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Biomedical subjects

Yigal M Pinto

Publications and source records attributed to Yigal M Pinto.

11 recordsLinked to original sources
PubMed2003

Increased expression of cardiac angiotensin II type 1 (AT(1)) receptors decreases myocardial microvessel density after experimental myocardial infarction.

OBJECTIVE: To study the effects of increased levels of myocardial angiotensin II type 1 (AT(1)) receptor on microvascular growth following myocardial infarction (MI). METHODS: MI was created in transgenic rats (TGR) with a cardioselective overexpression of the AT(1) receptor. We used Sprague-Dawley (SD) rats as controls. Some of the rats were treated with the selective AT(1) receptor blocker losartan (Los). Rats were sacrificed after 3 weeks. RESULTS: MI caused left ventricular (LV) hypertrophy and LV dysfunction in both SD and TGR, which was prevented by AT(1) receptor blockade. Furthermore, MI decreased microvessel density in the non-infarcted myocardium (SD MI: 1653+/-37/mm(2), P<0.01 vs. sham-operated controls), however, microvessel density decreased significantly more in TGR with MI (1298+/-33/mm(2), P<0.01 vs. SD MI). AT(1) receptor blockade restored microvessel density (SD MI Los: 2046+/-195/mm(2); TGR MI Los: 1742+/-47/mm(2); P<0.01 vs. untreated). The differences in microvessel density were still present after correction for LV hypertrophy. The increase in microvessel density after AT(1) receptor blockade was not accompanied by increased myocardial vascular endothelial growth factor (VEGF) levels. Microvessel density correlated with parameters of myocardial stretch, such as LV end-diastolic pressure (-0.681, P<0.001) and N-ANP (-0.424, P=0.01). CONCLUSIONS: Microvessel density after MI is decreased when the AT(1) receptor is overexpressed, and this is amenable to AT(1) receptor blockade. This suggests that efficacy of AT(1) receptor blockers post-MI may not only be due to attenuation of LV remodeling, but also to a stimulatory effect on angiogenesis.

Angiotensin Receptor Antagonists↗
PubMed2003

Left ventricular hypertrophy: virtuous intentions, malign consequences.

Left ventricular hypertrophy (LVH) is currently the focus of intense cardiovascular research, with the resultant rapid evolution of novel concepts relating to its exceedingly complex pathophysiology. In addition to the alterations in signal transduction and disturbances in Ca(2+) homeostasis, there are structural changes in myofilaments, disorganization of the cytoskeletal framework and increased collagen synthesis. LVH is associated with progressive left ventricular remodeling that culminates to heart failure. The modern treatment of left ventricular hypertrophy is now largely based on the hypothesis that neuroendocrine activation is important in the progression of the disease and inhibition of neurohormones is likely to have long-term benefit with regard to morbidity and mortality. Drugs specifically designed to unload the left ventricle, such as diuretics and vasodilators, appears to be less effective in reducing LV mass and improving prognosis. Thus, the evolution of treatment for LVH itself has provided much enlightenment for our understanding of the fundamental biology of the disorder.

Activin Receptors, Type I↗
PubMed2003

Polymorphisms in the RAS and cardiac function.

Since the discovery of the polymorphism in the angiotensin converting enzyme (ACE) and the consequences of this polymorphism on the activity levels of the enzyme, numerous association studies have been performed. However, these investigations do not often adhere to the most stringent criteria for such studies. The initial study reporting a positive association of the ACE polymorphism and myocardial infarction showed an increased risk of the DD genotype. This initial association was eventually refuted by a large, well conducted association study, which found a risk ratio of 1.02 after combining their own data with all published data. Although such large, well conducted association studies have not been performed in left ventricular (LV) hypertrophy, the association between DD genotype and hypertrophy is more convincing with a 192% excess risk of LV hypertrophy in untreated hypertensives. The role of ACE genotype in LV growth is well established, especially in athletes. In heart failure, large studies or meta-analyses have not been performed, because most studies have selected different end-points. This hampers a proper meta-analysis of the results obtained in associations with heart failure. As most association studies do not fulfill the criteria for good association studies and use too small sample sizes, it remains important to perform a meta-analysis to add meaning to the results of such studies. Above all, it is important to obey the rules set for association studies, large sample size, small P values, report associations that make biological sense and alleles that affect the gene product in a physiologically meaningful way.

