Biomedical subjects

G Kojda

Publications and source records attributed to G Kojda.

51 records · Page 3Linked to original sources

PubMed1996

Low increase in cGMP induced by organic nitrates and nitrovasodilators improves contractile response of rat ventricular myocytes.

Whether organic nitrates are bioactivated to NO in cardiac muscle cells and may thus directly affect cardiac contractile function has remained an open question. Therefore, we determined the effects of the organic nitrates glyceryl trinitrate (100 mumol/L), pentaerythritol tetranitrate (10 mumol/L), and isosorbide-5-mononitrate on electrically stimulated contractile response (CR) and cAMP and cGMP content of isolated adult rat ventricular cardiomyocytes compared with different concentrations of the spontaneous NO donors S-nitroso-N-acetyl-d,1-penicillamine (SNAP) and 2,2-diethyl-1-hydroxy-1-nitroso-hydrazine (DEA/NO). A high concentration of spontaneous NO donors (100 mumol/L caused a large increase in cGMP content that was accompanied by a decrease in CR to 73.8 +/- 6.7% (SNAP) and 80.9 +/- 6.1% (DEA/NO) of the control values. Inhibition of cGMP-dependent protein kinase by 10 mumol/L KT 5822 converted this effect into a pronounced improvement of CR (163.5 +/- 14.0%) By contrast, the organic nitrates caused a small but significant increase in cGMP, which was accompanied by an increase in cAMP and CR identical to that induced by 10 nmol/L isoprenaline (141.6 +/- 6.4%) A similar effect was observed with a low concentration (1 mumol/L of SNAP and DEA/NO. All increases in CR induce by nitrates were abolished after inhibition of cAMP-dependent protein kinase by Rp-cAMPS (10 mumol/L). The positive contractile effect of isoprenaline was enhanced by 1 mumol/L SNAP. This effect was also demonstrated in isolated rat papillary muscles. These results indicate that in cardiac muscle (1) organic nitrate are bioactivated to NO; (2) this results in a moderate increase in cGMP, which causes an improved CR by increasing cAMP and activating cAMP-dependent protein kinase; and (3) a large increase in cGMP, produced by high doses of NO donors, reduces CR because of the activation of CGMP-dependent protein kinase.

Animals↗

PubMed1996

Demonstration of NADPH-diaphorase (NO-synthase) in sebaceous glands of the mammalian integument, with remarks on the glandular capillary net.

The study demonstrates weakly to strongly positive reaction staining for NADPH-diaphorase/NO- synthase in the peripheral cells of sebaceous glands in the hairy skin of domesticated mammals. Additionally, the structure of the blood capillary system surrounding these glands is better elucidated. The results obtained are discussed in view of a modulatory action of NO generated by these enzyme activities, implying a direct influence of this substance on the contractile elements of gland-associated blood capillaries. In this way, a simple and self-regulatory mechanism to couple blood flow and glandular metabolism can be proposed.

Animals↗

PubMed1995

The new NO donor SPM3672 increases cGMP and improves contraction in rat cardiomyocytes and isolated heart.

Recent evidence indicates that organic nitrate esters may directly affect heart muscle. In the present study we investigated the effects of the new organic nitrate ester, N-(3-nitratopivaloyl)-1-cysteineethylester (SPM3672), on isolated adult rat ventricular myocytes and on Langendorff preparations of spontaneously beating rat hearts perfused in a volume-constant manner. In cardiomyocytes SPM3672 (100 microM) induced a significant increase in the basal level of cGMP to 232 +/- 44% (n=8) indicating its metabolism to nitric oxide. This was associated with an enhanced contractile response to electrical field stimulation (to 174 +/- 9%, n=108). In isolated hearts SPM3672 elicited a slight reduction of coronary perfusion pressure (-15 +/- 8%) and a significant increase in maximal left ventricular pressure (LVPmax), dp/dtmax and dp/dtmin amounting to 18 +/- 7%, 18 +/- 6% and 21 +/- 7% (n=7), respectively. Oxygen consumption and heart rate remained constant. Thus, SPM3672 improved the contractile response of cardiomyocytes and of isolated heart. This is probably due to the metabolism of SPM3672 to nitric oxide in ventricular cardiomyocytes.

Animals↗

PubMed1995

Comparison of the vasorelaxing effect of different nitrovasodilators in conductive arterial and venous blood vessels.

