Cytomegalovirus-Responsive CD8+ T Cells Expand After Solid Organ Transplantation in the Absence of CMV Disease.

Cytomegalovirus (CMV) is a major cause of morbidity and mortality in solid organ transplant recipients. Approximately 60% of adults are CMV seropositive, indicating previous exposure. Following resolution of the primary infection, CMV remains in a latent state. Reactivation is controlled by memory T cells in healthy individuals; transplant recipients have reduced memory T cell function due to chronic immunosuppressive therapies. In this study, CD8+ T cell responses to CMV polypeptides immediate-early-1 and pp65 were analyzed in 16 CMV-seropositive kidney and heart transplant recipients longitudinally pretransplantation and posttransplantation. All patients received standard of care maintenance immunosuppression, antiviral prophylaxis, and CMV viral load monitoring, with approximately half receiving T cell-depleting induction therapy. The frequency of CMV-responsive CD8+ T cells, defined by the production of effector molecules in response to CMV peptides, increased during the course of 1 year posttransplantation. The increase commenced after the completion of antiviral prophylaxis, and these T cells tended to be terminally differentiated effector cells. Based on this small cohort, these data suggest that even in the absence of disease, antigenic exposure may continually shape the CMV-responsive T cell population posttransplantation.

A needleless liquid jet injection delivery method for cardiac gene therapy: a comparative evaluation versus standard routes of delivery reveals enhanced therapeutic retention and cardiac specific gene expression.

This study evaluates needleless liquid jet method and compares it with three common experimental methods: (1) intramuscular injection (IM), (2) left ventricular intracavitary infusion (LVIC), and (3) LV intracavitary infusion with aortic and pulmonary occlusion (LVIC-OCCL). Two protocols were executed. First (n = 24 rats), retention of dye was evaluated 10 min after delivery in an acute model. The acute study revealed the following: significantly higher dye retention (expressed as % myocardial cross-section area) in the left ventricle in both the liquid jet [52 ± 4] % and LVIC-OCCL [58 ± 3] % groups p < 0.05 compared with IM [31 ± 8] % and LVIC [35 ± 4] %. In the second (n = 16 rats), each animal received adeno-associated virus encoding green fluorescent protein (AAV.EGFP) at a single dose with terminal 6-week endpoint. In the second phase with AAV.EGFP at 6 weeks post-delivery, a similar trend was found with liquid jet [54 ± 5] % and LVIC-OCCL [60 ± 8] % featuring more LV expression as compared with IM [30 ± 9] % and LVIC [23 ± 9] %. The IM and LVIC-OCCL cross sections revealed myocardial fibrosis. With more detailed development in future model studies, needleless liquid jet delivery offers a promising strategy to improve direct myocardial delivery.

Pharmacologic pre-conditioning and controlled reperfusion prevent ischemia-reperfusion injury after 30 minutes of hypoxia/ischemia in porcine hearts.

BACKGROUND: Hearts from non-heart-beating organ donors are not transplanted because of risk of ischemia-reperfusion injury. We tested whether pharmacologic pre-conditioning with adenosine and the Na(+)/H(+) exchanger inhibitor, cariporide, combined with controlled reperfusion, would prevent injury in porcine hearts that had sustained 30 minutes of hypoxia/ischemia in closed-chest animals. METHODS: Hearts from Yorkshire pigs (100 kg) were studied in 3 groups. Group 1 (control) hearts were surgically removed while beating. Group 2 hearts were harvested from animals made hypoxic by discontinuing mechanical ventilation for 30 minutes. Group 3 hearts were hypoxic as in Group 2, but these animals received adenosine (40 mg) and cariporide (400 mg) 10 minutes before stopping ventilation. Cardiac function in all groups was assessed ex vivo in a working heart apparatus in which pressure and flow measurements were made over 3 hours. Controlled reperfusion in Group 3 hearts used leukocyte-depleted blood perfusate containing free radical scavengers. Myocardial injury was assessed on the basis of perfusate creatine phosphokinase activity and histopathologically determined injury score. RESULTS: Groups 1 and 3 hearts could be resuscitated to perform work equivalently during the entire reperfusion period and showed positive responses to increases in pre-load and norepinephrine. Group 2 hearts could not perform work. After 3 hours, Group 2 hearts showed significantly higher creatine phosphokinase and histopathologic injury scores compared to with Groups 1 and 3, which were not significantly different from each other. CONCLUSIONS: Pharmacologic pre-conditioning and controlled reperfusion effectively protect non-beating porcine hearts from injury after 30 minutes of hypoxia/ischemia in situ.

