Organic nitrates. II. Synthesis and biological activities of 4-nitrooxymethylphenyl-1,4-dihydropyridines.

Both 2-nitrooxymethyl-4-phenyl- (2) and 4-nitrooxymethylphenyl-1,4-dihydropyridines (3) represent new combinations of two different vasodilating structures. 2 could not be isolated due to its spontaneous lactonization. Derivatives of 3 were obtained via Hantzsch synthesis using nitrooxymethylated benzaldehydes. The inotropic potency in isolated porcine trabecular muscles and the vasodilator activity in isolated porcine coronary arteries of four nitrooxyphenyl-dihydropyridines were determined. Nitrendipine (NTD) and glyceryl trinitrate (GTN) were used for reference. 3 were negative inotropic, however, less than NTD and--except for the dicyano derivative 3d--more than GTN. Vasodilator properties were less pronounced than that of both nitrendipine and GTN. Vascular selectivity was low.

Functional and antiischaemic effects of Monoacetyl-vitexinrhamnoside in different in vitro models.

1. Functional and antiischaemic effects of monoacetyl-vitexinrhamnoside (AVR), a flavonoid with phosphodiesterase (PDE)-inhibitory properties contained in Crataegus species (Hawthorn, Rosaceae) were studied in several in-vitro models. 2. In rabbit isolated femoral artery rings, AVR concentration-dependently reduced developed tension. Vasodilation by AVR was reduced after inhibiting EDRF formation by L-NG-nitro arginine. 3. In spontaneously-beating Langendorff-guinea pig hearts, AVR concentration-dependently enhanced heart-rate, contractility, lusitropy and coronary flow. 4. In isolated electrically-driven Langendorff-rabbit hearts, acute regional ischemia (MI) was induced by coronary artery occlusion and quantified from epicardial NADH-fluorescence photography. AVR (5 x 10(-5) mol/l) induced a slight numerical increase of left ventricular pressure and coronary flow (p > 0.05). MI was reduced (p < 0.05). 5. Monoacetyl-vitexinrhamnoside is an inodilator whose vasodilatory action may be mediated in part by EDRF in addition to PDE-inhibition. Monoacetyl-vitexinrhamnoside does possess marked antiischemic properties even in isolated hearts, suggesting an improvement of myocardial perfusion.

Myocardial effects of flavonoids from Crataegus species.

The influence of the main flavonoids from Crataegus species (hawthorn, Rosaceae) on coronary flow, heart rate and left ventricular pressure as well as on the velocity of contraction and relaxation was investigated in Langendorff perfused isolated guinea pig hearts at a constant pressure of 70 cmH2O. Drug action was evaluated in a concentration range of 10(-7) to 5 x 10(-4) mol/l. An increase of coronary flow caused by the O-glycosides luteolin-7-glucoside (186%), hyperoside (66%) and rutin (66%) as well as an increase of the relaxation velocity (positive lusitropism) by luteolin-7-glucoside (104%), hyperoside (62%) and rutin (73%) were the major effects observed at a maximum concentration of 0.5 mmol/l. Furthermore, slight positive inotropic effects and a rise in heart rate were seen. Similar but less intensive actions were found with the C-glycosides vitexin, vitexin-rhamnoside and monoacetyl-vitexin-rhamnoside. Possible beta-adrenergic activities of the flavonoids could be excluded by the addition of propranolol in fixed concentrations of 10(-8) to 10(-5) mol/l. Moreover, pretreatment of the animals with reserpine (7 mg/kg) did not influence myocardial activity of hyperoside (10(-4) mol/l). As previous experiments showed an inhibition of the 3',5'-cyclic adenosine monophosphate phosphodiesterase, the results suggest an inhibition of this enzyme as the possible underlying mechanism of cardiac action of flavonoids from Crataegus species.

Effects of different inotropes with antioxidant properties on acute regional myocardial ischemia in isolated rabbit hearts.

