Biomedical subjects

O Zolk

Publications and source records attributed to O Zolk.

27 records · Page 2Linked to original sources

PubMed1998

Effects of quinapril, losartan and hydralazine on cardiac hypertrophy and beta-adrenergic neuroeffector mechanisms in transgenic (mREN2)27 rats.

1. Desensitization of the myocardial beta-adrenergic signal transduction pathway is an important mechanism which is involved in the progression of hypertensive heart disease. The aim of the present study was to evaluate the differential effects of chronic pharmacotherapy with an angiotensin converting enzyme (ACE)-inhibitor, an AT1-receptor antagonist and a direct vasodilator on blood pressure, cardiac hypertrophy and the beta-adrenergic signal transduction. Therefore, transgenic TG(mREN2)27 (TG) rats overexpressing the mouse renin gene were used. This strain is characterized by the development of fulminant hypertension with cardiac hypertrophy. 2. Seven week old heterozygous TG(mREN2)27 rats were treated for 11 weeks with the AT1-receptor antagonist losartan (10 mg kg[-1]), the ACE-inhibitor quinapril (15 mg kg[-1]) and the direct vasodilator hydralazine (30 mg kg[-1]). Untreated TG and normotensive Sprague-Dawley rats (SD) served as controls. 3. TG(mREN2)27-rats were characterized by arterial hypertension (TG 194+/-3.2 mmHg vs SD 136+/-2.9 mmHg systolic blood pressure), increased left ventricular weights (TG 4.3+/-0.3 vs SD 3.0+/-0.1 mg g(-1) body weight), decreased myocardial neuropeptide Y (NPY) concentrations (TG 1143+/-108 vs SD 1953+/-134 pg g(-1) wet weight), reduced beta-adrenoceptor densities (TG 51.1+/-1.9 vs SD 63.4+/-3.7 fmol mg[-1]) as assessed by [125I]-cyanopindolol binding studies, and increased Gi(alpha)-activities (TG 4151+/-181 vs SD 3169+/-130 densitometric units) as assessed by pertussis toxin catalyzed [32P]-ADP-ribosylation. Downregulation of beta-adrenoceptors and increased Gi(alpha) were accompanied by significantly reduced isoprenaline-, Gpp(NH)p- and forskolin-stimulated adenylyl cyclase activity. Catalyst activity as determined by forskolin plus Mn2+ co-stimulation of adenylyl cyclase did not differ between TG(mREN2)27- and SD control-rats. 4. Losartan and quinapril significantly restored systolic blood pressures, left ventricular weights, beta-adrenoceptor densities, myocardial neuropeptide Y-concentrations, adenylyl cyclase activities and Gi(alpha)-activities towards the values in Sprague-Dawley-controls. No differences were observed between the effects of quinapril- and losartan-treatment. In contrast, hydralazine had only minor effects on blood pressure reduction, regression of left ventricular hypertrophy and neuroeffector defects in TG(mREN2)27. 5. In conclusion, direct vasodilatation is not able to overcome the pathophysiological alterations in TG caused by transgene overexpression. In contrast, ACE-inhibitors and AT1-receptor antagonists, which inhibit the renin angiotensin system, equally exert beneficial effects on blood pressure, myocardial hypertrophy and neuroeffector mechanisms. Modulation of the sympathetic tone and resensitization of the beta-adrenergic signal transduction system may contribute to the special effectiveness of these drugs in the treatment of the hypertensive cardiomyopathy.

Adenylyl Cyclases↗

PubMed1998

Effects of angiotensin II type 1 receptor blockade and angiotensin-converting enzyme inhibition on cardiac beta-adrenergic signal transduction.

Inhibition of the renin-angiotensin system has been shown to improve symptoms and prognosis in heart failure. We compared the effects of inhibition of angiotensin-converting enzyme or blockade of angiotensin II type 1 (AT1) receptors in a model with renin-induced hypertension that is known to exhibit similar changes in sympathetic activation and beta-adrenergic desensitization, as observed in heart failure. Treatment with captopril (100 mg/kg of feed) or the AT1-antagonist Bay 10-6734 (100 mg/kg of feed) was performed in transgenic rats harboring the mouse renin 2d gene [TG(mREN2)27]. Neuropeptide Y and angiotensin II levels, adenylyl cyclase activity, beta-adrenergic receptors, G(salpha), and G(ialpha) were investigated. TG(mREN2)27 showed a depletion of myocardial neuropeptide Y stores and an increase in myocardial angiotensin II concentrations. Isoprenaline- and guanylylimidodiphosphate-stimulated adenylyl cyclase activities and beta-adrenergic receptor density were reduced, whereas the catalyst and G(salpha)-function were unchanged. G(ialpha) protein and mRNA concentrations were increased. All alterations were normalized by both treatments. Systolic left ventricular pressures, plasma atrial natriuretic peptide, and myocardial steady state atrial natriuretic peptide mRNA concentrations and heart weights were similarly reduced by both treatments. Sympathetic neuroeffector defects are similarly reversed by angiotensin-converting enzyme inhibition or AT1 antagonism. The data support the concept that pharmacological interventions in the myocardial renin-angiotensin system significantly reverse local sympathetic neuroeffector defects. This could be important for the beneficial effects of these agents.

