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Biomedical subjects

V Petrov

Publications and source records attributed to V Petrov.

At least 37 records · Page 2Linked to original sources
PubMed1999

Antagonism of the renin-angiotensin-aldosterone system and collagen metabolism in cardiac fibroblasts.

The renin-angiotensin-aldosterone system has emerged as a potential candidate for the accumulation of collagen in cardiac fibroblasts. The traditional renin-angiotensin-aldosterone system can be considered a system in which circulating angiotensin II or aldosterone is delivered to target tissue or cells. However, an independent local renin-angiotensin system has also been described in cardiac cells and evidence has been accumulated for autocrine and/or paracrine pathways by which biological actions of angiotensin II can be mediated. These actions of angiotensin II are primarily mediated through angiotensin II receptors of the subtype I (AT1). When evaluating the effects of angiotensin II in situ, changes in circulating levels and local production both have to be taken into account. Functional angiotensin II receptors have been documented in cardiac fibroblasts although the presence of aldosterone receptors in cardiac fibroblasts is obscure, and the expression of mRNA for mineralocorticoid receptors in cardiac fibroblasts has been described. In vitro, angiotensin II increased cardiac fibroblast-mediated collagen synthesis and mRNA levels of collagen type I, type III, pro-alpha 1 (I) collagen, pro-alpha 1 (III) collagen and fibronectin, and inhibited matrix metalloproteinase I activity. The ability of angiotensin II to induce collagen synthesis and expression of collagen in cardiac fibroblasts may be mediated by an increase in transforming growth factor-beta 1 in an autocrine/paracrine fashion. The angiotensin II-stimulated secretion and expression of collagen was completely abolished by AT1 receptor antagonism, but not affected by AT2 receptor antagonism. The discordant findings that have been reported concerning the in vitro effect of aldosterone on collagen synthesis in cardiac fibroblasts can at least partly be attributed to differences in methodology such as the use of the total population or a sub-population of cardiac fibroblasts. In vivo, chronic infusion of angiotensin II or aldosterone increased the collagen volume fraction in the ventricles. Angiotensin-converting enzyme (ACE) inhibition and AT1 receptor antagonism, but not AT2 receptor antagonism, reduced collagen deposition in the myocardium in spontaneously hypertensive rats. The cardioprotective mechanism of action of ACE inhibitors can be attributed to local blockade of the formation of angiotensin II, to the degradation of bradykinin or to the release of nitric oxide and/or eicosanoids. Angiotensin-converting enzyme inhibitors also reduced collagen deposition in rat myocardium following myocardial infarction suggesting that collagen deposition may in part result from mechanisms other than through AT1 receptors. However, further research is necessary to unravel the various mechanisms involved in the action of angiotensin-converting enzyme inhibitors or of AT1 receptor antagonists on collagen deposition in the myocardium.

Animals↗
PubMed1999

Proliferation of human peripheral blood mononuclear cells during calcium entry blockade. Role of protein kinase C.

To evaluate the role of protein kinase C (PKC) and intracellular calcium and particularly Ca(2+)-uptake in the initiation of lymphocyte mitogenesis, the proliferation of human peripheral blood mononuclear cells (PBMC) was investigated during calcium entry blockade with nifedipine (an L-type calcium channel blocker) and mibefradil (an L- and T-type calcium channel blocker with a higher selectivity for T-type channels). The rate of [3H]-thymidine, [3H]-uridine and [3H]-leucine incorporation into control and concanavalin A-stimulated PBMC cultured for 3 days in the presence or absence of the calcium channel blockers nifedipine or mibefradil (1, 10 or 50 microM) is assayed. Nifedipine and mibefradil concentration-dependently reduced cell number and [3H]-thymidine incorporation or de novo DNA synthesis in control and concanavalin A-stimulated PBMC, as well as de novo RNA and protein synthesis. The proliferative response of nifedipine- or mibefradil-treated cells was restored by addition of phorbol-12-myristate-13-acetate (PMA), an exogenous PKC activator. Our data show that PBMC treated with the Ca2+ channel blockers nifedipine or mibefradil are still capable of proliferating in response to PMA. However, in PKC-depleted cells, the proliferative response of PBMC was suppressed.

