Targeting the Main Anatomopathological Features in Animal Models of Myocardial Infarction.

Cardiovascular disease is the leading cause of human mortality and disability worldwide, primarily due to myocardial infarction (MI) and the resultant heart failure. To address this, animal models of MI have been developed to better understand the pathophysiological process and to enable the discovery and development of new therapies. The most commonly used small and large mammal models of MI accurately reproduce histopathologically the four characteristic post-MI phases: cardiac cell death, inflammation, myocardial repair and remodelling. However, differences between the time of onset of each characteristic phase and the kinetics of various cellular reactions between human MI and animal models, and between animal models, require careful consideration when defining the variables to be analysed and the timepoints of assessment in experimental studies. Typically, the progression of the different phases post-MI occur more rapidly in rodent models compared with large-animal models and man, suggesting the use of large-animal models is more translational for studying human MI. This review provides an overview of the main anatomopathological features of small and large animal models of MI and discusses the key species-specific histopathological similarities and differences.

Enhanced monocyte recruitment and delayed alternative macrophage polarization accompanies impaired repair following myocardial infarction in C57BL/6 compared to BALB/c mice.

Activation of the innate immune response following myocardial infarction (MI) is essential for infarct repair. Preclinical models of MI commonly use C57BL/6 mice, which have a type 1-dominant immune response, whereas other mouse strains such as BALB/c mice have a type 2-dominant immune response. We compared C57BL/6 and BALB/c mice to investigate whether predisposition towards a proinflammatory phenotype influences the dynamics of the innate immune response to MI and associated infarct healing and the risk of cardiac rupture. MI was induced by permanent coronary artery ligation in 12-15-week-old male wild-type BALB/c and C57BL/6 mice. Prior to MI, C57BL/6 mice had a lower proportion of CD206+ anti-inflammatory macrophages in the heart and an expanded blood pool of proinflammatory Ly6Chigh monocytes in comparison to BALB/c mice. The systemic inflammatory response in C57BL/6 mice following MI was more pronounced, with greater peripheral blood Ly6Chigh monocytosis, splenic Ly6Chigh monocyte mobilization and myeloid cell infiltration of pericardial adipose tissue. This led to an increased and prolonged macrophage accumulation, as well as delayed transition towards anti-inflammatory macrophage polarization in the infarct zone and surrounding tissues of C57BL/6 mice. These findings accompanied a higher rate of mortality due to cardiac rupture in C57BL/6 mice compared with BALB/c mice. We conclude that lower post-MI survival of C57BL/6 mice over BALB/c mice is mediated in part by a more pronounced and prolonged inflammatory response. Outcomes in BALB/c mice highlight the therapeutic potential of modulating resolution of the innate immune response following MI for the benefit of successful infarct healing.

Antenatal dexamethasone treatment transiently alters diastolic function in the mouse fetal heart.

Endogenous glucocorticoid action is important in the structural and functional maturation of the fetal heart. In fetal mice, although glucocorticoid concentrations are extremely low before E14.5, glucocorticoid receptor (GR) is expressed in the heart from E10.5. To investigate whether activation of cardiac GR prior to E14.5 induces precocious fetal heart maturation, we administered dexamethasone in the drinking water of pregnant dams from E12.5 to E15.5. To test the direct effects of glucocorticoids upon the cardiovascular system we used SMGRKO mice, with Sm22-Cre-mediated disruption of GR in cardiomyocytes and vascular smooth muscle. Contrary to expectations, echocardiography showed no advancement of functional maturation of the fetal heart. Moreover, litter size was decreased 2 days following cessation of antenatal glucocorticoid exposure, irrespective of fetal genotype. The myocardial performance index and E/A wave ratio, markers of fetal heart maturation, were not significantly affected by dexamethasone treatment in either genotype. Dexamethasone treatment transiently decreased the myocardial deceleration index (MDI; a marker of diastolic function), in control fetuses at E15.5, with recovery by E17.5, 2 days after cessation of treatment. MDI was lower in SMGRKO than in control fetuses and was unaffected by dexamethasone. The transient decrease in MDI was associated with repression of cardiac GR in control fetuses following dexamethasone treatment. Measurement of glucocorticoid levels in fetal tissue and hypothalamic corticotropin-releasing hormone (Crh) mRNA levels suggest complex and differential effects of dexamethasone treatment upon the hypothalamic-pituitary-adrenal axis between genotypes. These data suggest potentially detrimental and direct effects of antenatal glucocorticoid treatment upon fetal heart function.

