. These preliminary results suggest that individual cardiac nerves in the dorsal mediastinum of man may be capable of modifying heart rate, total peripheral vascular resistance, or coronary artery resistance. Furthermore, they demonstrate that stimulation of human dorsal mediastinal cardiac nerves can be done without untoward effects and that such stimulations may be a means to investigate the complexity of neural regulation of the human heart.     

Hemodynamic and plasma atrial natriuretic factor responses to cardiac volume loading in young versus older normotensive humans.

To assess the effects of age on responsiveness of atrial natriuretic factor (ANF) release, and the possible contribution of cardiac sympathetic activity, in young (n = 8) and older normotensives (n = 7), the effects of cardiac volume load on plasma ANF, central venous pressure, and general hemodynamics were evaluated. Studies were performed after pretreatment with placebo or 80 mg propranolol. Cardiac volume loading increased central venous pressure by 3-5 mmHg (1 mmHg = 133.3 Pa); beta-blockade did not affect this response. Cardiac volume load caused significant increases in heart rate (10-15 beats/min) and cardiac index (by 0.7-0.8 L.min-1.m-2) and decreases in plasma catecholamines. Propranolol attenuated the increases in heart rate and cardiac index. These hemodynamic responses did not differ significantly between the two groups of subjects. Cardiac volume load significantly increased plasma ANF, by 87 +/- 21 pg/mL in the young normotensives and by 212 +/- 33 pg/mL in the older normotensives (p < 0.01, young vs. older). beta-Blockade did not affect this different response. Our results show that the plasma ANF response to volume loading is potentiated by aging. Although differences in atrial stretch cannot be excluded, this effect may relate to the decrease in clearance of plasma ANF occurring with aging.     

Effects of ischemia on the metabolism of cardiac enkephalins

The effect of ischemia on cardiac Leucine enkephalin (Leu-enk) content, degradation and coronary release was studied in the isolated perfused hearts of male Sprague Dawley rats. Hearts were electrically stimulated at 180 beats/min. Cardiac Leu-enk concentrations were increased when hearts were perfused (635 +/- 41 vs 301 +/- 60 fmol/g in control non-perfused hearts,) or during ischemia-reperfusion (520 +/- 78 vs 277 +/- 42 fmol/g in heart submitted to ischemia alone). The quantity of leucine-enkephalin released by the heart during perfusion was four times higher than the initial content measured in the heart tissue. The rate of this release was the same throughout the experiment (25.9 +/- 2.9 fmol/min/g during perfusion vs. 19.2 +/- 1.6 during ischemia-reperfusion). These findings suggested that cardiac enkephalin metabolism is regulated by cardiac events. In fact, enzymes involved in enkephalin degradation were decreased during perfusion (39%) and increased during ischemia (50%). The decrease in the enzyme activity during coronary perfusion depended on a reduced activity in the membrane fraction only while membrane and soluble fractions were interested in the increased enzyme activity after ischemia. Ischemia-reperfusion induced a larger release of Leu-enk than perfusion without ischemia. In view of the protective actions of enkephalin peptides against oxidative stress, we can infer from our results an implication of Leu-enk in ischemia-reperfusion and thus eventually in preconditioning phenomenon.     

Cardiac anaphylaxis in isolated guinea pig hearts perfused at constant flow or constant pressure

Acute responses to antigen-antibody interactions (anaphylactic reactions) in isolated guinea pig hearts are reported to include decreases in coronary flow, increases in heart rate, prolongation of impulse propagation, development of arrhythmias, and transient increases followed by substantial decreases in ventricular contractile force. It is not clear from these studies, however, whether all of the changes are direct effects of the mediators released by the antigen-antibody reaction or whether some of them are indirect results of the severe reduction in flow evoked by coronary vasoconstriction. Therefore, the present study was designed to assess cardiac anaphylactic events in isolated hearts of guinea pigs passively sensitized with IgG antibody to ovalbumin under conditions in which coronary perfusion pressure was maintained constant and to compare the responses to those of hearts in which coronary flow was maintained at a constant rate. Our data indicate that when coronary flow decreased during anaphylaxis (constant pressure perfusion), hearts responded to antigen challenge with greater prolongation of the PR interval, duration of arrhythmias, suppression of left ventricular systolic pressure, and release of histamine and adenosine plus inosine into the venous effluent than when coronary flow was maintained during anaphylaxis (constant flow perfusion). The data suggest that maintenance of coronary flow during cardiac anaphylaxis may attenuate the severity of the functional derangement.     