Adult↗
PubMed1999

Antagonism of the renin-angiotensin system, hypertrophy and gene expression in cardiac myocytes.

In response to humoral and mechanical stimuli, the myocardium adapts to increased work load through hypertrophy of individual muscle cells. Myocardial hypertrophy is characterized by an increase in cell size in the absence of cell division and is accompanied by changes in gene expression. Angiotensin II (Ang II), the effector peptide of the renin-angiotensin system (RAS), regulates volume and electrolyte homeostasis and is involved in cardiac and vascular growth in rats. In this review, the role of RAS in myocyte protein synthesis (myocyte hypertrophy) and in induction of gene expression will be discussed in rat cardiomyocytes in culture. Traditional RAS can be considered as a system in which circulating Ang II is delivered to target tissues or cells. However, a local RAS has also been described in cardiac cells and evidence has been accumulated for autocrine and/or paracrine pathways by which biological actions of Ang II can be mediated. These actions of Ang II are primarily mediated through Ang II receptors subtype I (AT1-R). When evaluating the effects of Ang II in situ, both changes in circulating levels and local production have to be taken into account. Contrasting results have been found concerning the in vitro effect of Ang II on the protein synthesis in cardiac myocytes and can be at least partly be attributed to methodological problems such as assay of de novo protein synthesis and isolation and separation procedure of cardiac myocytes. The Ang II-induced hypertrophic effect also depends on the existence of nonmyocytes in a cardiocyte culture. In rat cardiocytes, AngII also causes induction of many immediately-early genes (c-fos, c-jun, jun-B, Egr-1 and c-myc) and induces also late markers of cardiac hypertrophy (skeletal alpha-actin and atrial natriuretic peptide expression) and growth factors (TGF-beta 1 gene expression). In vivo AngII via AT1-R, causes not only ventricular hypertrophy but also a shift to the fetal phenotype of the myocardium. Angiotensin-converting enzyme inhibitors and AngII receptor antagonists of the subtype I not only induce the regression but also prevent the development of cardiac hypertrophy in experimental rat models.

Animals↗
PubMed1998

Protein kinase C induced changes in erythrocyte Na+/H+ exchange and cytosolic free calcium in humans.

To investigate the interrelationship between erythrocyte Na+/H+ exchange rate and free cytosolic Ca2+ concentration, the effect of the (non)selective protein kinase C inhibitors staurosporine, Ro 31-8220 and CGP 41251 (1 micromol/L) and of the protein kinase C activator phorbol-12-myristate-13-acetate (PMA, 1 micromol/L) was studied in vitro on these variables. PKC depleted erythrocytes were obtained after 24 h PMA down-regulation of the cells and intracellular Ca2+ clamping was obtained using quin-2 AM and fluo-3 AM. PMA increased (P < .05) the erythrocyte Na+/H+ exchange activity and this rise was accompanied by an increase in the free cytosolic Ca2+ concentration. When staurosporine and Ro 31-8220 were added to erythrocytes in suspension, a decrease in free cytosolic Ca2+ concentration was also found, whereas no significant change was observed after CGP 41251 administration. The Na+/H+ exchange rate was decreased in the 24 h PMA down-regulated erythrocytes as well as in Ca2+-clamped cells. Addition of Ca2+ in a concentration range of 0 to 1 mmol/L in the presence of calcimycin resulted (P < .001) in a stimulation of Na+/H+ exchange by 74%. Calcium increased the Vmax for cellular pHi or external Na+ activation of Na+/H+ exchange, whereas it did not affect the Km for H+(i) or external Na+ activation. However, in PKC down-regulated cells, calcium did not activate the Na+/H+ exchange in erythrocytes and the calpain inhibitor E-64d did not prevent this inactivation. Our data show a concomitant increase in free cytosolic Ca2+ concentration and Na+/H+-exchange rate upon protein kinase C activation and a corresponding decrease in both variables upon PKC inhibition, indicating a Ca2+ requirement for protein kinase C activation of Na+/H+ exchange.