Heart Failure↗
PubMed2003

Endothelial dysfunction and infarct-size relate to impaired EDHF response in rat experimental chronic heart failure.

BACKGROUND: The rat coronary ligation model of chronic heart failure has been extensively used to investigate its pathophysiology including the role of endothelial dysfunction. Inconsistent results have been obtained concerning the role of endothelial dilative mediators nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). AIMS: Our aim was to investigate involvement of NO and EDHF in aortic endothelial dysfunction in this model and the influence of individual infarct sizes. Furthermore, we investigated whether it is justified to regard rats that failed to develop large infarct sizes as SHAM controls. METHODS: We performed coronary ligations and SHAM operations and studied acetylcholine (ACh)-induced relaxations and underlying endothelial mediators in isolated aortic rings 12 weeks after infarction. By then, cardiac and hemodynamic parameters were deteriorated in animals with large myocardial infarctions (large-MI, 35+/-3%), but not those with small myocardial infarctions (small-MI, 5+/-2%). RESULTS: Large-MI showed decreased ACh-induced relaxation compared to SHAM due to decreased contribution of EDHF which was inversely correlated with individual infarct-size. Interestingly, small-MI showed significantly increased ACh-induced relaxation compared to SHAM due to increased NO contribution. CONCLUSIONS: Our results suggest that impaired aortic endothelial dilatory function in large-MI is mainly due to an impaired EDHF response and strongly depends on individual infarct-size. In addition, endothelium-dependent relaxation of small-MI rats differed from SHAM, indicating that both groups may not be pooled to serve as controls. These results emphasize the importance of infarct-size and choice of the control group, and may explain inconsistencies in previous studies.

Acetylcholine↗
PubMed2003

The imbalance between oxygen demand and supply as a potential mechanism in the pathophysiology of heart failure: the role of microvascular growth and abnormalities.

In heart failure, a deficient oxygen supply often is a primary cause for myocardial dysfunction. The reverse however, may also be true; the changes that occur in the failing heart may predispose for the existence of tissue hypoxia, which further affects the function of the heart. Specifically, myocardial hypertrophy and accelerated heart rhythm enhance oxygen demand, while supply is hampered short by endothelial dysfunction and diffusion barriers (such as fibrosis, arterial hyperplasia, and myocyte hypertrophy). Another contributory factor may be deficient growth of the microvasculature that does not keep pace with the rate of myocardial hypertrophy. Fewer microvessels have been observed in many forms of cardiomyopathies. On the other hand, some distinct forms of cardiomyopathies are characterized by the compensatory growth of microvessels, or even excess angiogenesis. This review summarizes the knowledge that has been gathered on this topic thus far and discusses factors that mediate myocardial microvessel growth. Furthermore, a paradigm is presented in which the rate of microvessel growth predicts, at least in part, the degree of myocardial dysfunction. Therapies aimed at the restoration of the microcirculation are proposed to preserve and improve myocardial function.

Adaptation, Physiological↗
PubMed2002

Rapid bedside measurement of brain natriuretic peptide in patients with chronic heart failure.

BACKGROUND: Brain natriuretic peptide (BNP) levels have been used to assess clinical status and predict prognosis of patients with chronic heart failure (CHF). However, BNP levels can only be measured in specialized laboratories which has hampered its use in daily clinical practice. We compared a new, rapid, BNP assay with a conventional BNP measurement and evaluated the applicability to current practice by comparing it with standard clinical parameters. METHODS: BNP levels were determined in 78 stable CHF patients and 20 controls. The severity of CHF was assessed by determination of New York Heart Association functional class (NYHA), left ventricular ejection fraction (LVEF) and peak oxygen consumption (peak VO(2)), and these parameters were compared to BNP levels. RESULTS: Overall, rapid BNP assessment was highly correlated with the conventional BNP assay (r=0.95, P<0.0001). In the higher ranges (>200 pmol/l), however, correlation was less accurate, and tended to overestimate. BNP levels also strongly correlated with both NYHA class, LVEF and peak VO(2) (all P<0.001). A cut-off value for BNP of 20 pmol/l yielded a sensitivity of 91% and a specificity of 92% to detect the presence of left ventricular systolic dysfunction. CONCLUSIONS: Rapid measurement of BNP levels is comparable to conventional BNP measurement and strongly correlated to clinical tests that are currently used to stratify CHF patients. Wider use of this method may yield a reduction of costly and time-consuming clinical tests and may reduce the medical burden of CHF.

