Search PubMed⌕ Search

Biomedical subjects

Ajay M Shah

Publications and source records attributed to Ajay M Shah.

At least 37 records · Page 2Linked to original sources
PubMed2005

Regulation of cardiac contractile function by troponin I phosphorylation.

Cardiac troponin I (cTnI) is a key regulatory protein in cardiac muscle contraction and relaxation, linking Ca(2+)-troponin C binding with activation of crossbridge reactions with the thin filament. In recent years, it has become increasingly apparent that myofilament properties as well as changes in intracellular Ca(2+) have a major role in the dynamic modulation of contractile function. The phosphorylation of specific serine and threonine residues on cTnI by several different kinases represents a major physiological mechanism for alteration of myofilament properties. Furthermore, altered thin filament function plays an important role in the contractile dysfunction associated with heart failure. Modification of cTnI by protein kinases A and C has been extensively studied with especially useful information deriving from (a) in vitro studies in reconstituted detergent-skinned fibre bundles in which endogenous cTnI was replaced with various targeted cTnI mutants and (b) transgenic animals in which endogenous cTnI was similarly manipulated through overexpression of cardiomyocyte-targeted cTnI mutants. cTnI may also be specifically modified by protein kinase G, p21-activated kinases and by dephosphorylation. This review focuses on recent advances in understanding the mechanisms of cTnI modification by these kinases and the consequent functional effects both under physiological conditions and in pathophysiological settings.

Actin Cytoskeleton↗
PubMed2005

NADPH oxidase and endothelial cell function.

Intracellular ROS (reactive oxygen species) such as superoxide and H2O2 have been increasingly appreciated to have a role in endothelial pathophysiology. Of the several sources within the vasculature, a family of multi-subunit NADPH oxidases appears to be a predominant contributor of endothelial superoxide. More importantly, this enzyme system is activated by numerous stimuli and is involved in triggering diverse intracellular signalling pathways ('redox-sensitive' signalling pathways) that have a central role in conditions such as endothelial activation and inflammation, cell growth, apoptosis and hypertrophy. Furthermore, NADPH oxidase-derived superoxide contributes to the impairment of endothelium-dependent vasodilatation by inactivating nitric oxide; the resultant endothelial dysfunction is implicated in the pathophysiology of diseases such as atherosclerosis, hypertension, diabetic vasculopathy and heart failure. A detailed understanding of the regulation of NADPH oxidases and their modulation and downstream effects may define novel therapeutic targets for cardiovascular disease prevention and treatment in the clinical setting, in contrast with global antioxidant therapy which has to date been disappointing.

Cardiovascular Diseases↗
PubMed2005

GATA factors lie upstream of Nkx 2.5 in the transcriptional regulatory cascade that effects cardiogenesis.

Members of the GATA-4, -5, and -6 subfamily of transcription factors are co-expressed with the homeoprotein Nkx 2.5 in the precardiac mesoderm during the earliest stages of its specification and are known to be important determinants of cardiac gene expression. Ample evidence suggests that GATA factors and Nkx 2.5 cross-regulate each other's expression; however, the temporal order of the expression of these transcription factors in vivo remains unresolved, and thus precise definition of the role of the products of the genes they transcribe in early development has been difficult to assess. We employed P19 CL6 mouse embryonic carcinoma cells as a model to investigate this problem, because these cells, like embryonic stem cells, can be induced to differentiate along multiple lineages. Here we demonstrate that when P19 CL6 cells are induced to differentiate to a cardiogenic lineage, the expression of GATA-4 and GATA-6 is up-regulated prior to the transcriptional activation of Nkx 2.5. Moreover, over-expression of GATA-4 or -6 at the time of Nkx 2.5 induction results in a significant up-regulation of endogenous Nkx 2.5 transcription. Finally, it is known that a Nkx-dependent enhancer is necessary for GATA-6 expression within cardiomyocytes of the developing mouse embryo. We demonstrate that within undifferentiated P19 CL6 cells, GATA-6 expression is subject to active repression by a novel upstream element that possesses binding sites for factors involved in transcriptional repression that are conserved between mammalian species.

