The nitric oxide redox sibling nitroxyl partially circumvents impairment of platelet nitric oxide responsiveness.

Impaired platelet responsiveness to nitric oxide (NO resistance) is a common characteristic of many cardiovascular disease states and represents an independent risk factor for cardiac events and mortality. NO resistance reflects both scavenging of NO by superoxide (O2(-)), and impairment of the NO receptor, soluble guanylate cyclase (sGC). There is thus an urgent need for circumvention of NO resistance in order to improve clinical outcomes. Nitroxyl (HNO), like NO, produces vasodilator and anti-aggregatory effects, largely via sGC activation, but is not inactivated by O2(-). We tested the hypothesis that HNO circumvents NO resistance in human platelets. In 57 subjects with or without ischemic heart disease, platelet responses to the HNO donor isopropylamine NONOate (IPA/NO) and the NO donor sodium nitroprusside (SNP) were compared. While SNP (10µM) induced 29±3% (p<0.001) inhibition of platelet aggregation, IPA/NO (10µM) caused 75±4% inhibition (p<0.001). In NO-resistant subjects (n=28), the IPA/NO:SNP response ratio was markedly increased (p<0.01), consistent with partial circumvention of NO resistance. Similarly, cGMP accumulation in platelets was greater (p<0.001) with IPA/NO than with SNP stimulation. The NO scavenger carboxy-PTIO (CPTIO, 200µM) inhibited SNP and IPA/NO responses by 92±7% and 17±4% respectively (p<0.001 for differential inhibition), suggesting that effects of IPA/NO are only partially NO-mediated. ODQ (10µM) inhibited IPA/NO responses by 36±8% (p<0.001), consistent with a contribution of sGC/haem to IPA/NO inhibition of aggregation. There was no significant relationship between whole blood ROS content and IPA/NO responses. Thus the HNO donor IPA/NO substantially circumvents platelet NO resistance while acting, at least partially, as a haem-mediated sGC activator.

Enhanced phosphoinositide 3-kinase(p110α) activity prevents diabetes-induced cardiomyopathy and superoxide generation in a mouse model of diabetes.

AIMS/HYPOTHESIS: Diabetic cardiomyopathy is characterised by diastolic dysfunction, oxidative stress, fibrosis, apoptosis and pathological cardiomyocyte hypertrophy. Phosphoinositide 3-kinase (PI3K)(p110α) is a cardioprotective kinase, but its role in the diabetic heart is unknown. The aim of this study was to assess whether PI3K(p110α) plays a critical role in the induction of diabetic cardiomyopathy, and whether increasing PI3K(p110α) activity in the heart can prevent the development of cardiac dysfunction in a setting of diabetes. METHODS: Type 1 diabetes was induced with streptozotocin in adult male cardiac-specific transgenic mice with increased PI3K(p110α) activity (constitutively active PI3K [p110α], caPI3K] or decreased PI3K(p110α) activity (dominant-negative PI3K [p110α], dnPI3K) and non-transgenic (Ntg) mice for 12 weeks. Cardiac function, histological and molecular analyses were performed. RESULTS: Diabetic Ntg mice displayed diastolic dysfunction and increased cardiomyocyte size, expression of atrial and B-type natriuretic peptides (Anp, Bnp), fibrosis and apoptosis, as well as increased superoxide generation and increased protein kinase C ß2 (PKCß2), p22 ( phox ) and apoptosis signal-regulating kinase 1 (Ask1) expression. Diabetic dnPI3K mice displayed an exaggerated cardiomyopathy phenotype compared with diabetic Ntg mice. In contrast, diabetic caPI3K mice were protected against diastolic dysfunction, pathological cardiomyocyte hypertrophy, fibrosis and apoptosis. Protection in diabetic caPI3K mice was associated with attenuation of left ventricular superoxide generation, attenuated Anp, Bnp, PKCß2, Ask1 and p22 ( phox ) expression, and elevated AKT. Further, in cardiomyocyte-like cells, increased PI3K(p110α) activity suppressed high glucose-induced superoxide generation and enhanced mitochondrial function. CONCLUSIONS/INTERPRETATION: These results demonstrate that reduced PI3K activity accelerates the development of diabetic cardiomyopathy, and that enhanced PI3K(p110α) activity can prevent adverse cardiac remodelling and dysfunction in a setting of diabetes.