Adult↗
PubMed2002

Impaired coronary endothelial function in a rat model of spontaneous albuminuria.

BACKGROUND: Albuminuria is an independent risk factor of coronary artery disease and has been proposed to reflect a general endothelial disorder. The Munich Wistar Frömter (MWF) rat strain develops spontaneous albuminuria and, therefore, may be an interesting experimental model to study alterations of endothelial function under conditions of increased albuminuria. Our aim was to investigate if the MWF strain shows generalized endothelial dysfunction or endothelial dysfunction localized to the coronary vascular bed, and if so, determine which endothelial dilative mediators are involved. METHODS: Coronary and mesenteric arteries were investigated for endothelium-dependent relaxation and the contribution of prostacyclin, nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) in MWF rats compared to normal Wistar rats. In addition, as MWF rats show increased blood pressure, spontaneously hypertensive rats (SHR) with similar hypertension but without increased albuminuria also were studied. RESULTS: Maximal total endothelium-dependent relaxation of coronary arteries was strongly impaired in MWF rats (55 +/- 3%) compared to Wistar (89 +/- 5%) and SHR (89 +/- 2%) P < 0.05, respectively. The NO-mediated relaxation as well as the relaxation mediated by EDH were significantly lower in coronary arteries from MWF compared to Wistar. In mesenteric arteries of MWF the endothelium-dependent relaxation was intact. CONCLUSIONS: The strong impairment of coronary endothelium-dependent relaxation in the MWF model of spontaneous albuminuria may be due to defects in production or activity of NO and EDH. The intact mesenteric endothelium-dependent relaxation suggests that increased albuminuria may not be related to generalized endothelial vasodilator dysfunction in this model. Selective impairment of coronary endothelial function in a setting of spontaneous albuminuria may be a feature of the MWF that may be employed to further study cause-effect relations between albuminuria and coronary artery disease.

Albuminuria↗
PubMed2002

Inhibition of left ventricular fibrosis by tranilast in rats with renovascular hypertension.

BACKGROUND: Growth factors such as transforming growth factor-beta (TGF beta) are believed to have an essential role in cardiac fibrosis. Tranilast (N(3,4-dimethoxycinnamoyl) anthranilic acid) attenuates the increased expression of TGF beta mRNA in vitro. OBJECTIVE: To investigate whether tranilast reduces cardiac fibrosis in rats with two-kidney, one-clip (2K1C) renovascular hypertension. In addition, we tested the in-vitro effects of tranilast on cardiac myocytes and non-myocyte cells. METHODS: We analysed hearts from four groups of rats: sham-operated controls; rats with 2K1C renovascular hypertension; rats with 2K1C renovascular hypertension treated for 12 weeks with the angiotensin converting enzyme (ACE) inhibitor, quinapril (6 mg/kg per day); rats with 2K1C renovascular hypertension treated for 12 weeks with tranilast (400 mg/kg per day). RESULTS: Systolic blood pressure was reduced after quinapril treatment. Tranilast did not alter blood pressure (2K1C: 223 +/- 19 mmHg; 2K1C + quinapril: 149 +/- 15 mmHg (P < 0.01 compared with 2K1C); 2K1C + tranilast: 204 +/- 32 mmHg). Left ventricular weight was likewise reduced significantly by quinapril, but not significantly by tranilast (2K1C: 1.52 +/- 0.2 g; 2K1C + quinapril: 1.26 +/- 0.18 g (P < 0.05 compared with 2K1C); 2K1C + tranilast: 1.37 +/- 0.27 g). Using a computer-aided image analysis system, we demonstrated that tranilast prevented cardiac fibrosis in a blood-pressure-independent manner (P < 0.01 compared with 2K1C). Determination of the cardiac hydroxyproline content similarly revealed a significant reduction in cardiac fibrosis by tranilast (2K1C: 4.92 +/- 0.48 mg/mg; 2K1C + tranilast: 3.97 +/- 0.46 mg/mg; P < 0.05). The effect of tranilast on cardiac fibrosis was comparable to the effects of a blood-pressure-decreasing dose of the ACE inhibitor, quinapril. Cell culture experiments revealed that tranilast significantly decreased the proliferation of cardiac non-myocyte cells. Proliferation of cardiac myocytes was not altered. CONCLUSION: This study revealed that long-term treatment with tranilast markedly attenuated left ventricular fibrosis in rats with renovascular hypertension. This was most probably the result of an antiproliferative effect of tranilast on cardiac non-myocyte cells. Tranilast thus offers a unique new therapeutic approach to the reduction of TGF beta-mediated cardiac fibrosis in vivo.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2002