1. The antiischemic properties of the flavonoids acetylvitexin-rhamnoside (AVR) and luteolin-7-glucoside-(LUT), combining phosphodiesterase (PDE)-inhibitory and antioxidant properties, were studied in comparison to amrinone (AMR) or superoxide dismutase (SOD). The effects of the new dihydropyridine-type calcium-agonist Bay T 5006 were studied in comparison to Bay K 8644. 2. In isolated Langendorff-rabbit hearts perfused at constant pressure, acute regional ischemia (MI) was induced by coronary artery occlusion (CAO) and quantitated from epicardial NADH-fluorescence photography. Drugs were applied either before or after CAO (pre-treatment or treatment) to permit distinguishing the influence of functional and direct cytoprotective actions in the poorly collateralized rabbit hearts. 3. SOD did not affect left ventricular pressure (LVP) or coronary flow (CF) and reduced MI only if applied before CAO. LVP and CF were enhanced by LUT or AMR but not by AVR. MI was reduced to a similar extent in hearts treated with either drug. Cardioprotection by LUT was not improved by starting drug application before CAO. 4. Bay K 8644 reduced LVP and particularly CF, whereas Bay T 5006 did not affect functional parameters. MI was enlarged by Bay K 8644 and remained unaffected by treatment or pretreatment with Bay T 5006. 5. AMR, LUT and AVR possess antiischemic properties related to an improvement of myocardial perfusion. Although oxygen free radicals contribute to ischemic tissue injury, as shown by the cardioprotective effectiveness of SOD, antioxidant properties of the flavonoids LUT and AVR do not seem to be relevant for the antiischemic effects. Our findings also give no evidence for antioxidant properties of dihydropyridines relevant for cardioprotection.

Functional and antiischemic effects of luteolin-7-glucoside in isolated rabbit hearts.

1. The functional effects of the flavonoid luteolin-7-glucoside (LUT) were investigated in Langendorff-rabbit hearts perfused at constant pressure. Repetitive myocardial ischemia was induced by coronary artery ligature and quantified from NADH-fluorescence photography. 2. LUT significantly enhanced left ventricular pressure and the global and relative coronary flow (= global coronary flow/pressure-rate product). 3. LUT significantly diminished epicardial NADH-fluorescence area and intensity. 4. LUT is an inodilator possessing cardioprotective properties. These might be related to an improvement of myocardial perfusion and/or to free radical scavenging properties.

Comparative effects of the dihydropyridine-type calcium-agonists (-)-S-Bay K 8644, (+/-)-Bay-W 5035 and (+/-)-Bay-T 5006 on human platelet aggregability.

1. Human platelet aggregation induced by collagen is concentration-dependently inhibited by dihydropyridine (DHP)-type calcium(Ca)-agonists. 2. There was no significant difference between the maximal anti-aggregatory effects or the anti-aggregatory potencies of (-)-S-Bay-K 8644 (EC50: 5.3 +/- 1.5 x 10(-5) M), (+/-)-Bay-W 5035 (EC50: 14.9 +/- 8.8 x 10(-5) M) or (+/-)-Bay-T 5006 (EC50: 2.7 +/- 1.9 x 10(-5) M) (P > 0.05). 3. Antiaggregatory effects of DHP-type Ca-agonists seem to be independent of Ca-channel activation.

Influence of (-)-S-Bay K 8644, (+/-)-Bay W 5035 and (+/-)-Bay T 5006 on hemodynamics and FITC-dextran 3 elution kinetics in isolated rat hearts.

1. We investigated the effects of the new calcium-agonists (+/-)-Bay W 5035 and (+/-)-Bay T 5006 in comparison to (-)-S-Bay K 8644 on hemodynamics and epimyocardial perfusion in Langendorff rat hearts. 2. At equieffective inotropic concentration, vasoconstriction of coronary resistance vessels was significantly less after (+/-)-Bay W 5035 or (+/-)-Bay T 5006 than after (-)-S-Bay K 8644 application. 3. FITC-Dextran 3 elution kinetics indicated that the epimyocardial vascular volume was significantly reduced only by (-)-S-Bay K 8644. 4. Moreover, (-)-S-Bay K 8644 enhanced transcoronary exchange more markedly than (+/-)-Bay W 5035 or (+/-)-Bay T 5006, reflecting the differences in coronary constrictor activity. 5. We conclude that in comparison to (-)-S-Bay K 8644 the relation between inotropy and vasoconstriction is more favorable for (+/-)-Bay W 5035 or (+/-)-Bay T 5006.

Nitric oxide (EDRF) enhances the vasorelaxing effect of nitrendipine in various isolated arteries.

