Imputation of class I and II HLA loci using high-density SNPs from ImmunoChip and their associations with Kawasaki disease in family-based study.

Kawasaki disease (KD) is the leading cause of acquired heart disease in children in most developed countries including the United States. The etiology of KD is not known; however, epidemiological and immunological data suggest infectious or immune-related factors in the manifestation of the disease. Further, KD has several hereditary features that strongly suggest a genetic component to disease pathogenesis. Human leucocyte antigen (HLA) loci have also been reported to be associated with KD, but results have been inconsistent, in part, because of small study samples and varying linkage disequilibrium (LD) patterns observed across different ethnic groups. To maximize the informativeness of single nucleotide polymorphism (SNP) genotypes in the major histocompatibility (MHC) region, we imputed classical HLA I (A, B, C) and HLA II (DRB1, DQA1, DQB1) alleles using SNP2HLA method from genotypes of 6700 SNPs within the extended MHC region contained in the ImmunoChip among 112 White patients with KD and their biological parents from North America and tested their association with KD susceptibility using the transmission disequilibrium test. Mendelian consistency in the trios suggested high accuracy and reliability of the imputed alleles (class I = 97.5%, class II = 96.6%). While several SNPs in the MHC region were individually associated with KD susceptibility, we report over-transmission of HLA-C*15 (z = +2.19, P = 0.03) and under-transmission of HLA-B*44 (z = -2.49, P = 0.01) alleles from parents to patients with KD. HLA-B*44 has been associated with KD in other smaller studies, and both HLA-C*15 and HLA-B*44 have biological mechanisms that could potentially be involved in KD pathogenesis. Overall, inferring HLA loci within the same ethnic group, using family-based information is a powerful approach. However, studies with larger sample sizes are warranted to evaluate the correlations of the strength and directions between the SNPs in MHC region and the imputed HLA alleles with KD.

High-density genotyping of immune loci in Kawasaki disease and IVIG treatment response in European-American case-parent trio study.

Kawasaki disease (KD) is a diffuse and acute small-vessel vasculitis observed in children, and has genetic and autoimmune components. We genotyped 112 case-parent trios of European decent (confirmed by ancestry informative markers) using the immunoChip array, and performed association analyses with susceptibility to KD and intravenous immunoglobulin (IVIG) non-response. KD susceptibility was assessed using the transmission disequilibrium test, whereas IVIG non-response was evaluated using multivariable logistic regression analysis. We replicated single-nucleotide polymorphisms (SNPs) in three gene regions (FCGR, CD40/CDH22 and HLA-DQB2/HLA-DOB) that have been previously associated with KD and provide support to other findings of several novel SNPs in genes with a potential pathway in KD pathogenesis. SNP rs838143 in the 3'-untranslated region of the FUT1 gene (2.7 × 10(-5)) and rs9847915 in the intergenic region of LOC730109 | BRD7P2 (6.81 × 10(-7)) were the top hits for KD susceptibility in additive and dominant models, respectively. The top hits for IVIG responsiveness were rs1200332 in the intergenic region of BAZ1A | C14orf19 (1.4 × 10(-4)) and rs4889606 in the intron of the STX1B gene (6.95 × 10(-5)) in additive and dominant models, respectively. Our study suggests that genes and biological pathways involved in autoimmune diseases have an important role in the pathogenesis of KD and IVIG response mechanism.

Triidothyronine and epinephrine rapidly modify myocardial substrate selection: a (13)C isotopomer analysis.