Coenzyme Q10 attenuates diastolic dysfunction, cardiomyocyte hypertrophy and cardiac fibrosis in the db/db mouse model of type 2 diabetes.

AIMS/HYPOTHESIS: An increase in the production of reactive oxygen species is commonly thought to contribute to the development of diabetic cardiomyopathy. This study aimed to assess whether administration of the antioxidant coenzyme Q(10) would protect the diabetic heart against dysfunction and remodelling, using the db/db mouse model of type 2 diabetes. Furthermore, we aimed to compare the efficacy of coenzyme Q(10) to that of the ACE inhibitor ramipril. METHODS: Six-week-old non-diabetic db/+ mice and diabetic db/db mice received either normal drinking water or water supplemented with coenzyme Q(10) for 10 weeks. Endpoint cardiac function was assessed by echocardiography and catheterisation. Ventricular tissue was collected for histology, gene expression and protein analysis. RESULTS: Untreated db/db diabetic mice exhibited hyperglycaemia, accompanied by diastolic dysfunction and adverse structural remodelling, including cardiomyocyte hypertrophy, myocardial fibrosis and increased apoptosis. Systemic lipid peroxidation and myocardial superoxide generation were also elevated in db/db mice. Coenzyme Q(10) and ramipril treatment reduced superoxide generation, ameliorated diastolic dysfunction and reduced cardiomyocyte hypertrophy and fibrosis in db/db mice. Phosphorylation of Akt, although depressed in untreated db/db mice, was restored with coenzyme Q(10) administration. We postulate that preservation of cardioprotective Akt signalling may be a mechanism by which coenzyme Q(10)-treated db/db mice are protected from pathological cardiac hypertrophy. CONCLUSIONS/INTERPRETATION: These data demonstrate that coenzyme Q(10) attenuates oxidative stress and left ventricular diastolic dysfunction and remodelling in the diabetic heart. Addition of coenzyme Q(10) to the current therapy used in diabetic patients with diastolic dysfunction warrants further investigation.

The endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) predicts LV mass independent of afterload.

BACKGROUND: Nitric oxide (NO) is a modulator of left ventricular hypertrophy (LVH) and myocardial relaxation. The impact of NO availability on development of LVH has never been demonstrated in humans. We tested the hypotheses that elevation of asymmetric dimethylarginine (ADMA) concentrations (biochemical marker of decreased NO generation), and impairment of vascular responsiveness to NO donor GTN, would each predict the presence of LVH and associated LV diastolic dysfunction in a normal aging population. METHODS AND RESULTS: In 74 subjects aged 68±6 years, LV volumes and mass indexed to height(2.7) (LVMI) were calculated from cardiac MRI. Despite the absence of clinically-defined LVH, there was a relationship (r=0.29; p=0.01) between systolic BP and LVMI. Both elevation of ADMA levels to the highest quartile or impairment of GTN responsiveness (determined by applanation tonometry) to the lowest quartile were determinants of LVMI independent of systolic BP (p=0.01 and p=0.03, respectively). Filling pressure (E/E' ratio from echocardiography) was increased in patients with impaired vascular NO responsiveness (p<0.05) irrespective of LVMI. ADMA remained a significant determinant of LVMI on multivariate analysis. CONCLUSIONS: These data imply that NO bioavailability within the myocardium modulates earliest stages of LVH development and facilitates development of diastolic dysfunction at a given LV mass.

Myocardial oxidative stress contributes to transgenic ß2-adrenoceptor activation-induced cardiomyopathy and heart failure.