Calcium↗
PubMed1998

Proliferation of human peripheral blood mononuclear cells during calcium channel blockade.

To evaluate the role of intracellular calcium and particularly Ca2+ uptake in the initiation of lymphocyte mitogenesis, the effect of mibefradil--which blocks both L- and T-type calcium channels with a more selective blockade of T-type channels--on the proliferation of human peripheral blood mononuclear cells (PBMC) is compared with the effect of nifedipine, which blocks only the L-type calcium channel. The rate of 3H-thymidine, 3H-uridine, and 3H-leucine incorporation into control and concanavalin A-stimulated PBMC in the presence or absence of the calcium channel blockers mibefradil or nifedipine (1, 10, or 50 micromol/L), and of the intracellular calcium antagonist TMB-8 or the calmodulin antagonist W-7 (1, 10, 25, or 50 micromol/L) was assayed in cells cultured for 3 days. The cellular cytotoxicity and the cell number in growing cultures was also determined in mibefradil- or nifedipine-treated control or stimulated cells. Mibefradil and nifedipine reduced the cell number and the 3H-thymidine, 3H-uridine, or 3H-leucine incorporation or the de novo DNA, RNA, or protein synthesis in control and concanavalin A-stimulated human PBMC in a concentration-dependent manner. Mibefradil exhibited a more pronounced inhibition than nifedipine. The inhibitory effect of mibefradil or nifedipine on DNA synthesis was dependent upon the timing of treatment with the drugs. The inhibitory effect of mibefradil or nifedipine on the lymphoproliferative response was nearly abolished if the drugs were added 20 h after cell stimulation. A markedly reduced inhibitory effect was found when mibefradil or nifedipine were added 1 to 7 h after cell stimulation. However, regardless of time of addition, TMB-8 and W-7 caused a persistent inhibition of the proliferation of human PBMC. Our data show that mibefradil had a more pronounced inhibitory effect on the proliferation of human PBMC than nifedipine and that this inhibitory effect on de novo DNA synthesis was dependent upon the timing of treatment with both drugs. Mibefradil and nifedipine also reduce RNA and protein synthesis in human PBMC. Therefore, administration of these calcium channel blockers to inhibit cellular proliferation might be most beneficial at anatomic sites where cellular proliferation is not already an active process, while being ineffective in the presence of ongoing active proliferation, as suggested by some prospective studies.

Adult↗
PubMed1998

Activation by calcium of erythrocyte Na+/H+ exchange in men.

OBJECTIVE: To determine whether protein kinase C is necessary for the calcium activation of the Na+/H+ exchange in human erythrocytes by studying activation by calcium of erythrocyte Na+/H+ exchange in control cells, in protein kinase C-depleted cells after downregulation of protein kinase C with phorbol-12-myristate-13-acetate and in cells that had been treated beforehand with phorbol-12-myristate-13-acetate with and without the calpain inhibitor E-64d. METHODS: Erythrocyte Na+/H+ exchange was measured by determining the initial rates of the influx of Na+ into Na+-depleted, acid loaded cells. The effects of various concentrations (0-1 mmol/l) of CaCl2 and the effects of 1 mmol/l CaCl2 on activation of the intracellular pH and on the external Na+ activation of Na+/H+ exchange were studied. The effects of 1 mmol/l CaCl2 on Na+/H+ exchange in control cells and cells that had been incubated beforehand with and without 1 micromol/l phorbol-12-myristate-13-acetate and with E-64d and 1 micromol/l phorbol-12-myristate-13-acetate for 1, 2, 3 and 24 h were also investigated. RESULTS: Addition of Ca2+ to a concentration in the range 0-1 mmol/l in the presence of calcimycin resulted in stimulation of Na+/H+ exchange: 1 mmol/l CaCl2 increased (P< 0.001) the erythrocyte Na+/H+ exchange by 74%. Calcium increased the maximum rate for activations by intracellular pH and by external Na+ of Na+/H+ exchange, whereas it did not affect the Michaelis-Menten constants for activation by intracellular H+ and external Na+. However, calcium did not activate the Na+/H+ exchange in protein kinase C downregulated erythrocytes and administration of the calpain inhibitor E-64d could not prevent this inactivation. CONCLUSION: Our data indicate that protein kinase C is necessary for the activation by calcium of the erythrocyte Na+/H+ exchange.