Triiodothyronine (T(3)) exerts direct action on myocardial oxygen consumption (MVO(2)), although its immediate effects on substrate metabolism have not been elucidated. The hypothesis, that T(3) regulates substrate selection and flux, was tested in isovolumic rat hearts under four conditions: control, T(3) (10 nM), epinephrine (Epi), and T(3) and Epi (TE). Hearts were perfused with [1,3-(13)C]acetoacetic acid (AA, 0.17 mM), L-[3-(13)C]lactic acid (LAC, 1.2 mM), U-(13)C-labeled long-chain free fatty acids (FFA, 0.35 mM), and unlabeled D-glucose (5.5 mM) for 30 min. Fractional acetyl-CoA contribution to the tricarboxylic acid cycle (Fc) per substrate was determined using (13)C NMR and isotopomer analysis. Oxidative fluxes were calculated using Fc, the respiratory quotient, and MVO(2). T(3) increased (P < 0.05) Fc(FFA), decreased Fc(LAC), and increased absolute FFA oxidation from 0.58 +/- 0.03 to 0.68 +/- 0.03 micromol. min(-1). g dry wt(-1) (P < 0.05). Epi decreased Fc(FFA) and Fc(AA), although FFA flux increased from 0.58 +/- 0.03 to 0.75 +/- 0.09 micromol. min(-1). g dry wt(-1). T(3) moderated the change in Fc(FFA) induced by Epi. In summary, T(3) exerts direct action on substrate pathways and enhances FFA selection and oxidation, although the Epi effect dominates at a high work state.

Human cardiac myosin heavy chain isoforms in fetal and failing adult atria and ventricles.

The goal of this study was to test the hypothesis that the relative amounts of the cardiac myosin heavy chain (MHC) isoforms MHC-alpha and MHC-beta change during development and transition to heart failure in the human myocardium. The relative amounts of MHC-alpha and MHC-beta in ventricular and atrial samples from fetal (gestational days 47--110) and nonfailing and failing adult hearts were determined. The majority of the fetal right and left ventricular samples contained small relative amounts of MHC-alpha (mean < 5% of total MHC). There was a small significant decrease in the level of MHC-alpha in the ventricles between 7 and 12 wk of gestation. Fetal atria expressed predominantly MHC-alpha (mean > 95%), with MHC-beta being detected in most samples. The majority of adult nonfailing right and left ventricular samples had detectable levels of MHC-alpha ranging from 1 to 10%. Failing right and left ventricles expressed a significantly lower level of MHC-alpha. MHC-alpha comprised approximately 90% of the total MHC in adult nonfailing left atria, whereas the relative amount of MHC-alpha in the left atria of individuals with dilated or ischemic cardiomyopathy was approximately 50%. The differences in MHC isoform composition between fetal and nonfailing adult atria and between fetal and nonfailing adult ventricles were not statistically significant. We concluded that the MHC isoform compositions of fetal human atria are the same as those of nonfailing adult atria and that the ventricular MHC isoform composition is different between adult nonfailing and failing hearts. Furthermore, the marked alteration in atrial MHC isoform composition, associated with cardiomyopathy, does not represent a regression to a pattern that is uniquely characteristic of the fetal stage.

HOE-642 (cariporide) alters pH(i) and diastolic function after ischemia during reperfusion in pig hearts in situ.

The specific Na(+)/H(+) exchange inhibitor HOE-642 prevents ischemic and reperfusion injury in the myocardium. Although this inhibitor alters H(+) ion flux during reperfusion in vitro, this action has not been confirmed during complex conditions in situ. Myocardial intracellular pH (pH(i)) and high-energy phosphates were monitored using (31)P magnetic resonance spectroscopy in open-chest pigs supported by cardiopulmonary bypass during 10 min of ischemia and reperfusion. Intravenous HOE-642 (2 mg/kg; n = 8) administered before ischemia prevented the increases in diastolic stiffness noted in control pigs (n = 8), although it did not alter the postischemic peak-elastance or pressure-rate product measured using a distensible balloon within the left ventricle. HOE-642 induced no change in pH(i) during ischemia but caused significant delays in intracellular realkalinization during reperfusion. HOE-642 did not alter phosphocreatine depletion and repletion but did improve ATP preservation. Na(+)/H(+) exchange inhibition through HOE-642 delays intracellular alkalinization in the myocardium in situ during reperfusion in association with improved diastolic function and high-energy phosphate preservation.

Major coronary artery anomalies in a pediatric population: incidence and clinical importance.