Differential regulation of mitogen-activated protein kinases in the failing human heart in response to mechanical unloading.

Background- Mechanical unloading of the heart with a left ventricular assist device (LVAD) leads to favorable changes in the biology of the failing cardiac myocyte. To determine a potential mechanism for these improvements, we examined the regulation of mitogen-activated protein kinases (MAPKs) in the failing heart in the presence and absence of LVAD support. Methods and Results- We examined the degree of activation (ie, phosphorylation) of p44/42 extracellularly regulated kinase, p38 kinase, and c-Jun N-terminal kinase (JNK1/2), and the corresponding activity levels of these MAPKs in myocardial samples obtained from 11 patients with LVAD support and in 11 patients without LVAD support. MAPK activity was also examined in an additional 6 patients from whom paired samples were obtained before and after LVAD support. The activity of p44/42 and JNK1/2 were reduced significantly, whereas p38 activity levels were significantly increased after LVAD support. We examined functional parameters that are linked to MAPK activation, namely cardiac myocyte hypertrophy and apoptosis. Both cardiac myocyte cell size and the incidence of cardiac myocyte apoptosis were significantly reduced after LVAD support. Conclusions- Mechanical unloading of the failing heart leads to differential regulation of MAPKs. These changes in MAPK activity are associated with changes in myocyte hypertrophy and viability, suggesting a potential mechanistic basis for some of the observed salutary changes after LVAD support.

Electrophysiological alterations after mechanical circulatory support in patients with advanced cardiac failure.

BACKGROUND: Recognizing that mechanical circulatory support with a left ventricular assist device (LVAD) induces changes in myocardial structure and contractile function, we examined whether there are changes in ventricular conduction and/or repolarization among failing human hearts after LVAD implantation. METHODS AND RESULTS: We examined 12-lead electrocardiograms before surgery, immediately after LVAD placement, and at a delayed (>1 week) postoperative time point in 23 patients who were receiving LVAD support for refractory heart failure. The immediate effects of hemodynamic unloading via LVAD placement included a decrease in QRS duration from 117+/-6 to 103+/-6 ms (P<0.01), an increase in absolute QT duration from 359+/-6 to 378+/-8 ms (P<0.05), and an increase in the heart rate-corrected QT interval (QTc) from 379+/-10 to 504+/-11 ms (P<0.01). None of these immediate changes were observed among 22 patients undergoing routine coronary artery bypass grafting. With sustained cardiac unloading via LVAD support, there was a marked decrease in the QTc from 504+/-11 to 445+/-9 ms (P<0.001). Studies in isolated cardiac myocytes, obtained at the time of transplantation, confirmed that delayed decreases in heart rate-adjusted QTc were the result of decreases in action potential duration after LVAD support. CONCLUSIONS: Acute electrocardiogram responses to LVAD placement demonstrate the dependence of QRS and QT duration on load in the failing human heart. Delayed decreases in QTc and action potential duration reflect reversal of electrophysiologic remodeling in the failing heart. Shortening of the action potential duration likely contributes to the improved cellular contractile performance observed after sustained LVAD support.

Patients with end-stage congestive heart failure treated with beta-adrenergic receptor antagonists have improved ventricular myocyte calcium regulatory protein abundance.