Recent studies suggest endothelium to be involved in the vasorelaxation of calcium antagonists of the 1,4-dihydropyridine type, which may at least in part be mediated by endothelium-derived relaxing factor (EDRF = NO). To study this effect further, the influence of L-NG-nitro arginine (L-NNA), a specific inhibitor of EDRF-synthesis, on nitrendipine-induced vasorelaxation was examined in different isolated porcine arteries. Coronary, basilary, and tail arteries were bathed in Krebs-Henseleit solution and endothelial function was verified by means of substance P, an EDRF releasing neuropeptide. Vasorelaxation of nitrendipine in PGF2 alpha-precontracted arteries was studied in the presence and absence of L-NNA. Nitrendipine-induced vasorelaxation was markedly reduced by the addition of L-NNA in all vessels studied. Tachyphylactic effects of nitrendipine could be excluded. The obtained results may be explained by an enhancement of nitrendipine action by basally released EDRF, alternatively, by an increased EDRF-release induced by this calcium antagonist. Therefore, in a second series of experiments the release of EDRF was studied in isolated coronary arteries under cumulative application of nitrendipine. Using the nitric oxide scavenging properties of oxyhemoglobin, EDRF release was measured spectrophotometrically by means of methemoglobin formation. The application of nitrendipine resulted in a concentration-dependent increase in the extinction rate, indicating an increased release of NO which could be inhibited by preincubation with L-NNA. It may be concluded that, in functionally intact vessels, vasorelaxation induced by nitrendipine may additionally be mediated by an increased release of EDRF.

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.

Sialic acid removal modulates the myocardial and vascular activity of calcium channel ligands.

Selective removal of sialic acid from isolated guinea pig left atrial strips and rabbit thoracic aortic ring segments was performed by neuraminidase prepared from Clostridium perfringens and was controlled electron microscopically. Preincubation of these organs (2 units/mL; 2 hr) resulted in enzyme mediated hydrolysis of total tissue sialic acid; 55.2% for atria and 60.9% for aorta. Contractile force of atria and arterial diameter of thoracic aorta were measured isometrically and isotonically by means of a force displacement transducer. Pretreatment of both organs with neuraminidase (2 units/mL; 2 hr) in a carbogen saturated organ bath caused a moderate left-hand shift of the cumulative concentration response curves for the dihydropyridine type calcium antagonist nisoldipine, the phenylalkylamine derivative gallopamil and the benzothiazepine diltiazem. EC50 values were significantly lower (P less than 0.05), particularly in the atrial muscle, when compared to untreated preparations. There was no effect of neuraminidase on the negative inotropic and vasodilator potency of the calcium channel modulator fendiline. Conversely, neuraminidase induced a right-hand shift in the concentration response curves shown by the pure calcium agonist (-)-S-Bay K 8644 leading to significantly higher EC50 values in both organs. Similarly, the contractile potency of calcium chloride (atria) and potassium chloride (aorta) was attenuated upon neuraminidase treatment. From the results obtained it is concluded that sialic acid removal may modulate the action of calcium channel ligands through an inhibitory effect on transmembrane calcium fluxes and/or by decreasing the external calcium availability. Whether the present results suggest a functional role for sialic acid in the regulation of calcium channels warrants further investigation.

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.

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)

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.

Vasoactive properties of procyanidins from Hypericum perforatum L. in isolated porcine coronary arteries.

Procanidin fractions (PC) were isolated from Hypericum perforatum L. (Guttiferae). Characterization of the main components of each fraction was performed by UV- and mass spectroscopy. Their biological activity was tested in porcine isolated coronary arteries. All PC fractions antagonized histamine- or prostaglandin F2 alpha-induced arterial contractions. In contrast, vasorelaxation was insignificant in KCl-precontracted coronary arteries except with the higher oligomeric PC fraction 3. Vasoactive properties of the PC seem to be dependent on their relative molecular mass. An inhibition of cellular phosphodiesterase might be involved in the underlying mechanism of action.

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.

Novel halogenated dihydropyridine derivatives with high vascular selectivity.