OBJECTIVES: We sought to prospectively determine the incidence and clinical significance of major coronary artery anomalies in asymptomatic children using transthoracic two-dimensional echocardiography. BACKGROUND: Anomalous origins of the left main coronary artery (ALMCA) from the right sinus of Valsalva or anomalous origins the right coronary artery (ARCA) from the left sinus are rarely diagnosed in children and can cause sudden death, especially in young athletes. Because most patients are asymptomatic, the diagnosis is often made post mortem. No study to date has prospectively identified anomalous coronary arteries in asymptomatic children in the general population. METHODS: After serendipitously identifying an index case with ALMCA, we examined proximal coronary artery anatomy in children with otherwise anatomically normal hearts who were referred for echocardiography. In those diagnosed with ALMCA or ARCA, we performed further tests. RESULTS: Within a three-year period, echocardiograms were obtained in 2,388 children and adolescents. Four children (0.17%) were identified with anomalous origin of their coronary arteries, and angiograms, exercise perfusion studies and/or stress tests were then performed. One ARCA patient had decreased perfusion in the right coronary artery (RCA) perfusion area and showed ventricular ectopy on electrocardiogram (ECG) at rest that diminished but did not resolve with exercise. A second patient with ALMCA had atrial tachycardia immediately after exercise, with inferior and lateral ischemic changes on ECG and frequent junctional and/or ventricular premature complexes both at rest and recovery. CONCLUSIONS: This study demonstrates that although anomalous origins of coronary arteries are rare in asymptomatic children, the prevalence is greater than that found in other prospective studies. Ischemia can occur with both ALMCA and ARCA even though patients remain asymptomatic. Because of the high risk of sudden cardiac death, aggressive surgical management and close follow-up are necessary.

Thyroid hormone coordinates respiratory control maturation and adenine nucleotide translocator expression in heart in vivo.

BACKGROUND: The signal transduction mechanism linking mitochondrial ATP synthesis with cytosolic ATP utilization in heart changes during postnatal development in vivo. This maturational process occurs in parallel with accumulation of mitochondrial adenine nucleotide translocator (ANT), which provides a possible site for respiratory control. We postulated that thyroid hormone regulates these maturational processes. METHODS AND RESULTS: We used (31)P MR spectroscopy to determine the relationship between myocardial high-energy phosphates, phosphocreatine, and ADP and oxygen consumption (MVO(2)) during epinephrine stimulation in 32- to 40-day-old lambs thyroidectomized after birth (THY) and age-matched controls. Steady-state protein and mRNA levels for ANT isoforms and beta-F(1)-ATPase were assessed from left ventricular tissues by Western and Northern blotting. With greater doses of epinephrine, THY attained lower peak MVO(2) than controls (P:<0.05). Controls maintained high-energy phosphate levels, unlike THY, which demonstrated significantly decreased phosphocreatine/ATP and increased cytosolic ADP despite lower peak MVO(2). No significant differences in beta-F(1)-ATPase protein or mRNA occurred between groups. However, ANT isoform mRNA levels were 2-fold greater and protein levels 4-fold greater in control hearts. CONCLUSIONS: These data imply that the maturational shift away from ADP-mediated respiratory control is regulated by thyroid hormone in vivo. Specific thyroid-modulated increases in ANT mRNA and protein imply that this regulation occurs in part at a pretranslational level.

Triiodothyronine repletion in infants during cardiopulmonary bypass for congenital heart disease.

OBJECTIVE: Cardiopulmonary bypass suppresses circulating thyroid hormone levels. Although acute triiodothyronine repletion has been evaluated in adult patients after cardiopulmonary bypass, triiodothyronine pharmacokinetics and effects have not previously been studied in infants undergoing operations for congenital heart disease. We hypothesized that triiodothyronine deficiency in the developing heart after bypass may adversely affect cardiac function reserve postoperatively. METHODS: Infants less than 1 year old undergoing ventricular septal defect or tetralogy of Fallot repair were randomized into 2 groups. Group T (n = 7) received triiodothyronine (0.4 microg/kg) immediately before the start of cardiopulmonary bypass and again with myocardial reperfusion. Control (NT, n = 7) patients received saline solution placebo or no treatment. RESULTS: These groups underwent similar ischemic and bypass times and received similar quantities of inotropic agents after the operation. The NT group demonstrated significant depression in circulating levels, compared with prebypass levels, for free triiodothyronine and total triiodothyronine at 1, 24, and 72 hours after bypass. Group T demonstrated similar low thyroxine values, but free and total triiodothyronine levels were maintained at prebypass levels for 24 hours and remained elevated over those of group NT (P <.05) at 72 hours. Heart rate was transiently elevated in group T compared with group NT (P <.05), and peak systolic pressure-rate product increased after 6 hours. CONCLUSION: These data imply that (1) triiodothyronine in the prescribed dose prevents circulating triiodothyronine deficiencies and (2) triiodothyronine repletion promotes elevation in heart rate without concomitant decrease in systemic blood pressure. Elevation of peak systolic pressure-rate product implies that triiodothyronine repletion improves myocardial oxygen consumption and may enhance cardiac function reserve after cardiopulmonary bypass in infants.