Manganese-Enhanced T1 Mapping in the Myocardium of Normal and Infarcted Hearts.

Background: Manganese-enhanced MRI (MEMRI) has the potential to identify viable myocardium and quantify calcium influx and handling. Two distinct manganese contrast media have been developed for clinical application, mangafodipir and EVP1001-1, employing different strategies to mitigate against adverse effects resulting from calcium-channel agonism. Mangafodipir delivers manganese ions as a chelate, and EVP1001-1 coadministers calcium gluconate. Using myocardial T1 mapping, we aimed to explore chelated and nonchelated manganese contrast agents, their mechanism of myocardial uptake, and their application to infarcted hearts. Methods: T1 mapping was performed in healthy adult male Sprague-Dawley rats using a 7T MRI scanner before and after nonchelated (EVP1001-1 or MnCl2 (22 µmol/kg)) or chelated (mangafodipir (22-44 µmol/kg)) manganese-based contrast media in the presence of calcium channel blockade (diltiazem (100-200 µmol/kg/min)) or sodium chloride (0.9%). A second cohort of rats underwent surgery to induce anterior myocardial infarction by permanent coronary artery ligation or sham surgery. Infarcted rats were imaged with standard gadolinium delayed enhancement MRI (DEMRI) with inversion recovery techniques (DEMRI inversion recovery) as well as DEMRI T1 mapping. A subsequent MEMRI scan was performed 48 h later using either nonchelated or chelated manganese and T1 mapping. Finally, animals were culled at 12 weeks, and infarct size was quantified histologically with Masson's trichrome (MTC). Results: Both manganese agents induced concentration-dependent shortening of myocardial T1 values. This was greatest with nonchelated manganese, and could be inhibited by 30-43% with calcium-channel blockade. Manganese imaging successfully delineated the area of myocardial infarction. Indeed, irrespective of the manganese agent, there was good agreement between infarct size on MEMRI T1 mapping and histology (bias 1.4%, 95% CI -14.8 to 17.1 P>0.05). In contrast, DEMRI inversion recovery overestimated infarct size (bias 11.4%, 95% CI -9.1 to 31.8 P=0.002), as did DEMRI T1 mapping (bias 8.2%, 95% CI -10.7 to 27.2 P=0.008). Increased manganese uptake was also observed in the remote myocardium, with remote myocardial ∆T1 inversely correlating with left ventricular ejection fraction after myocardial infarction (r=-0.61, P=0.022). Conclusions: MEMRI causes concentration and calcium channel-dependent myocardial T1 shortening. MEMRI with T1 mapping provides an accurate assessment of infarct size and can also identify changes in calcium handling in the remote myocardium. This technique has potential applications for the assessment of myocardial viability, remodelling, and regeneration.

Resident cells of the myocardium: more than spectators in cardiac injury, repair and regeneration.

Multiple resident cell types contribute to maintaining the structure and physiological function of the heart over the life course. Cardiomyocyte proliferation supports scar free regeneration in the neonatal heart following injury, but a lower rate of proliferation in the adult necessitates replacement by a collagen scar to maintain ventricular integrity. In this short review we discuss recent studies that have identified novel roles for non-myocyte resident cells and the extracellular matrix in supporting repair, as well as cardiomyocyte and vascular regeneration, following myocardial infarction.

αv integrins on mesenchymal cells regulate skeletal and cardiac muscle fibrosis.