Contrasting views on the action of atrial peptides: lessons from studies of conscious animals

In a rather short time, a consensus seems to have emerged among researchers regarding the mechanisms of the natriuretic and hypotensive actions of atrial natriuretic factor (ANF). According to the by now classic view, the natriuresis induced by ANF is mediated by changes in renal hemodynamics; vasorelaxation is proposed as the primary mechanism of its hypotensive action. Recent evidence, mostly from experiments with conscious animals, does not support this view. Results from experiments performed with chronically instrumented spontaneously hypertensive rats and normotensive (Wistar-Kyoto and Wistar) rats show that the natriuresis induced by a synthetic ANF is not accompanied by increases in glomerular filtration rate or renal blood flow. Measurement of cardiac output (CO) and blood pressure indicate that a decrease in CO, not a fall in total peripheral resistance, is the cause of the decrease in blood pressure. Based on this and other available evidence, a hypothetical scheme for the biological role of ANF is proposed.     

Mechanosensitive release of parathyroid hormone-related peptide from coronary endothelial cells

10.1152/ajpheart.00925. 2001.-Parathyroid hormone-related peptide (PTHrP) is expressed throughout the cardiovascular system and is able to dilate vessels. This study investigated whether mechanical forces generated by changes in regional perfusion influence PTHrP release from the coronary vascular bed. Experiments were performed in vitro on saline-perfused rat hearts or isolated coronary endothelial cells exposed to cyclic strain and in vivo in anesthetized pigs. In vitro, PTHrP release from saline-perfused rat hearts was strongly correlated with coronary flow (r = 0.84). Increasing coronary flow from 5 to 10 ml/min increased PTHrP release from 442 +/- 42 to 1,563 +/- 167 pg/min. Increasing the viscosity of the perfusate did not change basal PTHrP release. Increasing flow without a concomitant increase in pressure did not lead to an increase in release rate, but reduction in pressure under flow-constant conditions reduced PTHrP release rate. Cyclic strain induced a strain-dependent release of PTHrP from endothelial cells that was inhibited by the addition of a calcium-chelating agent. In vivo, there was a net release of PTHrP in the coronary circulation and decreases in coronary flow and pressure decreased the PTHrP release rate. Bradykinin in the presence of constant pressure increased PTHrP release, probably by increasing the intracellular calcium concentration in coronary endothelial cells. In summary, mechanical forces evoked by blood flow can trigger a constant PTHrP release.     

Prostacyclin-mediated compensatory mechanism in the coronary circulation during acute NO synthase blockade

Nitric oxide (NO) in contrast to most prostanoids, plays a major role in the maintenance of coronary arterial tone under physiological conditions. However, in case of endothelial damage or other NO-depleting situations the importance of other vasodilating mechanisms may be increased. The aim of the present study was to investigate the crosstalk between the L-arginine - NO and the prostanoid systems in isolated rat hearts. Coronary flow and cardiac dynamics were measured in a standard Langendorff perfusion system. Application of indomethacin in the perfusion media failed to change coronary flow. Administration of L-NA, however, significantly decreased coronary flow by 24.8 +/- 2.3% (p < 0.01 vs. untreated control). In the presence of indomethacin, L-NA decreased coronary flow to an even greater extent by 35.8 +/- 5.2% (p < 0.05 vs. L-NA alone). Treatment of the preparations with L-NA or indomethacin failed to change cardiac work, coapplication of both drugs together, however, decreased cardiac work by 45 +/- 11% (p < 0.05 vs. untreated control). Heart rate remained constant throughout the experimental period and did not differ significantly between the treatment groups. The prostacyclin content of the effluent from the L-NA treated hearts was significantly higher than that of controls. We conclude that in case of decreased NO levels in the coronary circulation, arterial tone is maintained by prostacyclin production.     

Positive inotropic, positive chronotropic and coronary vasodilatory effects of rat amylin: mechanisms of amylin-induced positive inotropy