Calcium↗
PubMed1998

Human erythrocytes contain Ca2+, calmodulin-dependent cyclic nucleotide phosphodiesterase which is involved in the hydrolysis of cGMP.

To determine whether phosphodiesterase (PDE) is involved in the degradation of cGMP in human erythrocytes, we studied the cell cGMP content in the presence of different PDE inhibitors: zaprinast and dipyridamole, specific inhibitors of cGMP-binding, cGMP-specific PDE (cG-BPDE); vinpocetine, a specific inhibitor of Ca2+, calmodulin-dependent phosphodiesterase (CaM-PDE); an unspecific inhibitor, 3-isobutyl-1-methylxanthine (IBMX). IBMX, zaprinast, and dipyridamole at 30 microM did not affect the intracellular cGMP content. However, vinpocetine at this concentration increased the cGMP content by 102 +/- 14% (p < 0.05). The effect of vinpocetine was dose-dependent, reached the maximal level after 1 min of incubation and flattened at the same level. Ca2+ (10 microM) in the presence of the Ca(2+)-ionophore, A23187 (5 microM), decreased the cGMP content (-23% +/- 4; p < 0.05), which can be explained by the CaM-PDE activation. The Ca(2+)-induced decrease in cGMP was completely inhibited by the CaM antagonist, W-7 (100 microM). These data suggest that erythrocytes contain Ca2+, CaM-PDE.

1-Methyl-3-isobutylxanthine↗
PubMed1997

In vitro proliferative response of human peripheral blood mononuclear cells to concanavalin A.

The proliferation response of human peripheral blood mononuclear cells (PBMC) to concanavalin A (con A) was tested in a medium with or without addition of fetal calf serum (FCS) or a serum substitute. The time profile of the proliferative response of PBMC to con A was different in cells cultured in a medium supplemented with or without FCS. This different pattern occurred for the con A-induced DNA-synthesis as well as for the RNA- or protein-synthesis. The peak proliferation rate and the stimulation index of proliferation of human PBMC to con A was also higher when the cells were cultured in a medium with 10% FCS compared to cells cultured in a FCS-free medium. Substitution of the fetal calf serum by a serum substitute even induced a profound inhibition of the de novo synthesis of DNA in human PBMC. The results indicate that a lymphocyte proliferation response to con A can still be obtained in a culture medium where no FCS was added, although a weaker stimulation occurred in comparison to a culture medium with FCS. However, addition of a serum substitute caused a marked inhibition of the lymphocyte proliferation rate.

Blood Proteins↗
PubMed1997

Cytosolic calcium changes induced by angiotensin II in human peripheral blood mononuclear cells are mediated via angiotensin II subtype 1 receptors.

OBJECTIVE: To determine the effects of angiotensin II (AII) (1-8) on cytosolic free calcium concentrations in the absence and in the presence of the selective angiotensin subtype 1 (AT1) receptor antagonist losartan and of the selective angiotensin subtype 2-receptor antagonist P-186 in human peripheral blood mononuclear cells (PBMC). We also assessed the effect of the AII analogues AII (2-8), AII (3-8) and AII (4-8) on the cytosolic free-calcium concentration in human PBMC. METHODS: The cytosolic free-calcium concentration was assayed in human peripheral blood mononuclear cells by measuring the fluorescence of fura-2 entrapped by these cells. RESULTS: Administration of AII caused a concentration-dependent increase in the cytosolic free-calcium concentration in human peripheral blood mononuclear cells with a half-maximal increase at 5 x 10(-8) mol/l. Also administration of the heptapeptide AII (2-8) increased the intracellular free-calcium concentration in human PBMC, whereas AII (3-8) and AII (4-8) had no effect. The AII (1-8)-induced rise in cytosolic free-calcium concentration was blocked completely by losartan but not by P-186. CONCLUSION: Our data demonstrate that the effects of AII on the cytosolic free-calcium concentration in human PBMC are AT1 receptor-mediated since they were abolished by the specific AII AT1 receptor antagonist losartan but not by the specific angiotensin subtype 2 receptor antagonist P-186.