Mesenchymal cells expressing platelet-derived growth factor receptor beta (PDGFRß) are known to be important in fibrosis of organs such as the liver and kidney. Here we show that PDGFRß+ cells contribute to skeletal muscle and cardiac fibrosis via a mechanism that depends on αv integrins. Mice in which αv integrin is depleted in PDGFRß+ cells are protected from cardiotoxin and laceration-induced skeletal muscle fibrosis and angiotensin II-induced cardiac fibrosis. In addition, a small-molecule inhibitor of αv integrins attenuates fibrosis, even when pre-established, in both skeletal and cardiac muscle, and improves skeletal muscle function. αv integrin blockade also reduces TGFß activation in primary human skeletal muscle and cardiac PDGFRß+ cells, suggesting that αv integrin inhibitors may be effective for the treatment and prevention of a broad range of muscle fibroses.

Optical projection tomography permits efficient assessment of infarct volume in the murine heart postmyocardial infarction.

The extent of infarct injury is a key determinant of structural and functional remodeling following myocardial infarction (MI). Infarct volume in experimental models of MI can be determined accurately by in vivo magnetic resonance imaging (MRI), but this is costly and not widely available. Experimental studies therefore commonly assess injury by histological analysis of sections sampled from the infarcted heart, an approach that is labor intensive, can be subjective, and does not fully assess the extent of injury. The present study aimed to assess the suitability of optical projection tomography (OPT) for identification of injured myocardium and for accurate and efficient assessment of infarct volume. Intact, perfusion-fixed, optically cleared hearts, collected from mice 7 days after induction of MI by coronary artery occlusion, were scanned by a tomograph for autofluorescence emission after UV excitation, generating >400 transaxial sections for reconstruction. Differential autofluorescence permitted discrimination between viable and injured myocardium and highlighted the heterogeneity within the infarct zone. Two-dimensional infarct areas derived from OPT imaging and Masson's trichrome staining of slices from the same heart were highly correlated (r(2) = 0.99, P < 0.0001). Infarct volume derived from reconstructed OPT sections correlated with volume derived from in vivo late gadolinium enhancement MRI (r(2) = 0.7608, P < 0.005). Tissue processing for OPT did not compromise subsequent immunohistochemical detection of endothelial cell and inflammatory cell markers. OPT is thus a nondestructive, efficient, and accurate approach for routine in vitro assessment of murine myocardial infarct volume.

A Protocol for Improved Measurement of Arterial Flow Rate in Preclinical Ultrasound.

PURPOSE: To describe a protocol for the measurement of blood flow rate in small animals and to compare flow rate measurements against measurements made using a transit time flowmeter. MATERIALS AND METHODS: Measurements were made in rat and mice using a Visualsonics Vevo 770 scanner. The flow rate in carotid and femoral arteries was calculated from the time-average maximum velocity and vessel diameter. A correction factor was applied to correct for the overestimation of velocity arising from geometric spectral broadening. Invasive flow rate measurements were made using a Transonics system. RESULTS: Measurements were achieved in rat carotid and femoral arteries and in mouse carotid arteries. Image quality in the mouse femoral artery was too poor to obtain diameter measurements. The applied correction factor in practice was 0.71-0.77. The diameter varied by 6-18% during the cardiac cycle. There was no overall difference in the flow rate measured using ultrasound and using transit-time flowmeters. The flow rates were comparable with those previously reported in the literature. There was wide variation in flow rates in the same artery in individual animals. Transit-time measurements were associated with changes of a factor of 10 during the typical 40 min measurement period, associated with probe movement, vessel spasm, vessel kinking and other effects. CONCLUSION: A protocol for the measurement of flow rate in arteries in small animals has been described and successfully used in rat carotid and femoral arteries and in mouse carotid arteries. The availability of a noninvasive procedure for flow rate measurement avoids the problems with changes in flow associated with an invasive procedure.

Endothelial cell-specific ETB receptor knockout: autoradiographic and histological characterisation and crucial role in the clearance of endothelin-1.