We tested classically used organic nitrovasodilators such as s-nitroso-n-acetyl-D,L-penicillamine, 3-morpholino-sydnonimine, pentaerythrityl-tetranitrate, isosorbide-dinitrate, isosorbide-mononitrate, glyceryl-trinitrate on different isolated conductive arterial and venous blood vessels of the same species (rabbit). We found an up to two orders of magnitude more pronounced venoselectivety in the systemic-circulation as compared to the lung-circulation. ISMN and PETN were most venoselective nitrovasodilators, with PETN being the most potent drug in all vessels studied.

Animals↗

PubMed1995

Effects of pentaerythrityl-tetranitrate and isosorbide-5-mononitrate in experimental atherosclerosis.

This study was performed to determine whether long-term treatment with organic nitrovasodilators exhibit pharmacological effects on the development of atherosclerotic lesions and endothelial dysfunction in the cholesterol fed rabbit. The major finding of this study is that PETN, but not ISMN, decreases the extent of aortic intimal lesions and the development of endothelial dysfunction. In addition, 15 weeks of feeding a diet enriched with either PETN or ISMN did not induce a measurable extent of vascular in-vitro tolerance to the vasodilator activity of these drugs.

Animals↗

PubMed1995

In vivo effects of pentaerythrityl-tetranitrate and isosorbide-5-mononitrate on the development of atherosclerosis and endothelial dysfunction in cholesterol-fed rabbits.

We wished to determine whether long-term treatment with organic nitrovasodilators has pharmacological effects on the development of atherosclerotic lesions and endothelial dysfunction in cholesterol-fed rabbits. For 15 weeks, six groups of 9 New Zealand White rabbits received a standard diet, which contained no admixture, pentaerythrityl-tetranitrate (PETN 6 mg/kg body weight/day), or isosorbide-5-mononitrate (ISMN 2 mg/kg body weight/day). In the other three groups, the same diets were further enriched with cholesterol (0,75%). Four rings of thoracic aorta were used for tension studies; these rings and the aortas from the aortic arch to bifurcation were then fixed in formol and stained with Sudan IV to determine the area of luminal atherosclerotic lesions by a computerized laser-scanning approach. The cholesterol diet increased plasma levels of cholesterol from 69.8 +/- 10.4 to 907.1 +/- 85.5 mg/dl. A similar result was obtained in the group receiving PETN/cholesterol, but the group fed ISMN/cholesterol showed a significantly higher plasma level of cholesterol (1,165 +/- 81.4 mg/dl). Plasma levels of PETN metabolites were still detectable by gas chromatography/mass spectrometry after a 24-h in vivo washout period. The cholesterol diet induced a pronounced degree of atherosclerotic lesions in the aortic arch and the thoracic and abdominal aorta: 73.3 +/- 1.9, 46.3 +/- 2.5, and 49.6 +/- 3.6%, respectively. Additional treatment with PETN resulted in a reduction of this atherosclerotic area to 58.6 +/- 2.05% (p < 0.0001), 34.7 +/- 1.98% (p < 0.01), and 39.3 +/- 3.06% (p < 0.05). In contrast, ISMN had no significant effect on this parameter. The cholesterol diet also induced an endothelial dysfunction as indicated by the diminished vasorelaxation induced by acetylcholine (ACh). Treatment with PETN completely inhibited the development of endothelial dysfunction, whereas ISMN had no effect. In the three groups receiving a cholesterol diet, an increased extent of aortic lesions significantly correlated with increased endothelial dysfunction measured in the same preparations. The long-term treatment with PETN did not affect the vasorelaxing potency of PETN in aortic rings, and similar results were obtained in the case of ISMN. We conclude that long-term treatment with doses of PETN, which do not promote the development of in vitro vascular nitrate tolerance, may protect against atherosclerosis and endothelial dysfunction. This novel, yet unknown pharmacodynamic quality of nitrovasodilators like PETN may contribute to their long-term efficacy in coronary artery disease but may also imply new therapeutic indications in the future.

Acetylcholine↗

PubMed1994

Nitrovasodilator-induced relaxation and tolerance development in porcine vena cordis magna: dependence on intact endothelium.