Adenylyl Cyclases↗

PubMed1998

Vascular beta-adrenergic receptor adenylyl cyclase system from renin-transgenic hypertensive rats.

In transgenic rats harboring the mouse Ren-2d gene [TG(mREN2)27], downregulation of the myocardial beta-adrenergic receptor adenylyl cyclase system has been demonstrated previously. Because a reduced vasodilatory reactivity may significantly contribute to hypertension in this model of an activated tissue renin-angiotensin system, the present study investigated alterations of the vascular beta-adrenergic receptor adenylyl cyclase system. In freshly harvested aortas from transgenic rats, the activity of adenylyl cyclase was reduced significantly (P<.05) in the presence of isoprenaline (10 micromol/L; -28+/-4.5%), guanosine 5'-triphosphate, 5'-guanylylimidodiphosphate [Gpp(NH)p] (100 micromol/L; -29+/-4.7%), and forskolin (100 micromol/L) with (-42+/-6%) and without (-40+/-4.3%) MnCl2. Densities of beta-adrenoceptors were similar in both strains. In situ hybridization demonstrated the expression of the transgene in aortic smooth muscle cells. These data indicate a reduced catalyst function as a major contributing factor involved in the maintenance of high blood pressure in TG(mREN2)27. However, in cultivated aortic smooth muscle cells, cAMP production after stimulation with isoprenaline, forskolin, and Gpp(NH)p in the presence or absence of MnCl2 was not different. Affinities and densities of beta-adrenoceptors and amounts of immunochemically detected inhibitory and stimulatory G-protein alpha-subunits were unchanged. Desensitization after incubation with 10 micromol/L isoprenaline for 72 hours was identical in smooth muscle cells from both strains. Cell cultivation and isoprenaline treatment had no effect on transgene expression. We concluded that in transgenic rats the downregulation of the aortic beta-adrenergic adenylyl cyclase system is due to humoral and hemodynamic factors present in vivo rather than to transgenicity itself.

Adenylyl Cyclases↗

PubMed1998

Salt induces vascular AT1 receptor overexpression in vitro and in vivo.

The molecular events governing salt-sensitive hypertension are currently unknown. Because the renin-angiotensin system plays a central role in blood pressure regulation, as well as electrolyte balance, it may be closely involved in the phenomenon of salt sensitivity. Therefore, we examined the effect of a high salt diet (8%) on aortic angiotensin type 1 (AT1) receptor expression in Sprague-Dawley rats by means of radioligand binding assays and quantitative polymerase chain reaction. High salt intake caused an increase of AT1 receptor mRNA and AT1 receptor density to approximately 160% compared with control levels. Northern analysis revealed that incubation of vascular smooth muscle cells (VSMCs) with an increased concentration of sodium chloride (by 10 mmol/L) caused a time-dependent elevation of AT1 receptor mRNA levels, with a maximum of 241+/-28% after 24 hours. There was a similar increase in AT1 receptor density in VSMCs in response to sodium chloride, as assessed by radioligand binding assays. The salt-induced AT1 receptor upregulation led to an enhanced functional response of VSMCs on stimulation with angiotensin II, since the angiotensin II-elicited intracellular calcium response was significantly increased in cells preincubated for 24 hours with the high salt concentration. Thus, sodium chloride may directly induce AT1 receptor upregulation in vitro as well as in vivo; this suggests a potential mechanism participating in salt-induced hypertension because the AT1 receptor activation is tightly coupled to blood pressure regulation.

Analysis of Variance↗

PubMed1998

Chamber-specific alterations of norepinephrine uptake sites in cardiac hypertrophy.