BACKGROUND: Alterations in Ca(2+)-handling proteins are thought to underlie the deranged Ca(2+) transients that contribute to deterioration of cardiac function in congestive heart failure (CHF). Clinical trials in CHF patients have shown that treatment with beta-adrenergic receptor antagonists (betaB) improves cardiac performance. The present study determined whether the abundance of Ca(2+)-handling proteins is different in failing hearts from patients treated or untreated with beta B. METHODS AND RESULTS: Ca(2+) regulatory protein abundance was compared in LV myocardium of 10 nonfailing hearts (NF group) and 44 failing hearts (CHF group) removed at transplantation. Analysis was performed in betaB-treated (betaB-CHF) and non-betaB treated (non-betaB-CHF) patients and in 4 subgroups: ischemic cardiomyopathy (ICM, n=10), nonischemic dilated cardiomyopathy (DCM, n=10), ICM with betaB therapy (betaB-ICM, n=12), and DCM with betaB therapy (betaB-DCM, n=12). Sarcoplasmic reticulum Ca(2+) ATPase, phospholamban, and Na(+)-Ca(2+) exchanger protein abundance were determined by use of Western blot analysis. Ca(2+) transients were measured with fluo-3. Sarcoplasmic reticulum Ca(2+) ATPase was significantly less abundant whereas phospholamban and Na(+)-Ca(2+) exchanger were not significantly altered in non-betaB-CHF versus NF. Sarcoplasmic reticulum Ca(2+) ATPase in the betaB-ICM and betaB-DCM was greater than in non-betaB-CHF and were not different than in NF. Ca(2+) transients in non-betaB-CHF myocytes had significantly smaller peaks and were prolonged versus NF myocytes. Ca(2+) transients from betaB-CHF myocytes had shorter durations than in betaB-CHF myocytes. CONCLUSIONS: betaB treatment in CHF patients can normalize the abundance of myocyte Ca(2+) regulatory proteins and improve Ca(2+)-handling.

Preserved contractile function despite atrophic remodeling in unloaded rat hearts.

The present study was designed to determine whether myocardial atrophy is necessarily associated with changes in cardiac contractility. Myocardial unloading of normal hearts was produced via heterotopic transplantation in rats. Contractions of isolated myocytes (1.2 mM Ca2+; 37 degrees C) were assessed during field stimulation (0.5, 1.0, and 2.0 Hz), and papillary muscle contractions were assessed during direct stimulation (2.0 mM Ca2+; 37 degrees C; 0.5 Hz). Hemodynamic unloading was associated with a 41% decrease in median myocyte volume and proportional decreases in myocyte length and width. Nevertheless, atrophic myocytes had normal fractional shortening, time to peak contraction, and relaxation times. Despite decreases in absolute maximal force generation (F(max)), there were no differences in F(max)/ area in papillary muscles isolated from unloaded transplanted hearts. Therefore, atrophic remodeling after unloading is associated with intact contractile function in isolated myocytes and papillary muscles when contractile indexes are normalized to account for reductions in cell length and cross-sectional area, respectively. Nevertheless, in the absence of compensatory increases in contractile function, reductions in myocardial mass will lead to impaired overall work capacity.

Ventricular unloading and myocyte recovery: insight gained into the pathophysiology of congestive heart failure.

By unloading the failing myocardium and permitting tissue-based investigations before and after unloading, recent clinical use of ventricular assist devices (VADs) has provided a unique window into the pathophysiology of advanced heart failure in humans. Work to date has provided novel insights into the load-dependent modulation of myocardial hypertrophy, contractility, calcium homeostasis, adrenergic responsiveness, bioenergetics, cytokines, and gene expression. In general, the documented effects of VAD support on the failing heart have been diverse and often dramatic. Moreover, the phenotypic shifts observed have typically tended toward a less pathologic state than that associated with the refractory hypertrophy and heart failure that necessitated VAD implantation. The most striking feature of the composite body of work thus far accumulated in this area is the demonstration that even the most diseased human hearts exhibit the capacity for profound phenotypic plasticity when subjected to sufficient reductions in cardiac loading conditions and neurohormonal stimulation.

Sodium/calcium exchange contributes to contraction and relaxation in failed human ventricular myocytes.