Signaling and expression for mitochondrial membrane proteins during left ventricular remodeling and contractile failure after myocardial infarction.

OBJECTIVES: This study was conducted to test hypotheses stating that: 1) altered signaling for mitochondrial membrane proteins occurs during postinfarction remodeling, and 2) successful myocardial adaptation relates to promotion of specific mitochondrial membrane components. BACKGROUND: Abnormalities in high-energy phosphate content and limitations in adenosine 5'-triphosphate (ATP) synthesis rate occur during the transition to contractile failure from compensatory remodeling after left ventricular infarction. The adenine nucleotide translocator (ANT) and F1-ATPase respectively regulate mitochondrial adenosine 5'-diphosphate (ADP)/ATP exchange and ADP-phosphorylation, which are key components of high-energy phosphate metabolism. METHODS: Steady-state mRNA and protein expression for ANT isoform1 and the beta subunit of the F1-ATPase (betaF1) were analyzed in myocardium remote from the infarction zone eight weeks after left circumflex coronary artery ligation in pigs, demonstrating either successful left ventricular remodeling (LVR, n = 8) or congestive heart failure (CHF, n = 4) as determined by clinical and contractile performance parameters. RESULTS: Substantial reductions in steady-state mRNA expression for ANT1 and betaF1 relative to normal (n = 8) occur in CHF, p < 0.01, but not in LVR. Relative expression for both proteins coordinated with their respective steady-state mRNA levels; CHF at 40% normal, p < 0.05 for ANT and 70% normal for betaF1, p < 0.05. CONCLUSIONS: Maintained signaling for major mitochondrial membrane proteins occurs in association with successful remodeling and adaptation after infarction. Reduced expression of these proteins relates to limited ATP synthesis capacity and high energy phosphate kinetic abnormalities previously demonstrated in CHF. These findings imply that mitochondrial processes participate in myocardial remodeling after infarction.

Corrected QT interval (QTc) prolongation and syncope associated with pseudohypoparathyroidism and hypocalcemia.

An adolescent presented with exercise-associated syncope and electrocardiographic corrected QT interval (QTc) prolongation. Pseudohypoparathyroidism-induced hypocalcemia was diagnosed. The QTc (485 to 505 milliseconds) shortened during normalization of calcium levels, and syncope has not reoccurred.

Mitochondrial protein and HSP70 signaling after ischemia in hypothermic-adapted hearts augmented with glucose.

Hypothermia improves resistance to subsequent ischemia in the cardioplegic-arrested heart (CAH). This adaptive process produces mRNA elevation for heat shock protein (HSP) 70-1 and mitochondrial proteins, adenine nucleotide translocator (ANT(1)), and beta-F(1)-ATPase. Glucose in cardioplegia also enhances myocardial protection. These processes might be linked to reduced ATP depletion. To assess for synergism between these protective processes, isolated rabbit hearts (n = 91) were perfused at 37 degrees C and exposed to ischemic cardioplegic arrest for 2 h. Hearts were in four groups: control (C), hypothermia adapted (H) perfused to 31 degrees C 20 min before ischemia, 22 mM glucose (G) in cardioplegia, and hypothermic adaptation and glucose (HG). Developed pressure (DP), dP/dt(max), and pressure-rate product (PRP) improved (P < 0.05) in G, H, and HG compared with C during reperfusion. DP and PRP were elevated in HG over H and G. ATP was higher in G, H, and HG, although no additional increase in HG over H was found. Lactate and CO(2) production were elevated in G only. The mRNA expression for HSP70-1, ANT(1), and beta-F(1)-ATPase was elevated severalfold in H and HG, but not G over C during reperfusion. In conclusion, glucose provides additional functional improvement in H. Additionally, neither ATP levels nor anaerobic metabolism are linked to mRNA expression for HSP70, ANT(1), or beta-F(1)-ATPase in CAH.