Animals↗
PubMed2005

Acute tumor necrosis factor alpha signaling via NADPH oxidase in microvascular endothelial cells: role of p47phox phosphorylation and binding to TRAF4.

Tumor necrosis factor alpha (TNF-alpha) receptor-associated factors (TRAFs) play important roles in TNF-alpha signaling by interacting with downstream signaling molecules, e.g., mitogen-activated protein kinases (MAPKs). However, TNF-alpha also signals through reactive oxygen species (ROS)-dependent pathways. The interrelationship between these pathways is unclear; however, a recent study suggested that TRAF4 could bind to the NADPH oxidase subunit p47phox. Here, we investigated the potential interaction between p47phox phosphorylation and TRAF4 binding and their relative roles in acute TNF-alpha signaling. Exposure of human microvascular endothelial cells (HMEC-1) to TNF-alpha (100 U/ml; 1 to 60 min) induced rapid (within 5 min) p47phox phosphorylation. This was paralleled by a 2.7- +/- 0.5-fold increase in p47phox-TRAF4 association, membrane translocation of p47phox-TRAF4, a 2.3- +/- 0.4-fold increase in p47phox-p22phox complex formation, and a 3.2- +/- 0.2-fold increase in NADPH-dependent O2- production (all P < 0.05). TRAF4-p47phox binding was accompanied by a progressive increase in extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38(MAPK) activation, which was inhibited by an O2- scavenger, tiron. TRAF4 predominantly bound the phosphorylated form of p47phox, in a protein kinase C-dependent process. Knockdown of TRAF4 expression using siRNA had no effect on p47phox phosphorylation or binding to p22phox but inhibited TNF-alpha-induced ERK1/2 activation. In coronary microvascular EC from p47phox-/- mice, TNF-alpha-induced NADPH oxidase activation, ERK1/2 activation, and cell surface intercellular adhesion molecule 1 (ICAM-1) expression were all inhibited. Thus, both p47phox phosphorylation and TRAF4 are required for acute TNF-alpha signaling. The increased binding between p47phox and TRAF4 that occurs after p47phox phosphorylation could serve to spatially confine ROS generation from NADPH oxidase and subsequent MAPK activation and cell surface ICAM-1 expression in EC.

Animals↗
PubMed2005

Endothelial function and weight loss in obese humans.

BACKGROUND: Obesity is a major risk factor for the development of endothelial dysfunction. We explored the effect of different degrees of body mass on endothelial function, lipids, systemic inflammation and glucose homeostasis and the effect of surgically-induced weight loss on endothelial function in severely obese humans. METHODS: A cross-sectional study of healthy subjects across a wide range of body fatness was performed to characterize the effect of obesity on flow-mediated dilatation (FMD), systemic inflammation, blood pressure and insulin sensitivity. A longitudinal study was performed to assess the effect of bariatric surgery induced weight loss on these parameters. 73 healthy subjects across a wide range of body mass were recruited; of these, 8 underwent bariatric surgery (median BMI 52.2 kg/m2, interquartile range 50.355.9). Endothelial dependent vasodilatation was measured using the brachial artery vasodilatory response to forearm hyperemia assessed using highresolution ultrasonography. RESULTS: Obese subjects were characterised by a complex collection of abnormalities, with hypertension, impaired glucose homeostasis, systemic inflammation and reduced FMD. BMI < or =25 kg/m2 (median FMD 9.7%, interquartile range 6.8-12.2), BMI >30 kg/m2 (median FMD 6.7% 4.8-7.5), P=0.01 comparing FMD in lean and obese subjects. A mean reduction in weight of 23.4 (4.6) kg produced an improvement in FMD from 5.3% (3.87.0) to 10.2% (7.6-13.3), P=0.01. CONCLUSIONS: Even moderate obesity leads to endothelial dysfunction. In severely obese subjects, FMD is normalized by weight loss. This improvement in FMD is associated with a decline in inflammatory markers, blood pressure and insulin. The improvement in FMD occurred despite patients remaining significantly obese. These results suggest that an integrated approach to improving endothelial function in obese humans may be necessary.