Defects in myocyte contraction and relaxation are key features of human heart failure. Sodium/calcium exchanger-mediated contribution to contraction and relaxation were separated from other mechanisms [L-type calcium current, sarco(endo)plasmic reticulum (SR) Ca(2+)-ATPase] based on voltage, temperature, and selective blockers. Rod-shaped left ventricular myocytes were isolated from failed human explants (n = 29) via perfusion with collagenase-containing Krebs solution. Action potentials using perforated patch and contractions using an edge detector were recorded at 0.5-1.5 Hz in Tyrode solution at 25 degrees C and 37 degrees C. Contraction duration was dependent on action potential (AP) duration at 37 degrees C but not at 25 degrees C, suggesting the role of the exchanger in relaxation and linking myocyte relaxation to the repolarization phase of the AP. Voltage-clamp experiments from -50 to +10 mV for 1,500 ms in Tyrode or Na(+)- and K(+)-free solutions after conditioning pulses triggered biphasic contractions that included a rapid SR-mediated component and a slower voltage-dependent exchanger-mediated component. We used thapsigargin to block the SR, which eliminated the rapid component, and we used an exchanger blocker, Kanebo 7943, which eliminated the slow component. The exchanger was shown to contribute to contraction through reverse-mode exchange, as well as to play a key role in relaxation of human ventricular myocytes.

Physiological significance of early deceleration time prolongation in asymptomatic elderly subjects.

BACKGROUND: Alterations in Doppler-derived diastolic filling patterns are common among elderly persons, but their physiological and prognostic significance remains uncertain, particularly in asymptomatic older persons without overt cardiac disease. This study was designed to determine whether early mitral inflow deceleration time (DT) prolongation is of physiological significance in asymptomatic elderly subjects. METHODS AND RESULTS: In 15 asymptomatic patients aged 60 to 93 years with no history of heart failure (HF) or edema, we performed two-dimensional and Doppler echocardiography and 60-minute head-out, isothermic water immersion to produce circulatory volume expansion. Plasma levels of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were measured immediately before and after water immersion. Seven of 15 patients had a normal mitral early DT (160 to 240 milliseconds; group 1) and 8 of 15 patients had DT prolongation (> 240 milliseconds; group 2). Group 2 subjects had significantly smaller chamber sizes and increased relative wall thickness without increased left ventricular mass. Head-out water immersion produced greater increases in plasma ANP levels in group 2 subjects with longer DTs despite similar degrees of circulatory volume expansion in each group. In contrast, plasma BNP levels did not increase significantly with water immersion in either group. CONCLUSION: Early DT prolongation in asymptomatic elderly subjects is associated with increased relative wall thickness and enhanced ANP increments after central volume expansion. Such exaggerated responses suggest that, in the elderly, a prolonged DT has physiological significance and may represent a precursor to symptomatic diastolic HF, a condition known to be associated with advancing age.

The sarcoplasmic reticulum and the Na+/Ca2+ exchanger both contribute to the Ca2+ transient of failing human ventricular myocytes.

Our objective was to determine the respective roles of the sarcoplasmic reticulum (SR) and the Na+/Ca2+ exchanger in the small, slowly decaying Ca2+ transients of failing human ventricular myocytes. Left ventricular myocytes were isolated from explanted hearts of patients with severe heart failure (n=18). Cytosolic Ca2+, contraction, and action potentials were measured by using indo-1, edge detection, and patch pipettes, respectively. Selective inhibitors of SR Ca2+ transport (thapsigargin) and reverse-mode Na+/Ca2+ exchange activity (No. 7943, Kanebo Ltd) were used to define the respective contribution of these processes to the Ca2+ transient. Ca2+ transients and contractions induced by action potentials (AP transients) at 0.5 Hz exhibited phasic and tonic components. The duration of the tonic component was determined by the action potential duration. Ca2+ transients induced by caffeine (Caf transients) exhibited only a phasic component with a rapid rate of decay that was dependent on extracellular Na+. The SR Ca2+-ATPase inhibitor thapsigargin abolished the phasic component of the AP Ca2+ transient and of the Caf transient but had no significant effect on the tonic component of the AP transient. The Na+/Ca2+ exchange inhibitor No. 7943 eliminated the tonic component of the AP transient and reduced the magnitude of the phasic component. In failing human myocytes, Ca2+ transients and contractions exhibit an SR-related, phasic component and a slow, reverse-mode Na+/Ca2+ exchange-related tonic component. These findings suggest that Ca2+ influx via reverse-mode Na+/Ca2+ exchange during the action potential may contribute to the slow decay of the Ca2+ transient in failing human myocytes.