Even though there are a few studies dealing with the cardiac effects of amylin, the mechanisms of amylin-induced positive inotropy are not known well. Therefore, we investigated the possible signaling pathways underlying the amylin-induced positive inotropy and compared the cardiac effects of rat amylin (rAmylin) and human amylin (hAmylin).Isolated rat hearts were perfused under constant flow condition and rAmylin or hAmylin was infused to the hearts. Coronary perfusion pressure, heart rate, left ventricular developed pressure and the maximum rate of increase of left ventricular pressure (+dP/dtmax) and the maximum rate of pressure decrease of left ventricle (-dP/dtmin) were measured.rAmylin at concentrations of 1, 10 or 100 nM markedly decreased coronary perfusion pressure, but increased heart rate, left ventricular developed pressure, +dP/dtmax and -dP/dtmin. The infusion of H-89 (50 μM), a protein kinase A (PKA) inhibitor did not change the rAmylin (100 nM)-induced positive inotropic effect. Both diltiazem (1 μM), an L-type Ca2+ channel blocker and ryanodine (10 nM), a sarcoplasmic reticulum (SR) Ca2+ release channel opener completely suppressed the rAmylin-induced positive inotropic effect, but staurosporine (100 nM), a potent protein kinase C (PKC) inhibitor suppressed it partially. hAmylin (1, 10 and 100 nM) had no significant effect on coronary perfusion pressure, heart rate and developed pressure, +dP/dtmax and -dP/dtmin.We concluded that rAmylin might have been produced vasodilatory, positive chronotropic and positive inotropic effects on rat hearts. Ca2+ entry via L-type Ca2+ channels, activation of PKC and Ca2+ release from SR through ryanodine-sensitive Ca2+ channels may be involved in this positive inotropic effect. hAmylin may not produce any significant effect on perfusion pressure, heart rate and contractility in isolated, perfused rat hearts.     

Norepinephrine amplifies effects of vasopressin on the isolated rat heart.

We compared effects of perfusion of norepinephrine (NE, 10(-9) mol l-1 and of unchanged Krebs-Henseleit solution on the cardiac response to bolus injection of arginine vasopressin (AVP, 2 ng). 14 isolated rat working heart preparations were used in a balanced cross-over design. Coronary flow, oxygen consumption and extraction, heart rate and total flow were continuously recorded. The concentration of NE was below that exerting per se systematic influences on cardiac activity. However, NE changed the cardiac response to AVP: (1) the AVP-induced reduction in coronary flow was greater during NE (mean: 41.7%) than vehicle perfusion (30.5%, P less than 0.005. (2) The AVP-induced decrease in oxygen consumption was stronger on top of the NE (41.5%) than vehicle perfusion (33.6%, P less than 0.005). (3) Following AVP, oxygen extraction during NE was increased compared to oxygen extraction during vehicle perfusion (3.61 +/- 0.03 vs. 3.46 +/- 0.02 microliters O2 ml-1 g-1, P less than 0.005). Results support the view of a potentiating role of catecholamines for direct cardiovascular effects of AVP.     

Effects of atrial natriuretic factor on urinary concentration of catecholamines and renin secretion in dogs

This study evaluated the effects of synthetic atrial natriuretic factor (ANF) on renal hemodynamics, urinary excretion of electrolytes, norepinephrine (NE), and dopamine (DA); and renal production of renin in anesthetized dogs. Following a bolus (1 micrograms/kg body weight) and infusion (0.1 microgram/kg/min) for 30 min, there was significant increase in urine flow (220 +/- 41%), glomerular filtration rate (72 +/- 14%), and urinary sodium excretion (170 +/- 34%). There was a decrease in renin secretory rate and the concentration ratio of urine NE to DA following ANF was decreased (p less than 0.05). These data suggest that ANF decreases renal production of NE and renin.     

Effects of atrial natriuretic factor on blood pressure and the renin-angiotensin-aldosterone system

Atrial natriuretic factor (ANF) antagonizes vasoconstriction induced by numerous smooth muscle agonists and also lowers blood pressure in intact animals. ANF has particularly marked relaxant effects on angiotensin II-contracted vessels in vitro. Sensitivity to the blood pressure-lowering effect of ANF in vivo appears to be enhanced in renin-dependent models of renovascular hypertension compared with other experimental hypertensive models. The depressor action of low, possibly physiological doses of ANF in two-kidney, one-clip Goldblatt rats is due to a decrease in total peripheral resistance. On the other hand, high doses of ANF can lower cardiac output, particularly in volume-expanded models such as deoxycorticosterone-salt hypertension. ANF markedly inhibits renin secretion in intact animals, probably via increased glomerular filtration rate and load of sodium chloride to the macula densa. This effect is masked when renal perfusion is impaired (e.g., via unilateral renal artery constriction), in which case ANF may stimulate renin secretion slightly. ANF also reduces plasma aldosterone in vivo and inhibits basal and agonist-induced aldosterone release from isolated adrenal cortical cells. This effect appears to be especially marked for angiotensin-induced aldosterone production in vivo and in vitro. These findings indicate that ANF has potentially important interactions with the renin-angiotensin-aldosterone system and suggest a role for ANF in the homeostatic control of blood pressure as well as of extracellular fluid volume.     