Maturational changes in gene expression for adenine nucleotide translocator isoforms and betaF1-ATPase in rabbit heart.

Maturational changes in myocardial respiratory control have been related to postnatal accumulation of adenine nucleotide translocator (ANT) in the inner mitochondrial membrane. Alternatively alterations in relative isoform distribution for this nuclear-encoded gene during myocardial maturation might be responsible for changing the kinetics of respiratory control. Rabbit hearts were analyzed for adenine nucleotide translocator isoform (ANT1, ANT2, ANT3) gene expression and distribution at four ages (fetal, 29/31 days of gestation; 1 h postnatal; 9 days postnatal; and 3-4 months postnatal). Transcript levels for the coordinately expressed betaF1-ATPase were also examined in these hearts. These studies demonstrated that mRNA expression for ANT1 in coordination with betaF1-ATPase increased substantially after 9 days of age in rabbit hearts. Expression of the minor isoform ANT3 parallels ANT1, though no change in expression of the kidney-specific isoform ANT2 occurs in heart during this developmental period. Previous work has demonstrated that ANT protein accumulation is closely coordinated with mRNA expression for ANT1. These results support previous studies, which indicate that the operational mode of myocardial respiratory control depends on adenine nucleotide mRNA expression. Changes in relative adenine nucleotide translocator isoform distribution do occur during fetal to mature transition and may contribute to observed changes in the mode of respiratory control.

Temperature threshold and preservation of signaling for mitochondrial membrane proteins during ischemia in rabbit heart.

Temperature modulates both myocardial energy requirements and production. We have previously demonstrated that myocardial protection induced by hypothermic adaptation preserves expression of genes regulating heat shock protein and the nuclear-encoded mitochondrial proteins, the adenine nucleotide translocator isoform 1 (ANT1), and the beta subunit of F1-ATPase (beta F1-ATPase). This preservation is associated with a reduction in ATP depletion similar to that noted in cardioplegic arrested hearts preserved at a critical temperature (30 degrees C) or below. We tested the hypothesis that expression of these genes may also be subject to this temperature threshold phenomenon. Isolated perfused rabbit hearts were subjected to ischemic cardioplegic arrest at 4, 30, or 34 degrees C for 120 min. Cardiac function indices and steady-state mRNA levels for ANT1, beta F1-ATPase, and HSP70-1 were measured prior to ischemia (B) and after 45 min of reperfusion. Cardiac function was significantly depressed in the 34 degrees C group. Ischemia at 34 degrees C reduced steady-state mRNA levels for ANT1 and beta F1-ATPase from B, but these levels were similarly preserved at 4 and 30 degrees C. HSP70-1 levels were mildly elevated (fourfold) above B to similar levels at all three temperatures. These results indicate that mRNA expression for ANT1 and beta F1-ATPase is specifically preserved in a pattern consistent with the temperature threshold phenomenon. HSP70-1 expression is not influenced by ischemic temperature. Preservation of gene expression for these mitochondrial proteins implies that signaling for mitochondrial biogenesis or resynthesis is maintained after ischemic insult.

Hypothermia preserves function and signaling for mitochondrial biogenesis during subsequent ischemia.

Hypothermia is known to protect myocardium during ischemia, but its role in induction of a protective stress response before ischemia has not been evaluated. As cold incites stress responses in other tissues, including heat shock protein induction and signaling mitochondrial biogenesis, we postulated that hypothermia in perfused hearts would produce similar phenomena while reducing injury during subsequent ischemia. Studies were performed in isolated perfused rabbit hearts (n = 77): a control group (C) and a hypothermic group (H) subjected to decreasing infusate temperature from 37 to 31 degrees C over 20 min. Subsequent ischemia during cardioplegic arrest at 34 degrees C for 120 min was followed by reperfusion. At 15 min of reperfusion, recovery of left ventricular developed pressure (LVDP), maximum first derivative of left ventricular pressure (LV dP/dtmax), LV -dP/dtmax, and the product of heart rate and LVDP was significantly increased in H (P < 0.01) compared with C hearts. Ischemic contracture started later in H (97.5 +/- 3.6 min) than in C (67.3 +/- 3.3 min) hearts. Myocardial ATP preservation and repletion during ischemia and reperfusion were higher in H than in C hearts. mRNA levels of the nuclear-encoded mitochondrial proteins adenine nucleotide translocase isoform 1 (ANT1) and beta-F1-adenosine-triphosphatase (beta-F1-ATPase) normalized to 28S RNA decreased in C hearts but were preserved in H hearts after reperfusion. Inducible heat shock protein (HSP70-1) mRNA was elevated nearly 4-fold after ischemia in C hearts and 12-fold in H hearts. These data indicate that hypothermia preserves myocardial function and ATP stores during subsequent ischemia and reperfusion. Signaling for mitochondrial biogenesis indexed by ANT1 and beta-F1-ATPase mRNA levels is also preserved during a marked increase in HSP70-1 mRNA.