Regression of cellular hypertrophy after left ventricular assist device support.

BACKGROUND: Although multiple studies have shown that the left ventricular assist device (LVAD) improves distorted cardiac geometry, the pathological mechanisms of the "reverse remodeling" of the heart are unknown. Our goal was to determine the effects of LVAD support on cardiac myocyte size and shape. METHODS AND RESULTS: Isolated myocytes were obtained at cardiac transplantation from 30 failing hearts (12 ischemic, 18 nonischemic) without LVAD support, 10 failing hearts that received LVAD support for 75+/-15 days, and 6 nonfailing hearts. Cardiac myocyte volume, length, width, and thickness were determined by use of previously validated techniques. Isolated myocytes from myopathic hearts exhibited increased volume, length, width, and length-to-thickness ratio compared with normal myocytes (P<0.05). However, there were no differences in any parameter between myocytes from ischemic and nonischemic cardiomyopathic hearts. Long-term LVAD support resulted in a 28% reduction in myocyte volume, 20% reduction in cell length, 20% reduction in cell width, and 32% reduction in cell length-to-thickness ratio (P<0.05). In contrast, LVAD support was associated with no change in cell thickness. These cellular changes were associated with reductions in left ventricular dilation and left ventricular mass measured echocardiographically in 6 of 10 LVAD-supported patients. CONCLUSIONS: These studies suggest that the regression of cellular hypertrophy is a major contributor to the "reverse remodeling" of the heart after LVAD implantation. The favorable alterations in geometry that occur in parallel fashion at both the organ and cellular levels may contribute to reduced wall stress and improved mechanical performance after LVAD support.

Contribution of reverse-mode sodium-calcium exchange to contractions in failing human left ventricular myocytes.

OBJECTIVE: To examine the contribution of reverse mode sodium-calcium (Na-Ca) exchange to contractions in isolated left-ventricular myocytes from failing human heart. METHODS: Low resistance patch pipettes were used to dialyze cells with Na-free or high-Na pipette solution ([Na]pipette = 0 and 20 mmol/L, respectively) to reduce or enhance Na-Ca exchange. Whole-cell membrane-potential, membrane-current and cell-shortening data were simultaneously acquired during whole-cell voltage clamp protocols. Thapsigargin (100 nmol/L) and nifedipine (1 mumol/L) were also used to inhibit sarcoplasmic reticulum (SR) Ca-ATPase and L-type Ca channels, respectively. RESULTS: Two types of contractions were observed. Rapid phasic contractions were seen in both Na-free and high-Na cells. Slow tonic contractions were seen only in high-Na cells. Phasic contractions demonstrated bell-shaped voltage dependence over the voltage range that corresponds to the activity of the L-type Ca channel. Although the voltage dependence of phasic contractions were similar Na-free and high-Na cells, phasic contractions in high-Na cells were larger than phasic contractions in Na-free cells. Phasic contractions were sensitive to inhibition of SR Ca-ATPase and L-type Ca channels. Tonic contractions were not inhibited by either thapsigargin or nifedipine. In thapsigargin-treated high-Na cells, tonic contraction magnitude increased exponentially with test-potential. CONCLUSIONS: The increases in phasic contraction magnitude observed in high-Na cells compared to Na-free cells were most likely due to increased SR Ca loading resulting from increased reverse-mode Na-Ca exchange. Our results also suggest that tonic contractions in high-Na cells were mediated by Ca entry via reverse-mode Na-Ca exchange and were not the result of either SR Ca release or L-type Ca channel activity.