Effects of insulin on the metabolism of the isolated working rat heart perfused with undiluted rat blood

Working rat hearts were perfused with either buffer or with defibrinated, undiluted rat blood dialyzed to remove vasoconstrictor factors. With precautions taken for sterility in the preparation of the perfusate and the apparatus, hearts were obtained which were stable as judged by stroke rate and cardiac output. In these hearts, cardiac output and coronary flow averaged 46.0 and 1.7 ml/g heart per min, respectively. Perfusion with erythrocyte-free buffer depressed cardiac output by 30%, while coronary flow averaged 8.8 ml/g of heart per min. The mean stroke rate of blood-perfused hearts was 300 beats/min but only 240 beats/min during buffer perfusion. In blood-perfused hearts, insulin did not alter stroke rate but significantly lowered coronary flow. The hormone caused a transient increase in cardiac output in hearts perfused with buffer. Insulin did not alter glucose uptake in buffer-perfused hearts but increased lactate release in perfusions with blood. Both serum fatty acids and triacylglycerol fatty acids were significant metabolic fuels in hearts perfused with undiluted blood. The preparation described would appear to be potentially useful for the study of myocardial metabolism in vitro.     

The effects of chronic trimetazidine treatment on mechanical function and fatty acid oxidation in diabetic rat hearts

Clinical and experimental evidence suggest that increased rates of fatty acid oxidation in the myocardium result in impaired contractile function in both normal and diabetic hearts. Glucose utilization is decreased in type 1 diabetes, and fatty acid oxidation dominates for energy production at the expense of an increase in oxygen requirement. The objective of this study was to examine the effect of chronic treatment with trimetazidine (TMZ) on cardiac mechanical function and fatty acid oxidation in streptozocin (STZ)-diabetic rats. Spontaneously beating hearts from male Sprague-Dawley rats were subjected to a 60-minute aerobic perfusion period with a recirculating Krebs-Henseleit solution containing 11 mmol/L glucose, 100 muU/mL insulin, and 0.8 mmol/L palmitate prebound to 3% bovine serum albumin (BSA). Mechanical function of the hearts, as cardiac output x heart rate (in (mL/min).(beats/min).10-2), was deteriorated in diabetic (73 +/- 4) and TMZ-treated diabetic (61 +/- 7) groups compared with control (119 +/- 3) and TMZ-treated controls (131 +/- 6). TMZ treatment increased coronary flow in TMZ-treated control (23 +/- 1 mL/min) hearts compared with untreated controls (18 +/- 1 mL/min). The mRNA expression of 3-ketoacyl-CoA thiolase (3-KAT) was increased in diabetic hearts. The inhibitory effect of TMZ on fatty acid oxidation was not detected at 0.8 mmol/L palmitate in the perfusate. Addition of 1 mumol/L TMZ 30 min into the perfusion did not affect fatty acid oxidation rates, cardiac work, or coronary flow. Our results suggest that higher expression of 3-KAT in diabetic rats might require increased concentrations of TMZ for the inhibitory effect on fatty acid oxidation. A detailed kinetic analysis of 3-KAT using different concentrations of fatty acid will determine the fatty acid inhibitory concentration of TMZ in diabetic state where plasma fatty acid levels are increased.     

A novel sheep model to study the effect of high rate intracoronary perfusion on cardiac electrophysiology

An increase in coronary flow is known to enhance myocardial metabolism and contractility (the Gregg effect) but the effect on cardiac electrophysiology is unclear. In 5 pentobarbital-anesthetised open-chest sheep, left circumflex coronary artery was perfused with fresh arterial blood at 6 and 10 ml/min respectively in the presence of normal coronary flow. The perfusion was repeated in these animals after treatment with nitro-L-arginine, a nitric oxide synthase inhibitor. The high rate intracoronary perfusion caused a flow-dependent T wave inversion on body surface ECG in all animals (p < 0.01). Pre-treatment with nitro-L-arginine abolished T wave inversion during 6 ml/min perfusion, and diminished the T inversion during 10 ml/min perfusion. Conclusion: An increase in coronary flow alters ventricular repolarisation through nitric oxide release from coronary endothelium.     