1. Isolated segments of porcine vena cordis magna exhibited a reproducible contractile activity upon application of prostaglandin F2 alpha (PGF2 alpha) or KCl, that was independent of the presence of intact endothelium. Substance P (3 nM) elicited strictly endothelium-dependent relaxations amounting to 46.1 +/- 1.4% (n = 206) of contractions induced by 10 microM PGF2 alpha. 2. S-nitroso-N-acetyl-D,L-penicillamine (SNAP), a compound that spontaneously liberates nitric oxide, concentration-dependently relaxed PGF2 alpha-precontracted (50 microM) venous segments. Tolerance induction (incubation with 100 microM SNAP for 30 min) within the same segments resulted in a 3 fold attenuation of this effect, which was not further reduced after additional preincubation with glyceryl trinitrate (GTN). Removal of endothelium or the presence of N omega-nitro-L-arginine methylester (L-NAME) significantly improved the potency of SNAP before and after tolerance induction. 3. Concentration-dependent relaxations induced by GTN in non-tolerant veins were similar in the presence and absence of endothelium but much more reduced in tolerant endothelium-denuded (75 fold) compared to intact (20 fold) segments. In contrast, the presence of L-NAME significantly improved GTN-activity solely in non-tolerant veins, which, therefore, also resulted in a more pronounced attenuation of activity due to tolerance induction (100 fold). Preincubation of intact veins with SNAP also reduced GTN-activity but to a lesser extent (10 fold). 4. The more delayed but much longer, and compared to GTN somewhat weaker, acting new nitrovasodilator N-(3-nitrato-pivaloyl)-1-cysteineethylester (SPM 3672) was more potent in denuded than intact non-tolerant venous segments. Induction of tolerance by GTN resulted in a 2 fold-attenuation of potency. This effect was increased to 15 fold in denuded veins but solely due to enhanced potency of SPM 3672 caused by removal of endothelium.5. These data demonstrate that intact endothelium of porcine vena cordis magna attenuates the relaxant potency of nitrovasodilators but also probably participates in vascular bioactivation of GTN.We suggest that the reduced potency of nitrovasodilators is due to endogenous production of nitricoxide, which may affect the soluble guanylate cyclase/cyclic GMP-system or inhibit nitrate bioactivation pathways.

Animals↗

PubMed1994

Demonstration of NADPH-diaphorase (NO-synthase) in the apocrine and eccrine skin glands of domesticated mammals.

The study demonstrates a strong enzyme histochemical and immunohistochemical reaction staining for NADPH-diaphorase/NO-synthase in the secretory cells of the apocrine glands in the hairy skin, and the eccrine glands in the foot pads of domesticated mammals. The results obtained are discussed in view of a regulatory action of the NO generated by these enzyme activities, implying a direct influence of NO on the contractile properties of glandular myoepithelial cells. In this way, a basic and simple mechanism to couple secretion production and secretion extrusion can be proposed.

Animals↗

PubMed1993

Influence of endothelium and nitrovasodilators on free thiols and disulfides in porcine coronary smooth muscle.

It is hypothesised that the well known development of tolerance to the vasodilating action of organic nitrates is contributed by intracellular depletion of free thiols occurring during repeated treatment with these drugs. Therefore, ring segments of porcine coronary arteries with and without endothelium were treated for 30 min with either vehicle or 100 microM of isosorbide-5-mononitrate, glyceryl trinitrate, S-nitroso-N-acetyl-D,L-penicillamine or N-(3-nitratopivaloyl)-1-cysteine-ethylester (SPM 3672), and the content of histochemically stained free thiols (-SH) and disulfides (S-S-) was measured densitometrically in single smooth muscle cells. In the presence of endothelium the content of -SH in smooth muscle cells of controls (n = 8) gave an extinction of 0.127 +/- 0.013 in the intima and 0.120 +/- 0.010 in the media. The corresponding values for S-S- were 0.684 +/- 0.084 and 0.535 +/- 0.120 (n = 8). Removal of endothelium reduced S-S- to 82.1 +/- 70% and increased -SH to 126.7 +/- 6.7%. Treatment with all nitrates reduced -SH in intact artery segments to a similar degree, ranging between 54.0 +/- 4.4 and 68.7 +/- 4.7% (n = 8-10). In contrast, S-S- content was less affected and reached values between 70.6 +/- 2.8 and 91.6 +/- 6.0% (n = 8-9). As evaluated by tension studies, tolerance developed for glycerol trinitrate and isosorbide-5-mononitrate but not for S-nitroso-N-acetyl-D,L-penicillamine. Induction of tolerance with glycerol trinitrate (0.1 mM) produced a significantly more pronounced attenuation in activity of isosorbide-5-mononitrate than tolerance induction with isosorbide-5-mononitrate (1 mM). In contrast, the potency of SPM 3672 was not reduced in glycerol trinitrate-tolerant arteries. We conclude that, in porcine coronary arteries, an intact endothelium modifies intracellular thiols and disulfides. In addition, nitrate tolerance is associated with, but probably not caused by, thiol depletion.