Adult↗
PubMed2005

Inducible nitric oxide synthase has divergent effects on vascular and metabolic function in obesity.

Previous studies have suggested an involvement of inducible nitric oxide synthase (iNOS) in obesity, but the relation, if any, between this and mechanisms underlying endothelial dysfunction in obesity is unknown. We studied mice fed an obesogenic high-fat or standard diet for up to 8 weeks. Obesity was associated with elevated blood pressure; resistance to the glucoregulatory actions of insulin; resistance to the vascular actions of insulin, assessed as the reduction in phenylephrine constrictor response of aortic rings after insulin preincubation (lean -21.7 +/- 11.5 vs. obese 18.2 +/- 15.5%; P < 0.05); and evidence of reactive oxygen species (ROS)-dependent vasodilatation in response to acetylcholine in aortic rings (change in maximal relaxation to acetylcholine after exposure to catalase: lean -2.1 +/- 6.0 vs. obese -15.0 +/- 3.8%; P = 0.04). Obese mice had increased expression of iNOS in aorta, with evidence of increased vascular NO production, assessed as the increase in maximal constriction to phenylephrine after iNOS inhibition with 1400W (lean -3.5 +/- 9.1 vs. obese 42.1 +/- 11.2%; P < 0.001). To further address the role of iNOS in obesity-induced vascular and metabolic dysfunction, we studied the effect of a high-fat diet in iNOS knockout mice (iNOS KO). Obese iNOS KO mice were protected against the development of resistance to insulin's glucoregulatory and vascular effects (insulin-dependent reduction in maximal phenylephrine response: obese wild-type 11.2 +/- 15.0 vs. obese iNOS KO -20.0 +/- 7.7%; P = 0.02). However, obese iNOS KO mice remained hypertensive (124.0 +/- 0.7 vs. 114.9 +/- 0.5 mmHg; P < 0.01) and had evidence of increased vascular ROS production. Although these data support iNOS as a target to protect against the adverse effects of obesity on glucoregulation and vascular insulin resistance, iNOS inhibition does not prevent the development of raised blood pressure or oxidative stress.

Acetylcholine↗
PubMed2004

Evidence for altered interleukin 18 (IL)-18 pathway in human heart failure.

Interleukin (IL)-18 is the interferon-gamma-inducing factor and has potent proinflammatory activities. IL-18 has been recently implicated in atherosclerotic plaque instability and myocardial ischemia-reperfusion injury. However, it is unknown whether IL-18 expression is increased in human myocardium or if it has any role in heart failure. We analyzed the expression of IL-18, its receptor IL-18Ralpha, and its endogenous inhibitor, IL-18 binding protein (IL-18BP) in myocardial tissue from patients with end-stage heart failure (ischemic or dilated cardiomyopathy) and controls by use of quantitative real-time reverse transcriptase polymerase chain reaction, Western blot or immunohistochemical techniques. Plasma levels of IL-18 were also determined in 48 patients with heart failure. IL-18 mRNA and protein levels were up-regulated in the myocardium of patients with ischemic cardiomyopathy. Both ischemic and dilated myocardium showed increased IL-18Ralpha levels, suggesting potential biological effects. In addition, mRNA levels of IL-18 BP were down-regulated in the failing myocardium. Finally, plasma IL-18 levels were significantly elevated in patients with heart failure and were higher in those who died at follow-up than in survivors. The results suggest a potential role for the immunoinflammatory IL-18 signaling pathway in the pathophysiology of heart failure and identify novel therapeutic targets for future testing.

Cardiac Output, Low↗
PubMed2004

NOX-2S is a new member of the NOX family of NADPH oxidases.