BACKGROUND AND PURPOSE: While maintaining cardiac performance, chronic ß-adrenoceptor activation eventually exacerbates the progression of cardiac remodelling and failure. We examined the adverse signalling pathways mediated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and reactive oxygen species (ROS) after chronic ß2-adrenoceptor activation. EXPERIMENTAL APPROACH: Mice with transgenic ß2-adrenoceptor overexpression (ß2-TG) and non-transgenic littermates were either untreated or treated with an antioxidant (N-acetylcysteine, NAC) or NADPH oxidase inhibitors (apocynin, diphenyliodonium). Levels of ROS, phosphorylated p38 mitogen-activated protein kinase (MAPK), pro-inflammatory cytokines and collagen content in the left ventricle (LV) and LV function were measured and compared. KEY RESULTS: ß2-TG mice showed increased ROS production, phosphorylation of p38 MAPK and heat shock protein 27 (HSP27), expression of pro-inflammatory cytokines and collagen, and progressive ventricular dysfunction. ß2-adrenoceptor stimulation similarly increased ROS production and phosphorylation of p38 MAPK and HSP27 in cultured cardiomyocytes. Treatment with apocynin, diphenyliodonium or NAC reduced phosphorylation of p38 MAPK and HSP27 in both cultured cardiomyocytes and the LV of ß2-TG mice. NAC treatment (500 mg·kg⁻¹ ·day⁻¹) for 2 weeks eliminated the up-regulated expression of pro-inflammatory cytokines and collagen in the LV of ß2-TG mice. Chronic NAC treatment to ß2-TG mice from 7 to 10 months of age largely prevented progression of ventricular dilatation, preserved contractile function (fractional shortening 37 ± 5% vs. 25 ± 3%, ejection fraction 52 ± 5% vs. 32 ± 4%, both P < 0.05), reduced cardiac fibrosis and suppressed matrix metalloproteinase activity. CONCLUSION AND IMPLICATIONS: ß2-adrenoceptor stimulation provoked NADPH oxidase-derived ROS production in the heart. Elevated ROS activated p38 MAPK and contributed significantly to cardiac inflammation, remodelling and failure.

Comparisons of calculations with PARTRAC and NOREC: transport of electrons in liquid water.

Monte Carlo computer models that simulate the detailed, event-by-event transport of electrons in liquid water are valuable for the interpretation and understanding of findings in radiation chemistry and radiation biology. Because of the paucity of experimental data, such efforts must rely on theoretical principles and considerable judgment in their development. Experimental verification of numerical input is possible to only a limited extent. Indirect support for model validity can be gained from a comparison of details between two independently developed computer codes as well as the observable results calculated with them. In this study, we compare the transport properties of electrons in liquid water using two such models, PARTRAC and NOREC. Both use interaction cross sections based on plane-wave Born approximations and a numerical parameterization of the complex dielectric response function for the liquid. The models are described and compared, and their similarities and differences are highlighted. Recent developments in the field are discussed and taken into account. The calculated stopping powers, W values, and slab penetration characteristics are in good agreement with one another and with other independent sources.

The antioxidant tempol inhibits cardiac hypertrophy in the insulin-resistant GLUT4-deficient mouse in vivo.

Reactive oxygen species such as superoxide are implicated in cardiac hypertrophy, but their contribution to the cardiac complications of insulin resistance is unresolved. We tested the hypothesis that the antioxidant tempol attenuates cardiac hypertrophy in insulin-resistant mice. Mice with cardiac GLUT4 deletion (GLUT4-knockout), superimposed on global GLUT4 suppression (GLUT4-knockdown) were administered tempol for 4 weeks. Age-matched GLUT4-knockdown littermates were used as controls (14 mice/group). GLUT4-knockout mice exhibited marked cardiac hypertrophy: heart to body weight ratio was increased 61+/-7% and expression of the hypertrophic genes beta-myosin heavy chain and B-type natriuretic peptide (BNP) were elevated 5.5+/-0.7- and 6.2+/-1.5-fold relative to control, respectively. Pro-fibrotic pro-collagen III expression was also higher (3.8+/-0.7-fold) in the GLUT4-knockout myocardium (all p<0.001). Both gp91(phox) and Nox1 subunits of NADPH oxidase were also upregulated, 4.9+/-1.2- and 9.3+/-2.8-fold (both p<0.01). Tempol treatment significantly attenuated all of these abnormalities in GLUT4-knockout mice. Heart to body weight ratio was decreased, as was fold expression of beta-myosin heavy chain (to 3.8+/-0.8), BNP (to 2.5+/-0.5), pro-collagen III (to 1.9+/-0.4), gp91(phox) (to 0.9+/-0.3) and Nox1 (to 2.3+/-0.1, all p<0.05 versus untreated GLUT4-knockout mice). In addition, tempol upregulated ventricular expression of both thioredoxin-2 (confirming an antioxidant action) and glycogen synthase kinase-3beta (GSK-3beta). Tempol did not elicit any other significant changes in control mice. Cardiac superoxide generation, however, was not altered by GLUT4-knockout or tempol. In conclusion, tempol treatment reduced morphological and molecular evidence of cardiac hypertrophy in the GLUT4-knockout insulin-resistant mouse in vivo, even at doses insufficient to lower cardiac superoxide. Parallel reductions in pro-collagen III and NADPH oxidase have important implications for our understanding of the molecular basis of cardiac hypertrophy in the setting of insulin resistance. Antioxidants may offer new alternatives in this disorder.