Analysis of Variance↗

PubMed1993

Nitric oxide liberating, soluble guanylate cyclase stimulating and vasorelaxing properties of the new nitrate-compound SPM 3672.

Development of tolerance as a consequence of organic nitrate therapy such as that which occurs with glyceryl trinitrate (GTN) appears to be associated with a depletion of free thiols in vascular smooth muscle. In this study, we investigated N-[3-nitratopivaloyl]-L-cysteineethylester (SPM 3672), a new compound containing a nitrate and a thiol moiety, in direct comparison with GTN. Liberation of nitric oxide (NO) from GTN and SPM 3672 measured in vitro was rather low and was markedly potentiated by addition of cysteine only in the case of GTN. Pronounced activation of a partially purified human soluble guanylate cyclase (sGC) by GTN was observed only after addition of cysteine, whereas a comparative activation by SPM 3672 occurred with and without addition of this thiol. In contrast, SPM 4946 (N(-)[3-hydroxypivaloyl]-L-cysteineethylester), a derivative of SPM 3672 lacking the nitrate-ester moiety, did not activate sGC. Activation of sGC by GTN and SPM 3672 was nearly abolished by oxyhemoglobin. Incubation of isolated porcine coronary artery rings with GTN or SPM 3672 resulted in a similar increase in vascular cyclic GMP levels. In rat aorta, GTN was a more potent vasorelaxant than SPM 3672 and produced a greater degree of tolerance. Vasorelaxation induced by GTN occurred with rapid onset and was brief, whereas SPM 3672 produced long-lasting relaxation with a more delayed onset. This kinetic pattern was confirmed in porcine coronary arteries, in which both nitrates exhibited marked relaxation, with GTN being slightly more potent than SPM 3672.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Intervascular and stimulus selectivity of nitrendipine and related derivatives in KCl and prostaglandin F2 alpha precontracted porcine arteries.

1. Dihydropyridine-type calcium entry blockers exhibit a different vasodilator potency depending on the arterial tissue (intervascular selectivity) as well as on the precontracting stimulus used (stimulus selectivity). In addition, the structure of their ester side chains seems to influence their activity. 2. Vascular activity of nitrendipine and six related 3-ester side chain derivatives was investigated in isolated coronary, ulnar and basilar arteries of the pig following precontraction with KCl or prostaglandin F2 alpha (PGF2 alpha). 3. After depolarization, all dihydropyridines exhibited a weak preferential action on coronary arteries. Bay E 6927 produced the strongest effect in all vessel types. By contrast, precontraction with PGF2 alpha resulted in a marked preferential action in basilar arteries, although higher concentrations of the dihydropyridines were required for half maximal vasorelaxation. In each case, ulnar arteries were less sensitive. 4. Except with Bay O 5572, the most bulky substituted and least active derivative, only moderate differences were observed within the dihydropyridines studied. On the other hand, there was a pronounced increase in the ratios of the half maximal active concentrations required after precontraction of the vessels with PGF2 alpha compared to KCl (stimulus selectivity) following a limited prolongation of the 3-ester side chain up to an isopropyl-group. 5. It is suggested that the observed shift in the intervascular selectivity after precontraction with PGF2 alpha is a consequence of different contractile mechanisms in the three vessel types studied. The degree of the stimulus selectivity may also depend on the structure of the dihydropyridines.

Animals↗

PubMed1991

The influence of 3-ester side chain variation on the cardiovascular profile of nitrendipine in porcine isolated trabeculae and coronary arteries.

It has been reported that the lipophilicity of dihydropyridine-type calcium entry blockers may influence both their negative inotropic and their vasodilator activities. The action of nitrendipine and six related 3-ester side-chain derivatives with increasing alkyl and aryl substituents have been investigated in isolated porcine trabecular muscles and coronary artery rings. The lipophilicity of the drugs was determined by high-pressure liquid chromatography. In addition, some sterical parameters of the ester derivatives were considered. For the drugs tested, an increase in 3-ester side chain volume correlated well with increasing lipophilicity. Compared to nitrendipine, vascular selectivity of the ester side-chain derivatives, as expressed by the ratio of their negative inotropic and vasodilator activities, was much reduced. Neither vasodilator nor negative inotropic activity was directly related to the corresponding lipophilicity. Based on these results, earlier suggestions about the influence of the ester side-chain in dihydropyridines on their cardiovascular profile are extended.