The present study investigated local differences of sympathetic activation and sympathetic neuroeffector defects in nonhypertrophied right and hypertrophied left ventricles in a rat model with renin-induced pressure overload [TG(mREN2)27]. As judged from the depletion of myocardial norepinephrine stores, sympathetic activation was more pronounced in the left than in the right ventricles. In addition, norepinephrine uptake1 carrier sites were reduced in left but unchanged in right ventricles. Gene expression of the carrier was unchanged in stellate ganglia. An increase of Gialpha expression and a heterologous adenylyl cyclase desensitization occurred only in the left but not in the right ventricles, whereas a reduction of beta-adrenergic receptors was observed in both chambers. We concluded that general sympathetic activation can lead to beta-adrenoceptor downregulation but that pressure overload further increases sympathetic activation involving norepinephrine uptake mechanisms in the left ventricles, resulting in heterologous beta-adrenergic desensitization.

Adenylyl Cyclases↗

PubMed1997

The role of Gi-proteins and beta-adrenoceptors in the age-related decline of contraction in guinea-pig ventricular myocytes.

A decline in contractility in myocytes from ageing guinea-pig hearts was demonstrated, which is more pronounced for maximum beta-adrenoceptor-stimulated activity than contraction in high Ca2+. In this study the role of the inhibitory G-proteins (Gi) in this process was investigated. Comparisons were made between young (Y, < 400 g, < 4 weeks), adult (A. > 600 g, > 8 weeks) and senescent guinea pigs (S, 58-65 weeks, 1136 +/- 30 g). Gi alpha activity, detected by pertussis toxin-catalysed ADP ribosylation, was significantly increased in senescent compared to young animals, but immunodetectable levels of Gi alpha were unchanged, beta-adrenoceptor number was decreased by 27% in senescent compared with young animals (P < 0.002). Pertussis toxin treatment increased the maximum response to isoproterenol in contacting myocytes so that there was no longer any significant decline with age. Maximum contraction amplitudes (sarcomere length change, micron) with isoproterenol before pertussis toxin were 0.144 +/- 0.011 (Y, n = 22 animals), 0.104 +/- 0.009 (A. 18) and 0.098 +/- 0.009 (S. 14), P < 0.01 by analysis of variance (ANOVA). Following toxin treatment amplitudes were 0.140 +/- 0.012 (Y. 12), 0.117 +/- 0.010 (A. 10) and 0.117 +/- 0.018 (S. 8), P = N.S. Pertussis toxin treatment also reversed the effects of ageing on contraction and relaxation velocity in isoproterenol. In contrast, the effect of age on contraction amplitude or velocity in maximum Ca2+ was more pronounced after toxin treatment. The EC50 value for isoproterenol increased with age: pertussis treatment decreased the EC50 in each group, but the effect was especially pronounced for senescent animals. There was no significant difference in the concentration-response curves for the negative inotropic effect of adenosine (in the presence of isoprotenerol) between the three age groups before toxin treatment. All effects of adenosine were abolished after pertussis exposure. We conclude that increased Gi alpha activity is likely to contribute to the decreased response to isoproterenol, but not to high Ca2+, in myocytes from ageing guinea-pigs.

Adenosine Diphosphate↗

PubMed1997

Angiotensin receptor antagonism and angiotensin converting enzyme inhibition improve diastolic dysfunction and Ca(2+)-ATPase expression in the sarcoplasmic reticulum in hypertensive cardiomyopathy.

BACKGROUND: Hypertensive cardiomyopathy is a major risk factor for the development of chronic heart failure. OBJECTIVE: To investigate whether treatment with an angiotensin converting enzyme inhibitor (ACEI) or with an angiotensin type 1 receptor antagonist (AT1-RA) is sufficient to prevent the development of hypertensive cardiomyopathy and cardiac contractile dysfunction. Special emphasis was placed on the effects of both treatments on sarcoplasmic reticulum Ca(2+)-ATPase (SERCA 2a) gene expression as a major cause of impaired diastolic cardiac relaxation. METHODS AND RESULTS: Eight-week-old rats harboring the mouse renin 2d gene [TG(mREN2)27] were treated for 8 weeks with 100 mg/kg captopril (Cap) in their food and 100 mg/kg of the AT1-RA Bay 10-6734 (Bay) in their food. Untreated TG(mREN2)27 and Sprague-Dawley rats (SDR) were used as controls. Both treatment regimens normalized the left ventricular weight, which was increased significantly (P < 0.001) in TG(mREN2)27. Both treatments normalized the left ventricular end-systolic and end-diastolic pressures, which were significantly (P < 0.001) higher in TG(mREN2)27 than they were in SDR, and they improved the velocity of the decrease in pressure [P < 0.05, Bay and Cap versus TG(mREN2)27]. Decreased left ventricular SERCA 2a mRNA and protein levels and increased atrial natriuretic peptide messenger RNA levels were normalized by Bay and Cap treatments (P < 0.05, Bay and Cap versus TG(mREN2)27, by Northern and Western blotting). According to radioimmunoassay and an enzyme assay, respectively, Bay, but not Cap, increased plasma angiotensin I concentrations and the renin activity above normal levels (P < 0.05), whereas myocardial angiotensin II concentrations (determined by radioimmunoassay), which were significantly (P < 0.05) increased in TG(mREN2)27, were normalized equally by Bay and Cap. CONCLUSIONS: In renin-induced hypertensive cardiomyopathy, left ventricular diastolic dysfunction occurs at the stage of compensated myocardial hypertrophy. The decreased left ventricular relaxation velocity might be due to reduced SERCA 2a gene expression. In this model of hypertensive cardiomyopathy, AT1-RA and ACEI treatments are similarly effective at reducing the arterial pressure, preventing myocardial hypertrophy and diastolic contractile dysfunction. Normalization of SERCA 2a gene expression, either by AT1-RA or by ACEI treatment, might contribute to the improvement in diastolic function.