Endothelial dysfunction limits the antihypertrophic action of bradykinin in rat cardiomyocytes.

We have previously demonstrated that bradykinin blocks hypertrophy of isolated cardiomyocytes: this is dependent on the release of nitric oxide from endothelial cells. In the present study, we investigated the influence of endothelial dysfunction on the antihypertrophic action of bradykinin. Angiotensin II (1 microM) induced a 34 +/- 2% increase in [3H]phenylalanine incorporation (P<0.001), an in vitro marker of hypertrophy, in adult rat cardiomyocytes co-cultured with bovine aortic endothelial cells. This response was blocked by bradykinin (10 microM), but restored by the nitric oxide synthase inhibitor. N(omega)-monomethyl-L-arginine (100 microM). However, the antihypertrophic effect of bradykinin in co-culture was abolished by 24 h pretreatment of endothelial cells with high glucose (25 mM, to mimic hyperglycemia) and attenuated by hydrogen peroxide (100 microM, to mimic oxidative stress). Pretreatment with oxidized low-density lipoprotein (100 microg/ml for 24 h, to mimic hyperlipidemia) was without effect. The hypertrophic response to angiotensin II was not modified by endothelial cell pretreatment. Furthermore, the ability of bradykinin to elevate cGMP (a marker for nitric oxide) in cardiomyocytes co-cultured with endothelial cells was attenuated by pretreatment with either high glucose or hydrogen peroxide. In conclusion, loss of the cardioprotective action of bradykinin against angiotensin II-induced hypertrophy was associated with impaired nitric oxide release from dysfunctional endothelial cells.

The positive inotropic effects of milrinone but not of digoxin are attenuated at short cycle lengths.

The effects of inotropically active agents on the left ventricular force-interval relation are a potential determinant of their clinical utility and safety. However, little information is available concerning the effects of noncatecholamine positive inotropic agents on this relation. Therefore this study compared the short-term effects of digoxin and milrinone on resting hemodynamics, frequency potentiation (FP), and mechanical restitution (MR) in patients undergoing nonemergency cardiac catheterization. Both digoxin and milrinone produced similar increases in LV + dP/dt at rest (12.2 +/- 1.3%, p < 0.000001 and 11.4 +/- 3.2%, p < 0.01, respectively). The positive inotropic effects of digoxin were marginally attenuated during FP (by 8.5 +/- 4.2% and 4.6 +/- 2.9% at 10 and 60 s, respectively, both p = NS compared with baseline). Similarly, on MRC analysis, the parameter c (a measure of sensitivity of contractile performance to reductions in cycle length) increased by 3.6 +/- 3.7% (p = NS). Whereas the positive inotropic effects of milrinone were not significantly attenuated during FP, they were abolished and possibly reversed at short cycle lengths on MR curve construction (6.8 +/- 5.9% negative inotropic effect at 60% of resting cycle length; p = NS; p < 0.05 vs. resting cycle length). In conclusion, in patients with well-preserved left ventricular systolic function, the positive inotropic effects of milrinone but not of digoxin are markedly dependent on heart rate. These properties may influence both relative safety and efficacy of both agents.

Hyperglycaemia abolishes the antihypertrophic efficacy of bradykinin in rat ventricular myocytes.