Inactivation of endothelin B receptors (ETB), either through selective pharmacological antagonism or genetic mutation, increases the circulating concentration of endothelin-1 (ET-1), suggesting ETB plays an important role in clearance of this peptide. However, the cellular site of ETB-mediated clearance has not yet been determined. We have used a novel mouse model of endothelial cell-specific knockout (KO) of ETB (EC ETB(-/-)) to evaluate the relative contribution of EC-ETB to the clearance of ET-1. Phenotypic evidence of EC-specific ETB KO was confirmed by immunocytochemistry and autoradiography. Binding of the radiolabelled selective ETB ligand BQ3020 was significantly and selectively decreased in EC-rich tissues of EC ETB(-/-) mice, including the lung, liver, and kidney. By contrast, ETA binding was unaltered. RT-PCR confirmed equal expression of ET-1 in tissue from EC ETB(-/-) mice and controls, despite increased concentration of plasma ET-1 in EC ETB(-/-). Clearance of an intravenous bolus of [(125)I]ET-1 was impaired in EC ETB(-/-) mice. Pretreatment with the selective ETB antagonist A192621 impaired [(125)I]ET-1 clearance in control animals to a similar extent, but did not further impair clearance in EC ETB(-/-) mice. These studies suggest that EC-ETB are largely responsible for the clearance of ET-1 from the circulation.

Modeling heart rate regulation--part II: parameter identification and analysis.

In part I of this study we introduced a 17-parameter model that can predict heart rate regulation during postural change from sitting to standing. In this subsequent study, we focus on the 17 model parameters needed to adequately represent the observed heart rate response. In part I and in previous work (Olufsen et al. 2006), we estimated the 17 model parameters by minimizing the least squares error between computed and measured values of the heart rate using the Nelder-Mead method (a simplex algorithm). In this study, we compare the Nelder-Mead optimization method to two sampling methods: the implicit filtering method and a genetic algorithm. We show that these off-the-shelf optimization methods can work in conjunction with the heart rate model and provide reasonable parameter estimates with little algorithm tuning. In addition, we make use of the thousands of points sampled by the optimizers in the course of the minimization to perform an overall analysis of the model itself. Our findings show that the resulting least-squares problem has multiple local minima and that the non-linear-least squares error can vary over two orders of magnitude due to the complex interaction between the model parameters, even when provided with reasonable bound constraints.

The aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1) genes are not expressed in the rat heart.

Aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1) catalyze the production of aldosterone and corticosterone, respectively, in the rat adrenal cortex. Recently, there has been some debate as to whether these corticosteroids are also produced in the hearts of rodents and humans, possibly contributing to the development of hypertrophy and myocardial fibrosis. To investigate this, we have used our established, highly sensitive real-time quantitative RT-PCR method to measure CYP11B1 and CYP11B2 mRNA levels in adrenal and cardiac tissue from several rat models of cardiovascular pathology. We have also studied isolated adult rat ventricular myocytes treated with angiotensin II and ACTH. Total RNA was isolated from the adrenal and cardiac tissue of 1) male Wistar rats with heart failure induced by coronary artery ligation and sham-operated controls; 2) stroke-prone spontaneously hypertensive rats and Wistar Kyoto rats as controls; 3) cyp1a1Ren-2 transgenic rats and Fischer controls; 4) isolated adult Sprague-Dawley ventricular myocytes incubated with 11-deoxycorticosterone (DOC), DOC plus angiotensin II, or DOC plus ACTH. Adrenal CYP11B2 expression was significantly increased in transgenic rats compared with Fischer controls (1.3 x 10(9)+/- 1.2 x 10(9) vs. 2.1 x 10(7) +/- 7.0 x 10(6) copies/microg RNA; P < 0.05). There were no other significant differences in adrenal CYP11B2 or CYP11B1 expression between the model animals and their respective controls. Cardiac CYP11B1 and CYP11B2 mRNA transcript levels from all in vivo and in vitro groups were never greater than 100 copies per microgram total RNA and therefore too low to be detected reproducibly. This suggests that cardiac corticosteroid production is unlikely to be of any physiological or pathological significance.

