Association of the heart rate turbulence with classic risk stratification parameters in postmyocardial infarction patients.

The heart rate turbulence (HRT) parameters were introduced for risk stratification of ventricular arrhythmias in postmyocardial infarction patients. However, the relationship of these parameters with other risk stratificators such as heart rate variability (HRV), repolarization parameters or left ventricular function is unknown. Furthermore, the influence of age and medication on HRT remains to be evaluated. Holter ECG's of 509 post-MI patients (1-10 years after MI) were screened for single ventricular extrasystole. In 196 patients the parameters' turbulence onset (TO) and turbulence slope (TS) could be computed. A pathological TO (>0%) and TS (<2.5 ms) was found in 58 and 54 patients, respectively. HRT was not related to gender, but was correlated with age (TS: r = 0.209, P < 0.01). No relationship was observed between QT interval, QTc interval or QT dispersion and HRT parameters. Individuals with a pathological HRT showed decreased HRV values (e.g., PNN50: 2.8 vs. 11.5; P < 0.001). Of all MI patients with systolic left ventricular dysfunction (EF < 45%, n = 46), 18 showed a pathological TO (39%) compared to 34 out of 142 patients (24%) with an EF > 45%. In contrast, the percentage of pathological HRT was not different between patients with left ventricular hypertrophy (16 out of 59, 27%) compared to patients without LVH (38 out of 133, 28%). The HRT was pathological in 14 out of 24 patients with diabetes mellitus (58%) compared to 40 out of 172 (23%) normoglycemic patients (TO: -0.6 +/- 3.1 vs. -2.5 +/- 5.5, P < 0.02). HRT was similar in patients with ss-blockers (n = 96) as in patients without ss-blockers (n = 100). In stable post-MI patients, HRT is influenced by age and left ventricular function and correlates with heart rate variability. Therapy with ss-blockers has no influence on HRT, while diabetic patients may have an increased likelihood of pathological HRT.

Myocardial IL-6 regulation by neurohormones--an in vitro superfusion study.

BACKGROUND: Interleukin-6 (IL-6) is expressed in the myocardium and has been implicated in cell proliferation, negative inotropic effects and myocardial hypertrophy. To determine whether myocardial IL-6 is modified by neurohumoral and immunoregulatory stimuli, we studied the effects of lipopolysaccharide (LPS), corticosterone (CS), isoproterenol and angiotensin II on myocardial IL-6 secretion in superfused myocardium. METHODS: Slices of rat left ventricular myocardium were superfused in 80 microl chambers for up to 5h. LPS (1, 50, and 100 microg/ml), CS (10(-7), 10(-6), and 10(-5)M, DSMO as vehicle), isoproterenol (10(-6), 10(-7), and 10(-8)M) and angiotensin II (10(-5), 10(-7), and 10(-9)M) were added to the culture medium at hour 2. IL-6 was measured in the perfusate by ELISA. RESULTS: Physiological corticosterone concentrations (10(-7)M) resulted in an increase in IL-6 concentration (142%) while high doses of steroid decreased IL-6 significantly (CS 10(-6)M: 88+/-14%,p<.05; CS 10(-5): 91+/-9%,p<.05) after 5h. Left ventricular IL-6 secretion was significantly stimulated by LPS 50 microg/ml (3262+/-1684% vs. CTRL: 116+/-34%, p<.01). Isoproterenol treatment increased in IL-6 secretion compared to controls with and without CS, while angiotensin II reduced IL-6 concentration only in combination with CS. CONCLUSION: Myocardial IL-6 secretion is modulated by physiological concentrations of corticosterone or angiotensin II and can be induced by LPS or isoproterenol, indicating a tight regulation of this cytokine. Suppression of cytokine expression within the heart might be a potential therapeutic goal in the treatment of various cardiovascular diseases.

Systemic immunosuppression fails to suppress cardiac cytokine induction in pressure overload hypertrophy in rats.