Efficacy of angiotensin II type 1 receptor blockade on reperfusion-induced arrhythmias and mortality early after myocardial infarction is increased in transgenic rats with cardiac angiotensin II type 1 overexpression.

Angiotensin II induces ischemia/reperfusion (I/R)-induced arrhythmias and blockade of the angiotensin II type 1 receptor (AT1R) may therefore be beneficial in preventing arrhythmias and decreasing mortality after myocardial infarction (MI). Because the AT1R is upregulated after myocardial ischemia, it was hypothesized that the level of AT1R expression would mediate the response to AT1R blockade. Transgenic (TGR) rats that overexpress the human AT1R and Sprague-Dawley rats were used as controls. Total duration of arrhythmia (seconds) after I/R injury was similar in TGR and SD rats (433 +/- 109 vs. 376 +/- 117, p = n.s.). AT1R blockade with losartan decreased total duration of arrhythmia in the TGR rats (433 +/- 110 s-164 +/- 48 s; p < 0.05), whereas it caused a nonsignificant increase in the SD rats (376 +/- 117 s-497 +/- 97). In vivo, survival in the first 24 hours after MI was impaired in TGR rats (39%; SD, 63%). Losartan improved survival significantly in TGR rats (from 39% to 80%, p < 0.05). A smaller, nonsignificant effect was observed in SD rats (63% to 81%). AT1R blockade is beneficial only when the AT1R was overexpressed, both in reducing the reperfusion-induced arrhythmias and mortality early after MI.

Angiotensin Receptor Antagonists↗
PubMed2002

N-acetyl-Ser-Asp-Lys-Pro inhibits phosphorylation of Smad2 in cardiac fibroblasts.

N-Acetyl-Ser-Asp-Lys-Pro (AcSDKP) is a specific substrate for the N-terminal site of ACE and increases 5-fold during ACE inhibitor therapy. It is known to inhibit the proliferation of hematopoietic stem cells and has also recently been reported to inhibit the growth of cardiac fibroblasts. We investigated its mode of action in cardiac fibroblasts by assessing its influence on transforming growth factor beta(1) (TGFbeta1)-mediated Smad signaling. AcSDKP inhibited the proliferation of isolated cardiac fibroblasts (P<0.05) but significantly stimulated the proliferation of vascular smooth muscle cells. Flow cytometry of rat cardiac fibroblasts treated with AcSDKP showed significant inhibition of the progression of cells from G0/G1 phase to S phase of the cell cycle. In cardiac fibroblasts transfected with a Smad-sensitive luciferase reporter construct, AcSDKP decreased luciferase activity by 55+/-9.7% (P=0.01). Moreover, phosphorylation and nuclear translocation of Smad2 was decreased in cardiac fibroblasts treated with AcSDKP. To conclude, AcSDKP inhibits the growth of cardiac fibroblasts and also inhibits TGFbeta1-stimulated phosphorylation of Smad2. Because AcSDKP increases substantially during ACE inhibitor therapy, this suggests a novel pathway independent of angiotensin II, by which ACE inhibitors can inhibit cardiac fibrosis.

Animals↗