Myocyte recovery after mechanical circulatory support in humans with end-stage heart failure.

BACKGROUND: The failing myocardium is characterized by decreased force production, slowed relaxation, and depressed responses to beta-adrenergic stimulation. In some heart failure patients, heart function is so poor that a left ventricular assist device (LVAD) is inserted as a bridge to transplantation. In the present research, we investigated whether circulatory support with an LVAD influenced the functional properties of myocytes from the failing heart. METHODS AND RESULTS: Myocytes were isolated from human explanted failing hearts (HF-myocytes) and failing hearts with antecedent LVAD support (HF-LVAD-myocytes). Studies of myocyte function indicated that the magnitude of contraction was greater (9.6+/-0.7% versus 6.9+/-0.5% shortening), the time to peak contraction was significantly abbreviated (0.37+/-0.01 versus 0.75+/-0.04 seconds), and the time to 50% relaxation was reduced (0.55+/-0.02 versus 1.45+/-0.11 seconds) in the HF-LVAD-myocytes compared with the HF-myocytes (P<0.05). The HF-LVAD-myocytes had larger contractions than the HF-myocytes at all frequencies of stimulation tested. The negative force-frequency relationship of the HF-myocytes was improved in HF-LVAD-myocytes but was not reversed. Responses to beta-adrenergic stimulation (by isoproterenol) were greater in HF-LVAD-myocytes versus HF-myocytes. CONCLUSIONS: The results of the study strongly support the idea that circulatory support with an LVAD improves myocyte contractile properties and increases beta-adrenergic responsiveness.

Altered myocardial phenotype after mechanical support in human beings with advanced cardiomyopathy.

BACKGROUND: Left ventricular assist devices (LVAD) provide lifesaving circulatory support to patients awaiting heart transplantation. To date, the extent to which sustained mechanical unloading alters the phenotype of pathologic myocardial hypertrophy in dilated cardiomyopathy is unknown. METHODS: We examined left ventricular size, myocyte and myocardial immunoreactivity for atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in eight patients with advanced dilated cardiomyopathy before and after LVAD support. The mean duration of congestive heart failure was 18 +/- 5 months, and LVAD support averaged 42 +/- 4 days before heart transplantation. RESULTS: Echocardiographically determined left ventricular mass decreased from 505 +/- 83 to 297 +/- 52 gm (p < 0.05) during LVAD support, whereas minimum myocyte diameter decreased from 28.1 +/- 0.9 to 21.7 +/- 0.6 microns (p < 0.01) in transmural myocardial tissue specimens. Overall left ventricular ANP immunopositivity decreased from 48% at LVAD placement to 12% at transplantation (p < 0.05), whereas BNP immunopositivity decreased from 28% to 4% after LVAD support. Moreover, a gradient of ANP and BNP immunostaining from subendocardium to epicardium observed before mechanical unloading diminished after LVAD support. Analysis of the relationship between left ventricular mass and ANP immunopositivity revealed a close and highly significant correlation between these variables. CONCLUSIONS: These studies demonstrate remarkable left ventricular plasticity even in the presence of advanced cardiomyopathy. Parallel reductions in myocardial mass and myocyte size with reductions in ventricular ANP and BNP immunostaining indicate a novel regression of the phenotype of pathologic hypertrophy within the human myocardium after LVAD support.

Donor-specific HLA antibodies after transplantation are associated with deterioration in cardiac function.