Temperature threshold and modulation of energy metabolism in the cardioplegic arrested rabbit heart.

Hypothermia protects ischemic tissues by reducing ATP utilization and accumulation of harmful metabolites. However, it also reduces ATP production, which might cause deterioration in the energy supply/demand ratio. Modulation of energy supply/demand according to temperature has not been previously studied in detail. In this study, isolated, perfused rabbit hearts (n = 60) were used to determine the effects of various temperatures on myocardial energy metabolism and function during cardioplegic arrest. Ischemia was induced by crystalloid cardioplegic solution at 4, 18, 30, and 34 degrees C for 120 min, respectively. At each temperature, the hearts were divided into a glucose-treated group which contained 22 mM glucose in cardioplegic solution as the only substrate and a control group which contained 22 mM mannitol to keep same osmolarity. Following 15 min reperfusion, recovery of left ventricular developed pressure (DP), +/- dP/dtmax, and the product of heart rate and DP were significantly higher in 30, 18, and 4 degrees C groups than those in 34 degrees C control group. The functional recovery was also significantly higher in the 34 degrees C glucose-treated group than that in the 34 degrees C control group, but there was no difference between those groups at 30 degrees C and the temperature below 30 degrees C. Myocardial ATP concentration was significantly lower in 34 degrees C control group than those in other groups. There is a close relationship between myocardial ATP concentration and functional recovery (R2 = 0.90). The accumulations of lactate and CO2 were significantly higher at 34 degrees C in glucose-treated group than those in the control group. However, there was no significant difference between these two groups at 30 degrees C and the temperature below 30 degrees C. These results indicate that under these study conditions: (1) a marked decrease in energy supply/demand occurs above 30 degrees C, implying that a temperature threshold exists; and (2) this can be ameliorated by provision of glucose as substrate in cardioplegia solution.

Expression of adenine nucleotide translocator parallels maturation of respiratory control in heart in vivo.

Changes in the relationship between myocardial high-energy phosphates and oxygen consumption in vivo occur during development, implying that the mode of respiratory control undergoes maturation. We hypothesized that these maturational changes in sheep heart are paralleled by alterations in the adenine nucleotide translocator (ANT), which are in turn related to changes in the expression of this gene. Increases in myocardial oxygen consumption (MVO2) were induced by epinephrine infusion in newborn (0-32 h, n = 6) and mature sheep (30-32 days, n = 6), and high-energy phosphates were monitored with 31P nuclear magnetic resonance. Western blot analyses for the ANT1 and the beta-subunit of F1-adenosinetriphosphatase (ATPase) were performed in these hearts and additional (n = 9 total per group) as well as in fetal hearts (130-132 days of gestation, n = 5). Northern blot analyses were performed to assess for changes in steady-state RNA transcripts for these two genes. Kinetic analyses for the 31P spectra data revealed that the ADP-MVO2 relationship for the newborns conformed to a Michaelis-Menten model but that the mature data did not conform to first- or second-order kinetic control of respiration through ANT. Maturation from fetal to mature was accompanied by a 2.5-fold increase in ANT protein (by Western blot), with no detectable change in beta-F1-ATPase. Northern blot data show that steady-state mRNA levels for ANT and beta-F1-ATPase increased approximately 2.5-fold from fetal to mature. These data indicate that 1) respiratory control pattern in the newborn is consistent with a kinetic type regulation through ANT, 2) maturational decreases in control through ANT are paralleled by specific increases in ANT content, and 3) regulation of these changes in ANT may be related to increases in steady-state transcript levels for its gene.