A novel isoform of the NOX-2 subunit of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase has been identified using expressed sequence tag (EST) database mining. The novel isoform, NOX-2S, is a splice variant of NOX-2 and includes a previously unidentified exon, mapped 6.4 kb downstream of exon III, and encodes an in-frame stop codon generating a predicted truncated protein of approximately 12.7 kDa, the smallest reported member of the NOX family. Thus, NOX-2S is predicted to have only two transmembrane domains, however, the new C-terminal sequence includes two new potential protein kinase C (PKC) phosphorylation sites. Expression of NOX-2S mRNA was detected in many mouse tissues, and several human cell lines including the myeloid cell line HL-60, and the B cell line Ramos, indicating that the splice variant is conserved in mouse and man. NOX-2S is found co-expressed together with NOX-2 in all of the tissues and cells under investigation, both nonphagocytic and phagocytic. Induction of the myeloid cell line HL-60 into the neutrophil phagocytic lineage by dimethyl sulphoxide (DMSO), led to a marked increase in NOX-2S and NOX-2 expression in the myelocyte rather than promyelocyte stages of differentiation. Furthermore, in the B-cell line Ramos, differentiated with the cytokine interferon-gamma (IFN-gamma), splicing was altered to increase NOX-2S mRNA generation over NOX-2. Here we have identified NOX-2S, the first reported normally occurring splice variant of NOX-2. The sequence identity between mouse and human NOX-2S strongly implies conservation in function and possibly a role for NOX-2S in the regulation of NADPH oxidase activity.

Alternative Splicing↗
PubMed2004

Analysis of ex vivo left ventricular pressure-volume relations in the isolated murine ejecting heart.

The development of microconductance technology to study cardiac pressure-volume relations in mice in vivo has significantly advanced the haemodynamic assessment of gene-modified models of cardiovascular disease. In this study, we describe the application of microconductance analysis of cardiac function to the isolated murine ejecting heart. This ex vivo model is complementary to the previously described in vivo preparation, allows assessment without confounding effects of anaesthetic or neurohumoral influences and enables careful control of cardiac loading (particularly preload). Ex vivo pressure-volume relations in the isolated murine heart are sensitive to changes in myocardial contractility induced by beta-adrenoceptor stimulation or beta-adrenoceptor blockade, as well as the effects of chronic pressure overload induced by aortic banding. We present data for both steady-state analyses of the Frank-Starling relation and for assessment of the left ventricular pressure-volume relation over variably loaded beats, which allows investigation of the end-systolic and end-diastolic pressure-volume relations. The measurement of ventricular volume in addition to pressure under carefully controlled loading conditions in the isolated ejecting heart allows a comprehensive analysis of cardiac contractile function, and provides a useful complementary model for the assessment of cardiac performance in murine models of heart disease.

Animals↗
PubMed2004

Increased neuronal nitric oxide synthase-derived NO production in the failing human heart.

Experimental data suggest that nitric oxide (NO) generated from neuronal NO synthase (nNOS) modulates the myocardial inotropic state. To assess the contribution of NO, derived from endothelial and neuronal isoforms, to the pathophysiology of congestive heart failure in human beings, we compared expression, localisation, and specific activity of NOS isoforms in myocardium from patients with dilated cardiomyopathy with those in controls who had died from head trauma or intracranial bleeds. Diseased hearts had a significant increase in nNOS mRNA and protein expression, and activity associated with the translocation of nNOS to the sarcolemma through interactions with caveolin 3. Enhanced nNOS activity counteracted a decrease in eNOS expression and activity. Our results provide evidence of increased nNOS-derived NO in the failing human heart. Such altered regulation may be important in the pathophysiology of cardiac dysfunction in human congestive heart failure.

Blotting, Western↗
PubMed2004

Opposing roles of p47phox in basal versus angiotensin II-stimulated alterations in vascular O2- production, vascular tone, and mitogen-activated protein kinase activation.