Evaluation of a Revised Speech in Noise (RSIN) test.

A revised version of the Speech in Noise (SIN) test was developed by reallocating the recorded test material on the compact disc into different lists (blocks). The goal was to increase the equivalence and reliability of the test blocks to enhance their usefulness in research settings. The Revised Speech in Noise test has four blocks of sentences. Each block comprises twice as many sentences as in the original SIN test. There are also practice sentences for each condition. Forty-two elderly subjects with normal hearing for their age and gender provided data on the equivalence of the new test blocks. The remaining inequalities in mean scores were mostly eliminated using score weighting. Critical differences were developed to promote interpretation of scores from the same individual under different conditions. The revisions substantially improved the equivalence of test blocks and their sensitivity to performance changes. Increased test time is the associated drawback.

Human urotensin II increases coronary perfusion pressure in the isolated rat heart: potentiation by nitric oxide synthase and cyclooxygenase inhibition.

Urotensin II (U-II) is a cyclic peptide, recently cloned in man and present in cardiac tissue and arteries. The effects of human U-II (hU-II) on coronary perfusion pressure (CPP) were investigated in isolated rat hearts perfused retrogradely via the aorta at constant flow. hU-II produced a concentration-dependent increase in CPP (pEC50 8.6 +/- 0.3, n = 8), the maximum increase in CPP (12 +/- 4 mmHg) was obtained at 10(-7) M hU-II. At higher concentrations of hU-II CPP fell back towards baseline. Endothelin-1 produced a maximum increase in CPP of 63 +/- 11 mmHg within the concentration-range studied. Addition of the NO synthase inhibitor L N(G)nitro-arginine methyl ester (10(-4) M) and the cyclooxygenase inhibitor, indomethacin (10(-5) M) to the perfusion solution had no effect on the pEC50 value for hU-II, but significantly increased the maximum constriction (to 34 +/- 7 mmHg, n = 8, p < 0.05) and inhibited the later dilator response to hU-II. These results suggest that receptors for hU-II are present in the coronary vasculature and that smooth muscle contraction is modulated by the release of dilator factors, including NO and prostacyclin. Endothelial function is therefore likely to be of primary importance in modulating the coronary vasoconstrictor effects of hU-II in vivo.

Endothelium-derived hyperpolarizing factor and potassium use different mechanisms to induce relaxation of human subcutaneous resistance arteries.

This investigation examined the hypothesis that release of K(+) accounts for EDHF activity by comparing relaxant responses produced by ACh and KCl in human subcutaneous resistance arteries. Resistance arteries (internal diameter 244+/-12 microm, n=48) from human subcutaneous fat biopsies were suspended in a wire myograph. Cumulative concentration-response curves were obtained for ACh (10(-9) - 3x10(-5) M) and KCl (2.5 - 25 mM) following contraction with noradrenaline (NA; 0.1 - 3 microM). ACh (E(max) 99.07+/-9.61%; -LogIC(50) 7.03+/-0.22; n=9) and KCl (E(max) 74.14+/-5.61%; -LogIC(50) 2.12+/-0.07; n=10)-induced relaxations were attenuated (P<0.0001) by removal of the endothelium (E(max) 8.21+/-5.39% and 11.56+/-8.49%, respectively; n=6 - 7). Indomethacin (10 microM) did not alter ACh-induced relaxation whereas L-NOARG (100 microM) reduced this response (E(max) 61.7+/-3.4%, P<0.0001; n=6). The combination of ChTx (50 nM) and apamin (30 nM) attenuated the L-NOARG-insensitive component of ACh-induced relaxation (E(max): 15.2+/-10.5%, P<0.002, n=6) although these arteries retained the ability to relax in response to 100 microM SIN-1 (E(max) 127.6+/-13.0%, n=3). Exposure to BaCl(2) (30 microM) and Ouabain (1 mM) did not attenuate the L-NOARG resistant component of ACh-mediated relaxation (E(max), 76.09+/-8.92, P=0.16; n=5). KCl-mediated relaxation was unaffected by L-NOARG+indomethacin (E(max); 68.1+/-5.6%, P=0.33; n=5) or the combination of L-NOARG/indomethacin/ChTx/apamin (E(max); 86.61+/-14.02%, P=0.35; n=6). In contrast, the combination of L-NOARG, indomethacin, ouabain and BaCl(2) abolished this response (E(max), 5.67+/-2.59%, P<0.0001, n=6). The characteristics of KCl-mediated relaxation differed from those of the nitric oxide/prostaglandin-independent component of the response to ACh, and were endothelium-dependent, indicating that K(+) does not act as an EDHF in human subcutaneous resistance arteries.