Animals↗

PubMed1991

Hydrophobic properties of novel dihydronaphthyridine calcium antagonists and biological activity in porcine isolated cardiac and vascular smooth muscle.

Dihydronaphthyridine calcium antagonists are structurally related to the well known dihydropyridines and act in a similar manner. In order to establish the vascular selectivity of these compounds contractile force was evaluated in porcine isolated ventricular trabeculae and right coronary arteries. The dihydropyridine derivatives nisoldipine and nitrendipine as well as the structurally different compounds gallopamil and flunarizine were included for comparison purpose. All compounds studied exhibited dose-dependent negative inotropic and vasodilator activities. The negative inotropic potency of all dihydronaphthyridines, especially of the highly lipophilic bulky ester-variated derivatives (Goe 5584-A, Goe 5806-A) was comparable to that of flunarizine but was considerably less pronounced than that of nisoldipine, nitrendipine or gallopamil. By contrast, half-maximal vasodilator responses of the dihydronaphthyridines studied in coronary arteries being in the nanomolar concentration range were comparable to the dihydropyridines nisoldipine and nitrendipine, whereas the activity of gallopamil and flunarizine was less marked. On the other side the dihydronaphthyridines, especially the more hydrophilic 3-ethylester-4-(2-cyanophenyl) derivative Goe 5606, exerted an obvious biphasic concentration-response behaviour in coronary arteries leading to a high affinity relaxant process in subnanomolar concentrations, whereas the low affinity response could be observed at rather high concentrations (mostly greater than 1 microM). Mainly due to their relative uneffectiveness in cardiac muscle, vascular selectivity of the dihydronaphthyridines was considerably higher than that of the structurally related dihydropyridines nisoldipine resp. nitrendipine increasing in the following order: nitrendipine less than nisoldipine less than Goe 5606 less than Goe 5438 less than Goe 5584-A less than Goe 5806-A. By contrast, gallopamil exerted a slight cardiac preference, whereas the vascular selectivity of flunarizine was also pronounced.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Reduced responses of nitrendipine in PGF2 alpha-precontracted porcine isolated arteries after pretreatment with methylene blue.

Vascular activity of nitrendipine (NTD) in different depolarized and prostaglandin F2 alpha (PGF2 alpha)-precontracted isolated porcine arteries was examined in the presence and absence of methylene blue (MB). Presence of MB potentiated the PGF2 alpha-induced contractions in all vessels studied and reduced the response of NTD in coronary and basilar arteries seven- to 23-fold. Only in ulnar arteries was the affinity of NTD slightly increased. In contrast, MB did not modify the affinity of papaverine under these conditions. Furthermore, MB had no influence on KCl-induced contractions and subsequent vasorelaxation by NTD. It is proposed that MB impaired endothelium derived relaxing factor, thereby stimulating and/or increasing the calcium influx through receptor-operated calcium channels.

Animals↗

PubMedDate not supplied

The influence of endothelium on the action of PGF2 alpha and some dihydropyridine-type calcium antagonists in porcine basilar arteries.

Vascular endothelium modulates the effect of various vasoconstricting mediators as well as the affinity of dihydropyridine-type calcium entry blockers. To further investigate this influence, vasoconstriction by PGF2 alpha as opposed to KCl and the affinity of nitrendipine and some related 3-ester side-chain derivatives were determined in isolated porcine basilar arteries in the presence and in the absence of intact endothelium, as well as in the presence of methylene blue. Treatment with methylene blue or mechanical endothelial damage increased the contractile work of basilar arteries stimulated by PGF2 alpha and reduced the affinity of the dihydropyridines in such precontracted vessels. Both experimental conditions resulted in nearly the same effect. In addition, the degree of intact endothelium, as determined by substance-P-induced vasodilation, significantly correlated with the corresponding efficacy of all dihydropyridines examined. In contrast, KCl-mediated contractions remained unchanged. It is suggested that the endothelium (probably due to the production and release of endothelium-derived vasorelaxing factors, such as EDRF and/or prostacyclin) may attenuate PGF2 alpha-induced transmembrane calcium influx through receptor operated calcium channels, whereas potential operated calcium channels seems to be unaffected.

Animals↗