1. Bradykinin inhibits hypertrophy of rat ventricular myocytes, but only in the presence of endothelial cells. 2. The influence of hyperglycaemia on the ability of bradykinin to prevent hypertrophy was investigated in adult rat ventricular myocytes cocultured with bovine aortic endothelial cells (BAEC). 3. In myocytes cocultured with normal BAEC, angiotensin II (AngII; 1 mumol/L) significantly increased [3H]-phenylalanine incorporation (an in vitro marker of hypertrophy) by 32 +/- 2%. This was abolished by bradykinin (10 mumol/L). 4. Pretreatment of BAEC with high glucose (25 mmol/L for 24 h) prior to coculture with myocytes reduced the antihypertrophic effect of bradykinin, but did not modulate the hypertrophic effect of AngII. 5. Pretreatment of BAEC with hyperglycaemia abolishes the antihypertrophic efficacy of bradykinin in rat ventricular myocytes cocultured with BAEC. This has implications for the action of angiotensin-converting enzyme inhibitors.

Lipocortin-1 preserves myocardial responsiveness to beta-adrenergic stimulation in rat papillary muscle.

1. During septic shock, myocardial contractile dysfunction is accompanied by the release of cytokines and enhanced production of nitric oxide, and the contractile dysfunction is prevented by glucocorticoids. 2. Myocardial dysfunction was induced in vitro by incubation of rat papillary muscle for 15 h with endotoxin (lipopolysaccharide, LPS) and interferon-gamma (IFN-gamma). 3. Both baseline contractile function and inotropic responsiveness to isoprenaline were markedly reduced by the combination of LPS plus IFN-gamma. 4. Lipocortin-1 (LC-1) is induced by glucocorticoids, and LC-1(2-26), its N-terminal fragment, protected the papillary muscle inotropic responsiveness to isoprenaline, but did not affect the decline in baseline contractile function induced by LPS plus IFN-gamma. 5. The mechanisms of this protective action need to be explored further, but LC-1 may prove to be a novel cardioprotective agent for the management of septic shock.

Bradykinin-stimulated protein synthesis by myocytes is dependent on the MAP kinase pathway and p70(S6K).

Bradykinin (BK) has a direct hypertrophic effect on rat ventricular cardiomyocytes (VCM) as defined by an increase in protein synthesis and an increase in atrial natriuretic peptide mRNA and secretion. In the current study, we have examined the dependence of BK-induced protein synthesis on activation of 90-kDa ribosomal S6 kinase (p90(rsk)) and 70-kDa S6 kinase (p70(S6K)). Both of these kinases possess the ability to phosphorylate the ribosomal protein S6, which plays an important role in initiating mRNA translation. Stimulation of adult VCM with 10 microM BK increased p90(rsk) activity by 2.5 +/- 0.3-fold and increased p70(S6K) activity by 2.0 +/- 0.3-fold. p90(rsk) is a terminal kinase in the mitogen-activated protein (MAP) kinase pathway. Inhibition of MAP kinase kinase activation by Raf in the MAP kinase pathway with PD-098059 (25 microM) blocked BK-stimulated activation of p90(rsk) by 70% and unexpectedly blocked p70(S6K) by 72%. Rapamycin inhibited BK-stimulated p70(S6K) activity by 93% but had no effect on p90(rsk) activation by BK. Inhibition of the MAP kinase pathway and p70(S6K) with PD-098059 was paralleled by changes in protein synthesis. BK (10 microM) increased [3H]phenylalanine incorporation by 27 +/- 3 and 39 +/- 6% in cultured adult and neonatal VCM, respectively. Treatment with PD-098059 or rapamycin abolished the increase in protein synthesis stimulated by BK. These results suggest that 1) BK activates p70(S6K) and p90(rsk); 2) although both p70(S6K) and p90(rsk) have the potential to phosphorylate the ribosomal S6 protein, p70(S6K) and not p90(rsk) is the predominant kinase involved in increasing protein synthesis by BK; and 3) p70(S6K) activation is dependent on stimulation of the MAP kinase pathway at a point distal to Raf.

Angiotensin II-induced hypertrophy of adult rat cardiomyocytes is blocked by nitric oxide.