Angiotensin II↗
PubMed1997

The deletion/insertion polymorphism of the angiotensin converting enzyme gene and cardiovascular-renal risk.

OBJECTIVE: This meta-analysis attempted to derive pooled estimates for the associations between various cardiovascular-renal disorders and the deletion/insertion (D/I) polymorphism of the angiotensin converting enzyme (ACE) gene. METHODS: Case-control studies were combined, using the Mantel-Haenszel approach. Joint P values for continuous variables were calculated by Stouffer's method. Continuous measurements reported in different units were expressed on a percentage scale using the within-study mean of the II genotype as the denominator. RESULTS: The computerized database used for this analysis included 145 reports with an overall sample size of 49 959 subjects. Overall, possession of the D allele was associated with an increased risk of atherosclerotic and renal microvascular complications. In comparison with the II reference group, the excess risk in DD homozygotes (P < 0.001) was 32% for coronary heart disease (CHD; 30 studies), 45% for myocardial infarction (20 studies), 94% for stroke (five studies) and 56% for diabetic nephropathy (11 studies). The corresponding risk in DI heterozygotes amounted to 11% (P= 0.02), 13% (P= 0.02), 22% (P= 0.10) and 40% (P < 0.001), respectively. Hypertension (23 studies), left ventricular hypertrophy (five studies), hypertrophic or dilated cardiomyopathy (eight studies) and diabetic retinopathy (two studies) were not related to the DI polymorphism. Publication bias was observed for CHD, myocardial infarction and microvascular nephropathy, but not hypertension. In studies with DNA amplification in the presence of insertion-specific primers, the risk associated with the DD genotype increased to 150% [95% confidence interval (CI) 76-256; four studies] for diabetic nephropathy, but decreased to 12% (95% CI -3 to 28; seven studies) for CHD and 14% (95% CI -6 to 37; four studies) for myocardial infarction. On the other hand, the pooled odds ratios did not materially change if the meta-analysis was limited to articles published in journals with an impact factor of at least 4. Furthermore, compared with the II control group, the circulating ACE levels (29 studies) were raised 58 and 31% (P < 0.001) in DD and DI subjects, respectively. In contrast, plasma renin (10 studies), systolic and diastolic blood pressure (46 studies) and body mass index (30 studies) were not associated with the D allele. CONCLUSION: The D allele is not associated with hypertension, but behaves as a marker of atherosclerotic cardiovascular complications and diabetic nephropathy. These associations do not necessarily imply a causal relationship and may have been inflated by publication bias. Nevertheless, their possible therapeutic implications may be subject to further investigation in prospective (intervention) studies.

Alleles↗
PubMed1997

Transcranial Doppler velocities in patients with thromboangiitis obliterans.

The idea of cerebrovascular injury in cases of thromboangiitis obliterans was not strange to Leo Buerger, but Jäger (1932), as well Lindenberg and Spatz (1939), first established it. The aim of this study was to investigate the hemodynamics in the basal cerebral arteries by means of transcranial Doppler in patients with thromboangiitis obliterans. Thirty patients (all men; average age 40.03 +/- 16.4 years) were included--one group twenty-four to forty years of age and another group forty-one to fifty years of age. The results show that the blood flow velocities in middle and anterior cerebral arteries in both groups of patients were significantly lower than in healthy persons. The trends towards reduction of blood flow velocity were also evident in posterior cerebral arteries. The authors describe in detail 2 patients who suffered major ischemic stroke. Cerebrovascular disorders in Buerger's disease are probably more frequent than supposed and have to be taken into account.