Influence of the pH of cardioplegic solutions on cellular energy metabolism and hydrogen ion flux during neonatal hypothermic circulatory arrest and reperfusion: a dynamic 31P nuclear magnetic resonance study in a pig model.

OBJECTIVES: The pH of cardioplegic solutions is postulated to affect myocardial protection during neonatal hypothermic circulatory arrest. Neither optimization of cardioplegic pH nor its influence on intracellular pH during hypothermic circulatory arrest has been previously studied in vivo. Thus we examined the effects of the pH of cardioplegic solutions on postischemic cardiac function in vivo, including two possible operative mechanisms: (1) reduction in adenosine triphosphate use and depletion of high-energy phosphate stores or (2) reduction of H+ flux during reperfusion, or both. METHODS: Dynamic 31P spectroscopy was used to measure rates of adenosine triphosphate use, high-energy phosphate depletion, cytosolic acidification during hypothermic circulatory arrest, and phosphocreatine repletion and realkalinization during reperfusion. Neonatal pigs in three groups (n = 8 each)--group A, acidic cardioplegia (pH = 6.8); group B, basic cardioplegia (pH = 7.8); and group N, no cardioplegia--underwent hypothermia at 20 degrees C with 60 minutes of hypothermic cardioplegia followed by reperfusion. RESULTS: Recoveries of peak elastance, stroke work, and diastolic stiffness were superior in group B. Indices of ischemic adenosine triphosphate use, initial phosphocreatine depletion rate, and tau, the exponential decay half-time, were not different among groups. Peak [H+] in group A (end-ischemia) was significantly elevated over that of group B. The realkalinization rate was reduced in group B compared with that in groups A (p = 0.015) and N (p = 0.035), with no difference between groups A and N (p = 0.3). Cytosolic realkalinization rate was markedly reduced and the half-time of [H+] decay was increased during reperfusion in group B. CONCLUSIONS: Superior postischemic cardiac function in group B is not related to alterations in ischemic adenosine triphosphate use or high-energy store depletion, but may be due to slowing in H+ efflux during reperfusion, which should reduce Ca++ and Na+ influx.

Hypoxic pHi and function modulation by Na+/H+ exchange and alpha-adrenoreceptor inhibition in heart in vivo.

Regulation of intracellular pH (pHi) may contribute to maintenance of cardiac contractile function during graded hypoxia in vivo. To test this hypothesis, we disturbed pHi regulation in vivo using two approaches: alpha-adrenoreceptor antagonism with phentolamine (1 mg/kg) (Phen; n = 9); and Na+/H+ exchange inhibition with HOE-642 (2 mg/kg; n = 6) before graded hypoxia in open-chest sheep. Hemodynamic parameters including left ventricular maximal pressure development (dP/dtmax) cardiac index (CI), and left ventricular power were monitored continuously and simultaneously with high-energy phosphate levels and pHi, measured with 31P nuclear magnetic resonance spectroscopy in Phen, HOE-642, and control (Con; n = 9). In subgroups (n = 6) in Con and Phen, coronary flow, myocardial oxygen consumption (MVO2), and lactate uptake were also measured. During hypoxia, the functional parameters left ventricular dP/dtmax, CI, and left ventricular power decreased significantly compared with baseline and Con values. These decreases were preceded by a significant drop (P < 0.05) in pHi from 7.10 +/- 0.04 to 6.69 +/- 0.05 in Phen and corresponded temporally to a pHi drop from 7.10 +/- 0.02 to 6.77 +/- 0.03 in HOE-642. Decreases in pHi in Phen were not preceded by decreases in cardiac function or MVO2. In contrast, cardiac function parameters increased significantly in Con, whereas no significant pHi decrease occurred (7.07 +/- 0.03 to 6.98 +/- 0.04). We conclude that these data indicate that pHi regulation can be disrupted through alpha-adrenergic antagonism or Na+/H(+)-exchange inhibition in vivo. These studies demonstrate that pHi regulation performs a role in the modulation of cardiac function during hypoxia in vivo.