The aim of the present study was to test the hypothesis that bradykinin-stimulated release of nitric oxide (NO) and/or prostacyclin from endothelium blocks myocyte hypertrophy in vitro. Angiotensin II increased [3H]phenylalanine incorporation by 21 +/- 2% in myocytes cocultured with endothelial cells; this was abolished by bradykinin in the presence of endothelial cells. Bradykinin increased cytosolic concentrations of cGMP by 29 +/- 4% in myocytes cocultured with endothelial cells. This was abolished by inhibition of NO synthase and by a cyclooxygenase inhibitor. Angiotensin II also increased [3H]phenylalanine incorporation by 28 +/- 3% in myocytes cultured in the absence of endothelial cells. This effect of angiotensin II in monoculture was abolished by donors of NO but not by bradykinin. Neither the stable analog of prostacyclin (iloprost) nor the prostacyclin second messanger analog 8-bromo-cAMP (8-BrcAMP) blocked the effect of angiotensin II. Furthermore, 8-BrcAMP and iloprost individually increased [3H]phenylalanine incorporation. The antihypertrophic effects of bradykinin are critically dependent on endothelium-derived NO.

Androgen receptors mediate hypertrophy in cardiac myocytes.

BACKGROUND: The role of androgens in producing cardiac hypertrophy by direct action on cardiac myocytes is uncertain. Accordingly, we tested the hypothesis that cardiac myocytes in adult men and women express an androgen receptor gene and that myocytes respond to androgens by a hypertrophic response. METHODS AND RESULTS: We used reverse transcription-polymerase chain reaction methods to demonstrate androgen receptor transcripts in multiple tissues and [3H]phenylalanine incorporation and atrial natriuretic peptide secretion as markers of hypertrophy in cultured rat myocytes. Messenger RNA encoding androgen receptors was detected in myocytes of male and female adult rats, neonatal rat myocytes, rat heart, dog heart, and infant and adult human heart. Both testosterone and dihydrotestosterone produced a robust receptor-specific hypertrophic response in myocytes, determined by indices of protein synthesis and atrial natriuretic peptide secretion. CONCLUSIONS: Androgen receptors are present in cardiac myocytes from multiple species, including normal men and women, in a context that permits androgens to modulate the cardiac phenotype and produce hypertrophy by direct, receptor-specific mechanisms. There are clinical implications for therapeutic or illicit use of androgens in humans.

Elimination, but not accumulation, of metoprolol by rat isolated perfused heart is selectively impaired by hypoxia.

1. The influence of hypoxia on the time course of regional myocardial accumulation and elimination of the beta 1-adrenoceptor antagonist metoprolol was investigated by a spontaneously beating rat isolated perfused heart preparation. 2. Myocardial metoprolol content was maximal at 2 min in the left and right ventricles and atria. Neither the extent nor the time of maximal myocardial metoprolol content was significantly influenced by the induction of hypoxia. However, maximal myocardial metoprolol content in both atria and right ventricles was significantly higher than that in the left ventricular samples (P < 0.02; one-factor analysis of variance, 17 d.f.). 3. Elimination of metoprolol (as indicated from residual myocardial metoprolol content at 10 min) was impaired in hypoxic left ventricles (P < 0.01 vs normoxia; unpaired t-test, 10 d.f.) but not in right ventricles or atria. This variation in myocardial metoprolol disposition was not apparent from examination of serial metoprolol concentrations in coronary perfusate. 4. Hypoxia selectively impaired the elimination of metoprolol from the left ventricle, but not the process of drug accumulation, by any region of myocardium. It remains to be determined whether this reflects regional variation in the extent of microcirculatory impairment associated with hypoxia.

Short-term myocardial uptake of d- and l-sotalol in humans: relation to hemodynamic and electrophysiologic effects.

The myocardial concentration of many cardioactive drugs has been identified as an important determinant of their short-term effects in previous studies. Although sotalol is frequently administered via short-term intravenous injection, no previous studies had sought to correlate its uptake by the heart with its various effects. We determined the time course of short-term uptake of d,l-sotalol by human myocardium in vivo and investigated the relation between myocardial content of sotalol and the short-term hemodynamic, electrocardiographic, and electrophysiologic effects of the drug. Sixteen patients received a 20-mg intravenous bolus of sotalol at the time of diagnostic cardiac catheterization. Myocardial content of d- and l-sotalol (by using a paired transcoronary sampling technique) and the short-term hemodynamic and electrophysiologic effects of the drug were determined < or = 20 min after injection. Myocardial accumulation of sotalol was not enantioselective, proceeded very rapidly (maximal at 0.74 +/- 0.10 min, representing 2.05 +/- 0.45% of the total injected dose), and was not significantly influenced by left ventricular systolic function or the extent of coronary artery disease. Approximately one third of peak myocardial content was still present 17.5 min after sotalol administration. Maximal effects of the drug (reduction in spontaneous heart rate, p < 0.005; reduction in maximal rate of LV pressure increase (LV+dP/dtmax, p < 0.005); and prolongation of PR intervals, p < 0.02) were delayed by approximately 10 min relative to maximal myocardial sotalol content. The significant prolongation of AH intervals (p < 0.01) and atrioventricular nodal effective refractory periods (p < 0.0002) that was observed was also maximal 10 min after administration of sotalol. Thus a consistent delay between myocardial sotalol content and the short-term effects of the drug was observed. In conclusion, the accumulation of both d- and l-sotalol by the human myocardium is more rapid than that of any other agent studied to date, with considerable hysteresis between myocardial drug uptake and subsequent cardiac effects.