Calcium channel antagonists of the dihydropyridine type exhibit preferential vasodilator properties. To study whether this vascular selectivity is due to distinct steric modifications or may be influenced by the physicochemical nature of these drugs, contractility in guinea pig heart isolated papillary muscles, vasodilator properties in isolated rabbit femoral arteries and the lipophilicity of some novel halogenated dihydropyridines have been examined. All newly synthesized derivatives exhibited dose-dependent negative inotropic and vasodilator effects. The negative inotropic potency of all the halogenated derivatives was weaker than that of the parent compound nitrendipine. In contrast, compared to nitrendipine the vasodilator potency of the ester substituted derivatives was slightly increased, while halogen substitution in position 2 and 6 of the dihydropyridine nucleus decreased the vasodilator potency. As a result of the different influence on cardiac and vascular smooth muscle an improved vascular selectivity of the drugs was attained. The ester-substituted dihydropyridine derivatives showed a 9 times (3-bromoethyl-nitrendipine) or 11 times (3-chloroethyl-nitrendipine) higher vascular selectivity with respect to nitrendipine. Correlation of the lipophilicity with the physiological properties showed an increase in biological activity with decreasing lipophilicity. Within the ester-halogenated dihydropyridine derivatives an inverse trend was observed (increasing vasodilation with increasing lipophilicity), indicating a different influence of lipophilicity with the ester-substituted compounds on the different tissues examined. The improved vascular selectivity of the novel halogenated dihydropyridines may be at least in part a consequence of the different lipophilicity of the drugs. In addition, differences in the binding affinities of the dihydropyridines subordinate to distinct voltage dependent conformation states of the calcium channel may contribute.

Lipophilicity and pharmacodynamics of cardiotonic steroids in guinea-pig isolated heart muscle preparations.

1. The inhibitory potency of cardiotonic steroids on myocardial Na+-K+-ATPase increases with increasing lipophilicity. Employing the inotropic action on guinea-pig isolated left atria, the relationship between lipophilicity, chemical structure and the pharmacodynamic properties of cardiac glycosides was further examined. Nineteen digitoxigenin- and digoxigenin-derivatives, whose lipophilic nature and inhibitory effects on the myocardial Na+-K+-ATPase have been previously investigated, were tested. 2. All steroids exhibited positive inotropic effects which varied with the lipophilicity of these drugs. The dependence of the relationship between these two parameters on structural transformations of the steroids showed qualitatively very close parallelism to that between lipophilicity and their inhibitory effects on myocardial Na+-K+-ATPase. 3. The positive inotropic effects and the inhibitory effects on myocardial Na+-K+-ATPase also correlated very well, exhibiting similar patterns in their respective correlations with the individual lipophilicity parameters. 4. It is inferred that (a) the positive inotropic effects of the cardiac glycosides vary with their lipophilicity, exhibiting trends similar to those shown for their inhibitory effects on myocardial Na+-K+-ATPase, (b) this interdependence is secondary to the influence of structural changes, particularly on the steroid nucleus, and (c) both the lipophilic nature and pharmacodynamic behaviour of the cardiac glycosides almost exclusively depend on the steroid nucleus itself.

Influence of derivation on the lipophilicity and inhibitory actions of cardiac glycosides on myocardial Na+-K+-ATPase.

Lipophilicity and inhibitory actions on guinea-pig heart Na+-K+-ATPase of twenty-six digitalis and six strophanthus glycosides comprising the aglycones, mono-, bis-, tris-sugar, alkylated (acylated) tris-sugar, acyl steroid derivatives and three cardanolides were investigated. Their octanol/water partition coefficients (P), reversed phase thin layer (r.t.l.c.) and reversed phase high performance liquid chromatography (r.h.p.l.c.) were determined and the viability of these methods as a measure of the lipophilicity of the cardiotonic steroids evaluated. The influence of lipophilicity and so also structural changes on the inhibitory effects of the cardiac glycosides on myocardial Na+-K+-ATPase was then examined. It is concluded that (a) r.t.l.c. and r.h.p.l.c. are just as effective as the conventional shake-flask method for estimation of the lipophilicity of cardiac glycosides and (b) the inhibitory potencies of cardiotonic steroids on the myocardial Na+-K+-ATPase increase with growing lipophilicity. The relationship between these two parameters is, however, governed by the influence of substitution or derivation of structural components on their inhibitory potencies on the myocardial Na+-K+-ATPase.