Adult↗
PubMed1997

Effect of angiotensin-converting enzyme inhibition on Na+/H(+)-exchange and Ca(2+)-efflux in human erythrocytes.

The effect of the angiotensin-converting enzyme inhibitor, captopril, on Na+/H(+)-exchange activity and on Ca(2+)-ATPase mediated Ca(2+)-efflux was investigated in red blood cell membranes of patients with essential hypertension. The erythrocyte Na+/H(+)-exchange rate was measured as the difference in H(+)-efflux rate when measured in the presence or absence of Na+. The erythrocyte Ca(2+)-transport mediated by Ca(2+)-ATPase was assayed as the erythrocyte Ca(2+)-efflux rate. Our data show that captopril, in vitro and in vivo, inhibits the Ca(2+)-ATPase mediated Ca(2+)-efflux rate in human erythrocytes, while in vivo it stimulates the erythrocytes Na+/H(+)-exchange rate.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1996

Cell membrane cation transport systems during aldosterone antagonism.

We conducted a double-blind, placebo-controlled parallel study of the effect of the aldosterone antagonist spironolactone, administered once daily for 1 week to normal male subjects, on blood pressure, intracellular cationic concentrations, and transmembrane cation transport systems and plasma or urinary variables. After a 1-week run-in period on placebo, the subjects (n = 40) were allocated to a placebo or a spironolactone group. Placebo or 100 mg spironolactone was administered once daily in the morning for 1 week. All subjects were investigated at baseline and after 1 week of placebo or spironolactone administration. Standing systolic blood pressure of subjects in the spironolactone group was decreased (p < 0.001) as compared with that of subjects in the placebo group, but standing diastolic blood pressure did not change. Decreased intraerythrocyte and intraplatelet Na+ and free Ca2+ concentration and decreased activity of the platelet Na(+)-pump activity were observed in the spironolactone-treated subjects. The intraerythrocyte and intraplatelet K+ and Mg2+ concentrations, as well as the activities of the erythrocyte Na+, Li(+)-countertransporter and Na+, K(+)-cotransporter, and Na+ and K+ leakage, were not changed during spironolactone administration. The blood pressure-lowering action of spironolactone in men in the standing position is accompanied by a decrease in cytosolic free platelet Ca2+ concentration, by a reduction in intraplatelet and intraerythrocyte Na+ concentration, and in the platelet Na+ pump activity.

Adult↗
PubMed1996

Regulation of human erythrocyte Na+/H+ exchange by soluble and particulate guanylate cyclase.

Guanylate cyclase activity in human erythrocytes is investigated by evaluating the intracellular guanosine 3',5'-cyclic monophosphate (cGMP) content in the presence of various agents that exert specific effects on soluble or particulate guanylate cyclase. The increase in the intraerythrocyte cGMP content by the soluble guanylate cyclase activators nitroprusside and NaNO2 suggests the presence of this enzyme in human erythrocytes. The effects of four different atrial natriuretic peptide (ANP) fragments on the intraerythrocyte cGMP content is also studied. ANP II and ANP III increase the intraerythrocyte cGMP content, whereas ANP I and des-Ser5,des-Ser6-ANP III are ineffective. Thus our data show that human erythrocytes possess particulate guanylate cyclase together with the soluble enzyme. The ANP fragments ANP II and ANP III also activate the erythrocyte Na+/H+ exchange. Nitroprusside, M & B 22948 (an inhibitor of cGMP phosphodiesterase), and the cGMP analogues dibutyryl cGMP and 8-bromoguanosine 3',5'-cyclic monophosphate also increase the erythrocyte Na+/H+ exchange rate. The latter data also suggest that the erythrocyte Na+/H+ exchange is regulated by cGMP.

3',5'-Cyclic-GMP Phosphodiesterases↗