Mechanism of action of arachidonic acid in the isolated perfused rat heart

The purpose of this study was to elucidate the mechanism of action of arachidonic acid in the isolated rat heart perfused with Krebs solution at a constant flow. Administration of arachidonic acid, 3.3-33 nmol, into the heart caused a small transient increase followed by a pronounced decrease in coronary perfusion pressure and increased myocardial tension, heart rate, and the output of prostaglandins (6-keto-PGF1 alpha, PGE2, and PGF2 alpha). Administration of structurally similar fatty acids, dihomo-gamma-linolenic acid, and 8,14,17-eicosatrienoic acid, produced vasoconstriction and decreased myocardial tension without affecting heart rate or the output of prostaglandins. Infusion of PGI2, PGF2 alpha, or PGE2 produced coronary vasodilation and increased myocardial tension, whereas PGF2 alpha increased heart rate, an effect which was not prevented by propranolol. Indomethacin blocked the effect of arachidonic acid on myocardial tension and heart rate, but only reduced the duration of coronary vasodilation. The initial component of arachidonic acid induced coronary vasodilation which was unaffected by indomethacin and also remained unaltered during the infusion of three structurally dissimilar lipoxygenase inhibitors, eicosatetraynoic acid, nordihydroguaiaretic acid, and 1-phenyl-3-pyrazolidone. Indomethacin did not alter the effects of the exogenously administered prostaglandins on perfusion pressure or myocardial tension; however, it blocked the effect of PGF2 alpha on heart rate. The effect of arachidonic acid or PGF2 alpha to increase heart rate was not blocked by thromboxane synthetase inhibitors, imidazole, or OKY-1581. We conclude that the cardiac effects of arachidonic acid are mediated primarily through its conversion to cyclooxygenase products.(ABSTRACT TRUNCATED AT 250 WORDS)     

Atrial natriuretic factor attenuates the pulmonary pressor response to hypoxia

The influence of endogenous and exogenous atrial natriuretic factor (ANF) on pulmonary hemodynamics was investigated in anesthetized pigs during both normoxia and hypoxia. Continuous hypoxic ventilation with 11% O2 was associated with a uniform but transient increase of plasma immunoreactive (ir) ANF that peaked at 15 min. Plasma irANF was inversely related to pulmonary arterial pressure (Ppa; r = -0.66, P less than 0.01) and pulmonary vascular resistance (PVR; r = -0.56, P less than 0.05) at 30 min of hypoxia in 14 animals; no such relationship was found during normoxia. ANF infusion after 60 min of hypoxia in seven pigs reduced the 156 +/- 20% increase in PVR to 124 +/- 18% (P less than 0.01) at 0.01 microgram.kg-1.min-1 and to 101 +/- 15% (P less than 0.001) at 0.05 microgram.kg-1.min-1. Cardiac output (CO) and systemic arterial pressure (Psa) remained unchanged, whereas mean Ppa decreased from 25.5 +/- 1.5 to 20.5 +/- 15 mmHg (P less than 0.001) and plasma irANF increased two- to nine-fold. ANF infused at 0.1 microgram.kg-1.min-1 (resulting in a 50-fold plasma irANF increase) decreased Psa (-14%) and reduced CO (-10%); systemic vascular resistance (SVR) was not changed, nor was a further decrease in PVR induced. No change in PVR or SVR occurred in normoxic animals at any ANF infusion rate. These results suggest that ANF may act as an endogenous pulmonary vasodilator that could modulate the pulmonary pressor response to hypoxia.     

Macrophage migration inhibitory factor is a cardiac-derived myocardial depressant factor

Macrophage migration inhibitory factor (MIF) is a pluripotent proinflammatory cytokine that is ubiquitously expressed in organs, including the heart. However, no specific role for MIF in modulating cardiac performance has yet been described. Therefore, we examined cardiac MIF expression in mice after LPS challenge (4 mg/kg) and tested the hypothesis that MIF is a mediator of LPS-induced cardiac dysfunction. Western blots of whole heart lysates, as well as immunohistochemistry, documented constitutive MIF protein expression in the heart. Cardiac MIF protein levels significantly decreased after LPS challenge, reaching a nadir at 12 h, and then returned to baseline by 24 h. This pattern was consistent with MIF release from cytoplasmic stores after endotoxin challenge. After release of protein, MIF mRNA levels increased 24-48 h postchallenge. To determine the functional consequences of MIF release, we treated LPS-challenged mice with anti-MIF neutralizing antibodies or isotype control antibodies. Anti-MIF-treated animals had significantly improved cardiac function, as evidenced by a significant improvement in left ventricular (LV) fractional shortening percentage at 8, 12, 24, and 48 h after endotoxin challenge. In support of these findings, perfusion of isolated beating mouse hearts (Langendorff preparation) with recombinant MIF (20 ng/ml) led to a significant decrease in both systolic and diastolic performance [LV pressure (LVP), positive and negative first derivative of LVP with respect to time, and rate of LVP rise at developed pressure of 40 mmHg]. This study demonstrates that MIF mediates LPS-induced cardiac dysfunction and suggests that MIF should be considered a pharmacological target for the treatment of cardiac dysfunction in sepsis and potentially other cardiac diseases.