Oestrogen and the cardiovascular system: the good, the bad and the puzzling.

The concept that oestrogen replacement therapy is cardioprotective has been challenged recently by the negative results of randomized clinical trials in coronary heart disease. These data have come at a time of rapid advances in our understanding of the cellular mechanisms of oestrogen. In particular, the cloning of the classical oestrogen receptor (ERalpha), the identification of a novel ER isoform (ERbeta), the availability of specific ERalpha and ERbeta knockout mice models, and the elucidation of receptor functions and signalling pathways linked to non-genomic actions of oestrogen are helping to unravel this complex biology. In this article, these advances will be discussed with particular emphasis on the regulation of nitric oxide synthesis by oestrogen. Furthermore, the puzzling issues that have emerged and the potential for development of novel and specific therapeutic approaches will be highlighted.

Verifying loudness perception after hearing aid fitting.

During the verification phase of a hearing aid fitting, clinicians often want to assess the extent to which loudness perceptions for amplified sounds are similar to those typical of normal hearers. This type of verification calls for a criterion for "normal" loudness perception of sounds presented in a sound field. This research sought to answer several questions about the parameters of a valid "normal" criterion for a verification procedure using the Contour test of loudness perception. Loudness data were obtained from 30 listeners with normal hearing. Results indicated that a loudness growth function obtained with earphone listening is not an appropriate normative reference for hearing aid fitting verification. Instead, the normative data should be based on sound field listening. Results also indicated that the same normative function could be used to assess both unilateral and bilateral fittings. Further, it is likely that the same normative function can be used for most frequency responses that are likely to be used in feasible fittings. Finally, it was found that a previously published normative function obtained using an automated test procedure was not faithfully replicated using a carefully executed fully manual test procedure. We concluded that, until a replicable normative function is established, practitioners will need to generate their own local norms to perform postfitting verification of loudness normalization.

Regulation of the myocardial endothelin system by angiotensin-II and losartan.

Evidence for interactions between the endothelin (ET) and renin-angiotensin systems is plentiful in vitro, but few studies have investigated these interactions in vivo. In the study reported here, we have investigated the influence of chronic angiotensin-II (A-II) infusion in vivo on expression of preproendothelin-1 (PPET-1) and endothelin-A- (ET(A)) and endothelin-B- (ET(B)) receptor mRNA in the heart. The role of the angiotensin type 1 (AT1)-receptor in mediating the actions of A-II was studied using losartan, the selective AT1-receptor antagonist. Male rats received an infusion of A-II (200 ng/kg/min) or vehicle for 14 days via mini-osmotic pumps; losartan (10 mg/kg/day) was administered in the drinking water. PPET-1 and ET(A)- and ET(B)-receptor mRNA were detected in heart sections using nonradioactive antisense in situ hybridization. Independent treatments with either A-II or losartan had no significant effect on PPET-1, ET(A)- or ET(B)-receptor expression. Combined treatment resulted in an increase in PPET-1 mRNA (p < 0.001) and ET(B)-receptor mRNA expression (p < 0.01), while ET(A)-receptor mRNA expression was decreased (p < 0.001). These results suggest that selective AT1-receptor blockade, in the presence of an elevated plasma A-II concentration, causes upregulation of ET-1 synthesis in the myocardium as well as modification of ET receptor expression. These effects may be mediated via angiotensin type 2 (AT2)-receptors.