Relationship between myocardial milrinone content and its acute hemodynamic and electrophysiologic effects.

One of the major determinants of the short-term effects of many cardioactive drugs is the concentration of the drug specifically within the myocardium. However, no information regarding the disposition of the phosphodiesterase inhibitor milrinone in the heart is available. We therefore determined the time course of short-term myocardial milrinone uptake from paired transcoronary sampling and simultaneous coronary sinus blood flow after a 1-mg intravenous bolus in patients undergoing diagnostic cardiac catheterization. In accordance with this intention, a sensitive, reproducible method for the determination of milrinone in human whole-blood samples was developed. The reverse-phase high-performance liquid chromatographic method described used a C18 column with UV-absorbance detection at 326 nm, with a limit of detection of 0.6 ng/ml, and was highly reproducible. The short-term hemodynamic and electrophysiologic effects of the drug also were determined. Significant increases in spontaneous heart rate and LV+dP/dtmax (at constant heart rate) were observed, accompanied by reductions in mean arterial pressure, systemic vascular resistance, and PR interval, without significant changes in atrioventricular nodal or ventricular effective refractory periods. Peak content (1.89 +/- 0.30% of injected dose) was rapidly attained, 0.56 +/- 0.06 min after milrinone injection. Time of peak effects was significantly delayed (7-10 min after injection) relative to time of peak myocardial milrinone content. Residual myocardial milrinone content was 69.1 +/- 5.7% of maximum 12.5 min after injection. It is concluded that both myocardial uptake and the onset of positive inotropic effects after intravenous injection of milrinone were very rapid. However, there was significant hysteresis between peak myocardial content and subsequent hemodynamic effects.

Myocardial effect compartment modeling of metoprolol and sotalol: importance of myocardial subsite drug concentration.

We have recently reported the time course of acute myocardial drug uptake and simultaneous pharmacodynamic effects for metoprolol (4 mg; n = 12) and sotalol (20 mg; n = 10) in patients with ischemic heart disease. The acute pharmacodynamic effects of the two drugs included reductions in both spontaneous heart rate and the contractile index peak positive rate of left ventricular pressure rise and prolongation of the electrocardiographic PR interval, all of which exhibited an equilibration delay compared with myocardial drug content. The objective of the current study was to analyze the relationship between myocardial drug content and effect for both metoprolol and sotalol using an effect compartment model, to examine the potential for the two drugs to share a common subsite of action in the myocardium. The time course of myocardial drug content was best described by a one-compartment model for metoprolol and a two-compartment model for sotalol. A linear pharmacodynamic model, relating the amount of drug at the effect-site (Ae) with each of the three effects, was used in the effect compartment modeling. The slope of each of these effects as a function of Ae was considerably flatter for sotalol than for metoprolol, reflecting the relative beta-adrenoceptor antagonistic potencies of the two drugs. The exit rate constant from the effect compartment (K(eo)) did not differ significantly from each other or from the exit rate constant from the "peripheral" compartment (K21) for sotalol. The results suggest that the effect compartment within the myocardium for both drugs may correspond to a "peripheral" compartment, even though a "peripheral" pharmacokinetic compartment for myocardial metoprolol content was not apparent. Thus, the effect compartment for many cardioactive drugs may correspond to a pharmacokinetically "peripheral" compartment, irrespective of localization of effect to a small (e.g. sinoatrial node) or large (e.g. ventricular myocardium) region of the heart.

Bradykinin blocks angiotensin II-induced hypertrophy in the presence of endothelial cells.