BACKGROUND: Activation of cytokines such as interleukin-6 (IL-6) has been implicated in the pathogenesis of left ventricular dysfunction and hypertrophy since they have been shown to mediate cell proliferation, negative inotropic effects and myocardial hypertrophy. However, the effects of immunosuppressive therapy on cytokines in the treatment of heart failure and hypertrophy are unclear. AIMS: To test the hypothesis that systemic immunosuppresion may influence serum and myocardial IL-6 and, thereby, may affect progression of myocardial hypertrophy. We studied the effects of chronic treatment with methotrexate (MTx) and with the ACE inhibitor ramipril on IL-6 in rats with pressure overload left ventricular hypertrophy (LVH) due to aortic banding. METHODS: Animals were treated with either vehicle (n = 6) or methotrexate (MTx 1: 0.3 mg/kg BW/week; MTx 2: 0.9 mg/kg BW/week; i.p.; n = 6 each group) once a week during weeks 4-12 after aortic banding; sham-operated rats served as controls (CTRL; n = 8). During the development of LVH, serum IL-6 was determined by rat-specific ELISA and 12 weeks after aortic banding myocardial IL-6 was measured using a tissue superfusion technique or determining of protein concentration. RESULTS: Aortic banding significantly lowered blood pressure, increased left ventricular weight and resulted in elevated serum IL-6 levels (27.6 +/- 5.1 vs 19.1 +/- 2.3 pg/ml, p < 0.05) compared to CTRL. MTx treatment normalised the initially elevated serum IL-6 levels after 8 weeks of treatment. The significant increase in IL-6 concentration in the superfusate of all aortic banding groups compared to CTRL (< 30%, p < 0.05) was not altered by prior MTx therapy. Accordingly, both doses of MTx failed to prevent LVH progression (1.67 +/- 0.23 g vs. 2.32 +/- 0.31 g, p < 0.05). In contrast, chronic inhibition of the RAAS not only prevents LVH but also reduces myocardial IL-6 concentration (6898 +/- 355 vs. 3073 +/- 366 pg/mg protein, p < 0.05). CONCLUSION: Pressure overload LVH in rats is characterized by an increase in serum levels of IL-6 as well as myocardial IL-6. Chronic immunosuppressive therapy normalized systemic IL-6 levels, but failed to reduce cardiac IL-6 expression and the progression of LVH, while ACE inhibition is sufficient to modify LVH and thereby normalises myocardial IL-6 expression.

Molecular cloning and functional characterization of the upstream rat atrial natriuretic peptide promoter.

OBJECTIVE: The upregulation of left ventricular atrial natriuretic peptide (ANP) serves as a molecular marker of cardiac hypertrophy. The precise mechanisms underlying this gene induction are unclear, since the presently cloned 3.6 kilo base (kb) rat ANP promoter failed to substantially induce coupled reporter genes in chronically hypertrophied hearts. The aim of this study was to clone and to functionally analyse the upstream ANP promoter. DESIGN: Upstream of the known ANP promoter, a 1.5 kb segment was cloned by the promoter walker method and found to harbour a putative CCAAT-binding site as well as multiple putative transcription factor binding sites. This newly cloned segment was ligated with a reporter gene, in vivo transfected into rat myocardium, and analysed under basal conditions or after stimulation with both acute (isovolumetric contractions in the Langendorff apparatus) and chronic wall stress (aortic banding). RESULTS: Reporter gene constructs carrying the newly cloned segment conferred only little promoter activity. In hearts exposed to acute wall stress, the previously cloned 3.6 kb ANP promoter as well as a constitutive promoter (pGL3 promoter vector) were active but markedly suppressed after extension with the newly cloned upstream promoter (-88.1 and -85.5%; P < 0.05 respectively). Site directed mutagenesis of two AP-2 transcription factor binding sites (base pairs -3946 to -3954 or -4192 to -4200) eliminated this silencing effect. In hearts with chronic pressure overload hypertrophy as well as in normal, unstimulated hearts the activity of the 3.6 kb ANP promoter was weak and also abolished after ligation with the 1.5 kb upstream segment. Moreover, both putative AP-2 binding sites within the upstream rat ANP promoter bound specifically to nuclear proteins of unstimulated, acute and chronic pressure overloaded hearts as demonstrated by electrophoresis mobility shift assays. CONCLUSION: Novel silencer elements were cloned, localized to two AP-2 binding sites in the upstream ANP promoter, and functionally characterized. Given that the putative upregulation of left ventricular ANP by the extensively studied 3.6 kb proximal promoter region is substantially diminished by the newly cloned segment, the functional significance of regulatory elements within the proximal promoter region should be re-evaluated. The molecular mechanism causing ANP mRNA induction in left ventricular hypertrophy remains obscure.