BACKGROUND: NADPH oxidase is a major source of vascular superoxide (O2-) production and is implicated in angiotensin II (Ang II)-induced oxidant stress. The p47phox subunit plays an important role in Ang II-induced oxidase activation, but its role in basal oxidase activity and vascular function is unclear. METHODS AND RESULTS: Aortae from p47phox-/- and matched wild-type (WT) mice (n=9/group) were incubated ex vivo with or without Ang II (200 nmol/L, 30 minutes) and then examined for (1) NADPH-dependent O2- production, (2) endothelium-dependent and -independent vascular relaxation, and (3) activation of mitogen-activated protein kinases (MAPKs). In the absence of Ang II, p47phox-/- vessels had slightly but significantly higher (1.3+/-0.1-fold; P<0.05) NADPH-dependent O2- production than WT; impaired relaxation to acetylcholine (maximum 54+/-4% versus 80+/-3%; P<0.05), which was normalized to WT levels by the O2- scavenger tiron or by Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride, and increased basal phosphorylation of ERK1/2, p38MAPK, and JNK compared with WT. In WT aortae, Ang II increased NADPH-dependent O2- production (2.5+/-0.5-fold; P<0.05), impaired relaxation to acetylcholine (maximum 60+/-6% versus 80+/-3%; P<0.05), and increased ERK1/2, p38MAPK, and JNK phosphorylation (P<0.05). In contrast, Ang II failed to increase O2- production, impair acetylcholine responses, or increase MAPK activation in p47phox-/- aortae. CONCLUSIONS: p47phox plays a complex dual role in the vasculature. It inhibits basal NADPH oxidase activity but is critical for Ang II-induced vascular dysfunction via activation of NADPH oxidase.

1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium ↗
PubMed2004

Essential role of troponin I in the positive inotropic response to isoprenaline in mouse hearts contracting auxotonically.

PKA-dependent phosphorylation of cardiac troponin I (cTnI) contributes significantly to beta-adrenergic agonist-induced acceleration of myocardial relaxation (lusitropy). However, the role of PKA-dependent cTnI phosphorylation in the positive inotropic response to beta-adrenergic stimulation is unclear. We studied the contractile response to isoprenaline (10 nm) in isolated hearts and isolated cardiomyocytes from transgenic mice with cardiac-specific expression of slow skeletal TnI (ssTnI, which lacks the N-terminal protein extension containing PKA-sensitive phosphorylation sites in cTnI) and matched wild-type littermate controls. As expected, the lusitropic effect of isoprenaline was significantly blunted in ssTnI hearts. However, the positive inotropic response to isoprenaline was also blunted in ssTnI hearts. This effect was especially prominent for ejection-phase indices in isolated auxotonically loaded ssTnI hearts whereas the positive inotropic response of isovolumic hearts or unloaded isolated myocytes was much less affected. Isoprenaline decreased left ventricular end-systolic volume in wild-type hearts (10.6 +/- 1.6 to 6.2 +/- 0.4 microl at a preload of 20 cmH(2)O; P < 0.05) but not transgenic hearts (11.4 +/- 1.3 to 10.9 +/- 1.3 microl; P= n.s.). Likewise, isoprenaline increased stroke work in control hearts (14.5 +/- 1.0 to 22.5 +/- 1.8 mmHg microl mg(-1); P < 0.05) but not transgenic hearts (15.4 +/- 1.3 to 18.3 +/- 1.2 mmHg microl mg(-1); P= n.s.). The end-systolic pressure-volume relation was increased by isoprenaline to a greater extent in control than transgenic hearts. However, isoprenaline induced a similar rise in intracellular Ca(2+) transients in transgenic and non-transgenic cardiomyocytes. These results indicate that cTnI has a pivotal role in the positive inotropic response of the murine heart to beta-adrenergic stimulation, an effect that is highly dependent on loading conditions and is most evident in the auxotonically loaded ejecting heart.

Animals↗
PubMed2004

Role of oxidative stress in cardiac remodelling after myocardial infarction.

Recovery from myocardial infarction is associated with a series of alterations in heart structure and function, collectively known as cardiac remodelling, which play a major role in the subsequent development of heart failure. Early remodelling involves infarct scar formation in the ischaemic zone whereas subsequent ventricular remodelling affects mainly the viable non-infarcted myocardium with especially profound alterations in the extracellular matrix. There is growing evidence for a role of oxidative stress and redox signalling in the processes underlying cardiac remodelling. Reactive oxygen species are a group of highly reactive molecules which have the potential to modulate several biological processes as well as cause tissue damage and dysfunction. Their effects can be beneficial or deleterious, depending on the concentrations produced, the site of production, and the overall redox status of the cell. Reactive oxygen species can be generated by all cardiovascular cell types. Under pathophysiological conditions, major enzymatic sources appear to be mitochondria, xanthine oxidase and the non-phagocytic NADPH oxidases. In this review, we outline the mechanisms underlying the progression of early and late cardiac remodelling with particular focus on the role of oxidative stress and the potential sources of reactive oxygen species which may be involved.