Although there is increasing evidence that mismatched donor HLA antigens are associated with a lowering of survival of human cardiac allografts, the effect of antibodies that bind those antigens is less clear. The existence of lymphocytotoxic antibodies prior to cardiac transplantation has been associated with a poor outcome in the majority of reports of relevant studies, as has their appearance post-transplantation. But how such antibodies, especially those with HLA specificity, cause poor outcomes has been poorly understood. The purpose of this study was to investigate the effect of anti-HLA antibodies appearing in the circulation after human orthotopic heart transplantation. Such antibodies were identified by a standard microlymphocytotoxicity technique using panels of frozen lymphocytes from normal donors who had been tissue typed. Of 74 patients transplanted over a 12-month period, 4 (5.4%) developed alloantibodies specific for mismatched donor HLA antigens. The first patient developed antibodies to HLA-A23 and B44 together with poor ventricular function and vascular rejection requiring retransplantation within 4 months. The other patients (3) developed antibodies specific for HLA-DQ antigens and experienced variable numbers of episodes of cellular rejection with no evidence of vascular rejection on endomyocardial biopsy. Two of these three patients died (8 and 11 months post-transplant) after three and six rejection episodes, respectively. The one surviving patient had seven rejection episodes and continues to have poor ventricular function 18 months post-transplant. We conclude that alloantibodies specific for mismatched donor HLA antigens may have a deleterious effect on the outcome of the human cardiac allograft and should be monitored closely post-transplant. Furthermore, such antibodies may mediate effects on the transplanted heart which are not detectable in specimens obtained by endomyocardial biopsy.

Functional and morphologic adaptation of undersized donor hearts after heart transplantation.

OBJECTIVES: This study analyzes our experience with transplantation of small donor hearts in a subgroup of moribund patients who could not be bridged to transplantation with mechanical assist devices. BACKGROUND: The major problem facing transplant programs in the United States is the lack of donor heart availability. One method of expanding the donor pool may be to liberalize the criteria for an acceptable donor heart. METHODS: We analyzed the growth and adaptation of 14 undersized and 14 conventionally sized donor hearts over a period of 10 weeks after heart transplantation. The left ventricular systolic and diastolic diameters, septal and posterior wall thicknesses, left ventricular mass calculated by the Penn convention and left ventricular ejection fraction were obtained by M-mode and two-dimensional echocardiography and documented by a single reader in blinded manner. Echocardiographic measurements were obtained before implantation and at 5 and 10 weeks after orthotopic heart transplantation. RESULTS: The mean (+/- SD) donor/recipient weight ratios were 0.53 +/- 0.06 for undersized hearts and 0.98 +/- 0.05 for normal-sized hearts. All 28 patients received similar immunosuppressive regimens, including intravenous steroids, cyclosporine and azathioprine. The length of hospital stay after transplantation did not vary significantly between the two groups. All the patients had at least one rejection episode during the 10-week study period. There was a tendency toward higher pulmonary pressures in undersized hearts, which was not statistically significant. Heart rate was significantly higher for undersized hearts, due in part to the use of theophylline or terbutaline to maintain tachycardia. There was a significant increase in left ventricular systolic and diastolic dimensions in undersized hearts compared with conventionally sized hearts. Undersized hearts increased in left ventricular mass over the 10-week period, whereas the conventionally sized donor hearts did not change between 5 and 10 weeks. CONCLUSIONS: In undersized hearts the increase in left ventricular mass and internal dimensions, with preservation of the posterior/septal wall thickness ratio, suggests that the left ventricle adapts to the larger recipient circulation early after transplantation. Despite denervation and a mismatched load, undersized transplanted hearts adapt appropriately to their new hemodynamic milieu.

The role of neutral endopeptidase in dogs with evolving congestive heart failure.