Inducible nitric oxide synthase-derived superoxide contributes to hypereactivity in small mesenteric arteries from a rat model of chronic heart failure.

The aims of this study were to (a) determine whether inducible nitric oxide synthase (iNOS) is expressed in small mesenteric arteries from rats with chronic heart failure (CHF), (b) investigate the functional significance of this potential source of nitric oxide (NO) on vascular responsiveness and (c) investigate the role that superoxide plays in modulating vascular function in these arteries. CHF was induced in male Wistar rats by coronary artery ligation (CAL). In sham-operated rats the ligature was not tied but pulled under the artery. Six weeks after surgery CAL rats had left ventricular (LV) infarctions and elevated LV end-diastolic pressures. Immunoreactive iNOS was found in endothelial cells, vascular smooth muscle cells and in the adventitia of small mesenteric arteries from CAL rats but not those from sham-operated rats. Third order mesenteric arteries (300-350 microm) were mounted in a small vessel pressure myograph. Endothelium-intact arteries from CAL rats were more responsive to phenylephrine (PE) than arteries from sham-operated rats (pD(2) value, CAL, 6.2+/-0.1; sham-operated, 5.9+/-0.1, P<0.05). Both the selective iNOS inhibitor, N-(3-(Aminomethyl) benzyl) acetamidine dihydrochloride (1400W; 10(-6) M) and the superoxide dismutase mimetic, Mn [III] tetrakis [1-methyl-4-pyridyl] porphyrin, (MnTMPyP; 10(-4) M) reversed the hyperesponsiveness (pD(2) values, 1400W, 5.9+/-0.1; MnTMPyP, 5.81+/-0.1, P<0.05). The NOS substrate, L-arginine (10(-3) M), reduced responsiveness of endothelium-denuded small mesenteric arteries from CAL rats (P<0.01). None of these drugs altered responses to PE in arteries from sham-operated rats. In summary, this study demonstrates that iNOS is expressed in mesenteric arteries from rats with CHF. However, instead of generating large quantities of NO, iNOS appears to be generating superoxide, perhaps because of a deficiency in its substrate, L-arginine. Increased superoxide generation from iNOS contributes to the hyperesponsive nature of endothelium-intact small mesenteric arteries from rats with CHF.

Localization and function of ET-1 and ET receptors in small arteries post-myocardial infarction: upregulation of smooth muscle ET(B) receptors that modulate contraction.

Endothelin-1 (ET-1) has been implicated as a mediator of increased vascular tone during development of heart failure post-myocardial infarction (MI). In the present study, expression and pharmacology of ET-1 and its receptors were studied in small mesenteric arteries from rats at 5 and 12 weeks after coronary artery ligation for induction of MI, or sham-operation. In vessels from sham-operated and 5 week post-MI rats preproET-1mRNA, immunoreactive (ir) ET-1, ET(B) receptor mRNA and irET(B) receptor were confined to the endothelium, while ET(A) receptor mRNA was distributed throughout the media. At 12 weeks post-MI, preproET-1 and irET(A) receptor localization was similar but ET(B) receptor mRNA and immunoreactivity were detectable in the media, as well as the endothelium. The ET-1 concentration-response curve (CRC) was progressively shifted to the right in pressurized third generation mesenteric arteries from 5 and 12 week post-MI rats relative to sham-operated rats, with no change in the maximum. The ET(A) receptor antagonist BQ-123 (10(-6) M) induced a rightward shift of the ET-1 CRC in all vessels. Desensitization of ET(B) receptors, by exposure to SRTX S6c (3x10(-8) M), had no effect on the ET-1 CRC in vessels from 5 week post-MI or sham-op rats but induced a leftward shift in vessels from 12 week post-MI rats. These results identify the endothelium as the primary site of ET-1 synthesis in small arteries and the ET(A) receptor as mediating the effects of ET-1 in these vessels. However, ET(B) receptor expression increases in vascular smooth muscle post-MI and is linked to mechanisms that inhibit the contractile response to ET-1.