Journal Article↗
PubMed2004

Endothelial cell superoxide generation: regulation and relevance for cardiovascular pathophysiology.

The endothelial generation of reactive oxygen species (ROS) is important both physiologically and in the pathogenesis of many cardiovascular disorders. ROS generated by endothelial cells include superoxide (O2-*), hydrogen peroxide (H2O2), peroxynitrite (ONOO-*), nitric oxide (NO), and hydroxyl (*OH) radicals. The O2-* radical, the focus of the current review, may have several effects either directly or through the generation of other radicals, e.g., H2O2 and ONOO-*. These effects include 1) rapid inactivation of the potent signaling molecule and endothelium-derived relaxing factor NO, leading to endothelial dysfunction; 2) the mediation of signal transduction leading to altered gene transcription and protein and enzyme activities ("redox signaling"); and 3) oxidative damage. Multiple enzymes can generate O2-*, notably xanthine oxidase, uncoupled NO synthase, and mitochondria. Recent studies indicate that a major source of endothelial O2-* involved in redox signaling is a multicomponent phagocyte-type NADPH oxidase that is subject to specific regulation by stimuli such as oscillatory shear stress, hypoxia, angiotensin II, growth factors, cytokines, and hyperlipidemia. Depending on the level of oxidants generated and the relative balance between pro- and antioxidant pathways, ROS may be involved in cell growth, hypertrophy, apoptosis, endothelial activation, and adhesivity, for example, in diabetes, hypertension, atherosclerosis, heart failure, and ischemia-reperfusion. This article reviews our current knowledge regarding the sources of endothelial ROS generation, their regulation, their involvement in redox signaling, and the relevance of enhanced ROS generation and redox signaling to the pathophysiology of cardiovascular disorders where endothelial activation and dysfunction are implicated.

Animals↗
PubMed2004

Preserved glucoregulation but attenuation of the vascular actions of insulin in mice heterozygous for knockout of the insulin receptor.

Type 2 diabetes is preceded by years of insulin resistance and is characterized by reduced bioavailability of the antiatherosclerotic signaling molecule nitric oxide (NO) and premature atherosclerosis. The relationship between resistance to the glucoregulatory actions of insulin and its effects on the vasculature (in particular NO-dependent responses) is poorly characterized. We studied this relationship in mice heterozygous for knockout of the insulin receptor (IRKO), which have a mild perturbation of insulin signaling. Male heterozygous IRKO mice aged 8-12 weeks were compared with age- and sex-matched littermates. IRKO mice had fasting blood glucose, insulin, free fatty acid, and triglyceride levels similar to those of wild-type mice. Intraperitoneal glucose and insulin tolerance tests were also similar in the two groups. Insulin levels in response to a glucose load were approximately twofold higher in IRKO compared with wild-type mice (1.08 +/- 0.11 vs. 0.62 +/- 0.13 ng/ml; P = 0.004). Despite this mild metabolic phenotype, IRKO mice had increased systolic blood pressure (124 +/- 4 vs. 110 +/- 3 mmHg; P = 0.01). Basal NO bioactivity, assessed from the increase in tension of phenylephrine preconstricted aortic rings in response to the NO synthase inhibitor N(G)-monomethyl-l-arginine, was reduced in IRKO (61 +/- 14 vs. 152 +/- 30%; P = 0.005). Insulin-mediated NO release in aorta, assessed as the reduction in phenylephrine constrictor response after insulin preincubation, was lost in IRKO mice (5 +/- 8% change vs. 66 +/- 9% reduction in wild-type; P = 0.03). Insulin-stimulated aortic endothelial NO synthase phosphorylation was also significantly blunted in IRKO mice (P < 0.05). These data demonstrate that insulin-stimulated NO responses in the vasculature are exquisitely sensitive to changes in insulin-signaling pathways in contrast to the glucoregulatory actions of insulin. These findings underscore the importance of early intervention in insulin-resistant states, where glucose homeostasis may be normal but substantial abnormalities of the vascular effects of insulin may already be present.