Angiotensin I↗

PubMed1997

Hypercholesterolemia is associated with enhanced angiotensin AT1-receptor expression.

Low-density lipoprotein increases the AT1-receptor gene expression in vascular smooth muscle cells. To elucidate whether elevated cholesterol serum levels upregulate the AT1 receptor and its functional response to angiotensin II in vivo, we compared 1) the vasoconstrictive effect of angiotensin II and 2) the level of expression of the vascular AT1 receptor in aortas of normocholesterolemic and hypercholesterolemic rabbits. Contraction experiments on isolated aortic rings showed that the angiotensin II-induced vasoconstriction was increased in hypercholesterolemic New Zealand White rabbits compared with normocholesterolemic New Zealand White rabbits. This difference in the angiotensin II-induced vasoconstriction was caused by a twofold increase in the density of cell surface AT1 receptors in hypercholesterolemic rabbits, as assessed by radioligand binding assays. The enhanced expression of AT1 receptors on the surface of these vascular cells was caused by elevated steady-state levels of the AT1-receptor mRNA to 220 +/- 35% in aortas excised from hypercholesterolemic rabbits compared with levels in aortas from normocholesterolemic rabbits, as measured by Northern blot analysis. These data indicate that hypercholesterolemia is associated with upregulation of expression and function of vascular AT1 receptors in vivo. This suggests a novel mechanism by which hypercholesterolemia could be involved in the onset and progression of chronic vascular diseases such as hypertension and arteriosclerosis if the phenomenon is confirmed in humans.

Angiotensin II↗

PubMed1997

Contractile systolic and diastolic dysfunction in renin-induced hypertensive cardiomyopathy.

The present study investigated whether functional, molecular, and biochemical alterations occurring in chronic heart failure can already be detected in compensated hypertensive cardiac hypertrophy. Force of contraction (isolated papillary muscle strip preparations), sarcoplasmic reticulum (SR) protein and myosin heavy chain isoform expression (Northern and Western blot analysis), myocardial fibrosis (collagen stains, hydroxyproline quantification), myocardial renin mRNA (RT-PCR), and angiotensin II levels and plasma aldosterone concentrations (radioimmunoassay) were studied in hypertrophied myocardium from transgenic rats harboring the mouse Ren-2d gene. Contraction and relaxation velocities of isolated papillary muscle strips were significantly reduced in cardiac hypertrophy. The beta-/alpha-myosin heavy chain ratio was significantly increased in the hypertrophied left ventricles, whereas SR Ca2+-ATPase (SERCA 2a) and phospholamban mRNA and protein levels were significantly decreased. The decrease in SERCA 2a was more pronounced than the decrease in phospholamban levels. There was no increased myocardial fibrosis. Left ventricular myocardial renin mRNA and angiotensin II concentrations, as well as plasma aldosterone levels, were higher in transgenic than in control rats. In hypertensive cardiac hypertrophy, myosin heavy chain isoform shift and reduction of SR protein levels are related to systolic and diastolic dysfunction, respectively. These alterations precede the development of myocardial fibrosis. Increased myocardial renin mRNA and angiotensin II concentrations suggest that an activated tissue renin-angiotensin system might contribute to these alterations. Since the alterations in compensated cardiac hypertrophy apparently precede those in chronic heart failure, they might accelerate the transition from hypertrophy to failure and could therefore be targets for pharmacological interventions.

Angiotensin II↗