Angiotensin-converting enzyme inhibitors block left ventricular hypertrophy in vivo. A component of this effect has been attributed to tissue accumulation of bradykinin. Little is known regarding the effect of bradykinin on cardiomyocytes. The objectives of the present study were to define the effects of bradykinin on isolated ventricular cardiomyocytes (from adult and neonatal rat hearts) and to determine the extent to which bradykinin blocks hypertrophy in vitro. Bradykinin was found to be a hypertrophic agonist, as defined by increased protein synthesis and atrial natriuretic peptide secretion and expression. Bradykinin (10 micromol/L) increased [3H]phenylalanine incorporation by 23+/-3% in adult and by 36+/-10% in neonatal cardiomyocytes. Constitutive atrial natriuretic peptide secretion by neonatal myocytes was increased 357+/-103%. All effects of bradykinin were abolished by the B2-kinin receptor antagonist Hoe 140. These increases were similar in magnitude to those observed with phenylephrine (20 micromol/L) and angiotensin II (1 micromol/L). However, in cardiomyocytes cocultured with endothelial cells, bradykinin did not increase protein synthesis. Angiotensin II increased [3H]phenylalanine incorporation by 24+/-3% in adult cardiomyocytes in monoculture and by 22+/-2% in adult rat cardiomyocytes cocultured with endothelial cells. Bradykinin abolished this angiotensin II-induced hypertrophy in myocytes cultured with endothelial cells but not in myocytes studied in the absence of endothelial cells. In conclusion, bradykinin has a direct hypertrophic effect on ventricular myocytes. The presence of endothelial cells is required for the antihypertrophic effects of bradykinin. The results suggest that the increase in local concentration of bradykinin associated with angiotensin-converting enzyme inhibition is an important mechanism by which hypertrophy can be blocked. Manifestation of this mechanism appears to require bradykinin-stimulated release of paracrine factor(s) from endothelial cells, which are also able to block the hypertrophic effects of Ang II.

The force-interval relationship of the left ventricle: a quantitative description in patients with ischemic heart disease.

Quantitative descriptions of the mechanical restitution curve as a description of variability in ventricular performance with coupling interval in isolated tissue preparations are widely available. In humans, however, in vivo examination of the force-interval relationship is restricted to test pulse intervals shorter than the sinus cycle length (i.e., incomplete mechanical restitution). The primary objectives in this investigation were therefore to examine this aspect of mechanical restitution in patients with ischemic heart disease and to develop a quantitative description of the phenomenon. Mechanical restitution curves were constructed in 40 patients, most of whom had well-preserved left ventricular (LV) systolic function, undergoing diagnostic cardiac catheterization for the investigation of chest pain, using a single premature test pulse interval during baseline atrial pacing. The mechanical restitution curve, the relationship between LV + dP/dtmax and test pulse interval, was fitted to a rectangular hyperbolic function. From this, the parameter c, the calculated proportional decrease in LV + dP/dtmax at 60% of the resting cycle length, was derived. The mechanical restitution curve-fitting model (involving determination of c) satisfactorily described the force-interval relationship in 37 of the 40 patients studied (as a rectangular hyperbola in 31 and with simple linear regression in 6 patients). The refractory period of the atria/atrioventricular node limited accurate use of the model in the remaining three patients. The parameter c was inversely proportional to both baseline atrial pacing cycle length (P < .001) and LV ejection fraction (P < .02) In patients with normal LV ejection fractions, the derived value of c at a cycle length of 800 ms (c800) was 29.0% baseline LV + dP/dtmax (95% confidence interval, 23.0, 35.0). The presence of hemodynamically significant ischemic heart disease was not a predictor of the parameters of the model. After intravenous injection of the beta-adrenoreceptor antagonist metoprolol in seven patients, there was a significant (P < .05) reduction in both c and LV + dP/dtmax at the baseline atrial pacing cycle length. Thus, the force-interval relationship can be quantitatively studied using incomplete mechanical restitution curves in humans in vivo. This quantitative description probably reflects relative intracellular calcium availability via slow channel activity and can be used to assess effects of cardioactive drugs on frequency-dependent inotropic mechanisms in humans. The predictive value of this mechanical restitution curve model for hemodynamic instability during tachycardia in patients with impaired LV function remains to be determined.