Acetylcholine↗
PubMed2003

Contrasting roles of NADPH oxidase isoforms in pressure-overload versus angiotensin II-induced cardiac hypertrophy.

Increased production of reactive oxygen species (ROS) is implicated in the development of left ventricular hypertrophy (LVH). Phagocyte-type NADPH oxidases are major cardiovascular sources of ROS, and recent data indicate a pivotal role of a gp91phox-containing NADPH oxidase in angiotensin II (Ang II)-induced LVH. We investigated the role of this oxidase in pressure-overload LVH. gp91phox-/- mice and matched controls underwent chronic Ang II infusion or aortic constriction. Ang II-induced increases in NADPH oxidase activity, atrial natriuretic factor (ANF) expression, and cardiac mass were inhibited in gp91phox-/- mice, whereas aortic constriction-induced increases in cardiac mass and ANF expression were not inhibited. However, aortic constriction increased cardiac NADPH oxidase activity in both gp91phox-/- and wild-type mice. Myocardial expression of an alternative gp91phox isoform, Nox4, was upregulated after aortic constriction in gp91phox-/- mice. The antioxidant, N-acetyl-cysteine, inhibited pressure-overload-induced LVH in both gp91phox-/- and wild-type mice. These data suggest a differential response of the cardiac Nox isoforms, gp91phox and Nox4, to Ang II versus pressure overload.

Angiotensin II↗
PubMed2003

Cardiac dysfunction in the Goto-Kakizaki rat. A model of type II diabetes mellitus.

METHODS: Both isolated perfused hearts and isolated ventricular myocytes from GK and matched control Wistar rat hearts were studied. Percent myocyte twitch shortening (%TS) and corresponding intracellular calcium transients (indo-1 fluorescence ratio, R) were measured over a range of stimulation frequencies (0.5-2.5 Hz; 32 degrees C, n = 16-24 cells). In isolated Langendorff-perfused hearts, we measured systolic LV pressure (LVP(max)), left ventricular end diastolic pressure (LVEDP), maximal rate of LV pressure rise (LV dP/dt(max)) and fall (LV dP/dt(min)) and isovolumic LV relaxation (exponential time constant, T) both at baseline and during brief (10 minutes) hypoxia. RESULTS: The %TS and corresponding indo-1 R were similar between GK and control myocytes at all stimulation frequencies (e.g. at 2.5 Hz: % TS = 8.6 +/- 0.77 and 8.2 +/- 0.19; R = 0.19 +/- 0.009 and 0.18 +/- 0.018, GK and control respectively, P = NS). Similarly, there were no significant differences in baseline LVP(max) (129 +/- 6.2 and 135 +/- 9.6 mmHg; GK and control respectively, P = NS), LV dP/dt(max) (3169.5 +/- 165.80 and 3390.6 +/- 232.60 mmHg/s; GK and control respectively, P = NS), LV dP/dt(min) or T (24 +/- 0.7 and 25 +/- 0.6 ms, GK and control respectively, P = NS). During 10 min hypoxia, LV dP/dt(max) decreased significantly more, and LVEDP and T increased significantly more, in GK compared to control hearts (LV dP/dt(max): 668.90 +/- 32.8 versus 1027.10 +/- 84.0 mmHg/s; LVEDP: 21.4 +/- 4.3 versus 11.6 +/- 0.6 mmHg; T: 102 +/- 13.8 versus 56 +/- 3.0 ms; GK versus control respectively; all P < 0.05). These abnormalities in GK hearts were reversed with acute addition of insulin (0.01 i. u./ml) to the perfusion buffer. CONCLUSION: The GK model of Type II diabetes displays a mild cardiomyopathy evident as exaggerated diastolic dysfunction during hypoxia. The mechanism is likely to involve substrate deficiency. Experimental study of cardiac function in the diabetic heart has focussed mostly on models of Type I diabetes. We studied cardiac function in the Goto-Kakizaki (GK) rat, an inbred model of spontaneous non-obese, Type II diabetes.

Animals↗