BACKGROUND: Recent studies suggest that neurohumoral mechanisms including decreased renal responses to increases in atrial natriuretic factor (ANF) play a central role in the progression from asymptomatic cardiac dysfunction to advanced congestive heart failure (CHF) with sodium retention, vasoconstriction, and reduced exercise tolerance. Recognizing that neutral endopeptidase 24.11 degrades ANF and may be enhanced in CHF, we hypothesized that chronic neutral endopeptidase inhibition (NEP-I) would potentiate renal responses to exogenous ANF and alter the temporal evolution of sodium retention in evolving CHF by potentiation of increased endogenous ANF. METHODS AND RESULTS: We studied 13 conscious dogs with evolving CHF produced by rapid ventricular pacing at 250 beats per minute. Six of these dogs received NEP-I with candoxatril, 10 mg/kg PO BID, throughout evolving CHF. Responses to exogenous ANF, 10 micrograms/kg IV bolus, were assessed at baseline and after 6 days of CHF. Daily metabolic studies during evolving CHF with chronic NEP-I showed increased sodium excretion and renal cGMP generation consistent with enhanced renal activity of endogenous ANF compared with untreated controls. In addition, renal natriuretic and cGMP responses to exogenous ANF were intact in CHF with chronic NEP-I in contrast to markedly attenuated renal responses to exogenous ANF in untreated CHF. Despite enhanced ANF responsiveness and improved sodium balance in evolving CHF, a moderate degree of sodium retention was observed during chronic NEP-I in evolving CHF. CONCLUSIONS: Enzymatic degradation by neutral endopeptidase limits local renal responses to increases in endogenous and exogenous ANF in CHF independent of changes in systemic hemodynamics or augmented plasma concentrations of ANF. The moderate sodium retention observed during evolving CHF despite chronic NEP-I probably reflects the antinatriuretic effects of hemodynamic and humoral factors independent of ANF activity.

Role of endothelin receptor subtypes in the in vivo regulation of renal function.

Endothelin (ET) is a potent vasoconstrictor peptide of endothelial origin, which at low doses results in renal vasoconstriction and diuresis with variable actions on sodium excretion. The current study conducted in four groups of anesthetized dogs was designed to define the role of the ETA and ETB receptor subtypes in the renal actions of low-dose exogenous ET. Group 1 (n = 4) animals served as time controls. In group 2 (n = 6) a systemic ET-1 (5 ng.kg-1.min-1) infusion mediated renal vasoconstriction, antinatriuresis with increases in proximal fractional reabsorption of sodium, and diuresis with a decrease in urine osmolality. In group 3 (n = 6) intrarenal BQ-123 (4 micrograms.kg-1.min-1), a selective ETA antagonist, abolished the systemic ET-1-mediated changes in renal hemodynamics and unmasked a natriuretic action at the level of the proximal tubule. In contrast, the diuretic response of ET was not altered by BQ-123. In group 4 (n = 6) intrarenal sarafotoxin 6-c, a selective ETB receptor agonist, resulted in a diuretic response without a change in sodium excretion. These studies suggest that the ETA receptor contributes to the renal vasoconstriction, whereas the ETB receptor is largely responsible for the diuretic response during exogenous ET. This study also suggests that at low doses ET is natriuretic in vivo by decreasing proximal tubular reabsorption of sodium independent of ETA or ETB receptor activation.

Inhibition of cyclic GMP phosphodiesterases augments renal responses to atrial natriuretic factor in congestive heart failure.

Atrial natriuretic factor (ANF), a cardiac peptide hormone with potent natriuretic and vasodilator actions, mediates its biologic responses via increases in intracellular cyclic guanosine monophosphate (cGMP). Recognizing that phosphodiesterases degrade cGMP and that congestive heart failure (CHF) is characterized by reduced renal responses to ANF, the authors hypothesized that cGMP phosphodiesterases limit the renal actions of exogenous and endogenous ANF in the presence of experimental CHF. In anesthetized dogs with severe CHF and avid sodium retention produced by rapid ventricular pacing, the authors explored the renal actions of M&B 22,948 (Rhône-Poulenc, Essex, UK), an inhibitor of cGMP-specific phosphodiesterases. High-dose intrarenal cGMP phosphodiesterase inhibition (PDI), with minimal effects upon systemic hemodynamics and hormones, significantly enhanced sodium excretion. This occurred primarily by decreasing distal nephron sodium reabsorption while enhancing renal cGMP generation. In separate groups of dogs, low-dose intrarenal cGMP PDI potentiated the actions of exogenous ANF on glomerular filtration and distal nephron sodium reabsorption, leading to enhanced natriuresis in the presence or absence of severe CHF. These studies support a link between ANF and the renal actions of cGMP PDI, and indicate that cGMP phosphodiesterases may contribute to sodium retention in advanced CHF by limiting the renal actions of increased endogenous ANF.