Pharmacological effects of an aldehyde type alpha/beta-adrenoceptor blocking agent with vasodilating properties

Influence of dose and route of administration on the enantioselective pharmacokinetics of TJ0711 hydrochloride in rats

The enantioselective pharmacokinetics of TJ0711 hydrochloride were studied in rats given different doses of rac-TJ0711 hydrochloride via intravenous and oral routes. R- and S-TJ0711 hydrochloride were both rapidly absorbed, and the average AUC0-∞ of R-TJ0711 hydrochloride was greater than that of S-TJ0711 hydrochloride after intragastric administration, with an R/S AUC ratio 1.11 and 1.35 for 30 and 50 mg/kg dose group, respectively. In contrast, the average AUC0-∞ of R-TJ0711 hydrochloride was smaller than that of S-TJ0711 hydrochloride after intravenous injection, with an R/S AUC ratio 0.57 and 0.73 for 10 and 20 mg/kg dose group, respectively. R-TJ0711 hydrochloride plasma half-lives were shorter than those of S-TJ0711 hydrochloride for all groups. AUC0-4h and Cmax between the two enantiomers were significantly different after oral administration of 50 mg/kg dose of the racemate, while no significant differences between the two enantiomers were found for all the pharmacokinetic parameters of the 30 mg/kg dose group. Significant differences between the two enantiomers were detected for nearly all the pharmacokinetic parameters after intravenous administration, except for the VZ of 20 mg/kg dose group. This study suggests that dose and route of administration will influence the enantioselectivity in the pharmacokinetics of TJ0711 hydrochloride in rats.

β-adrenoreceptor blocking and antihypertensive activity of PP-24, a newly synthesized aryloxypropanolamine derivative

PP-24 is a newly synthesized putative β-adrenoceptor antagonist. The objective of the study was to the evaluate β-adrenoceptor blocking activity of PP-24 on isolated rat preparations: right atria, uterus and colon. Effects on the rat ECG and renal hypertension (induced by left renal artery ligation) were also investigated. Treatment with PP-24 (3 and 10 mg kg−1) for 7 days in rats with renal hypertension significantly reduced the mean atrial blood pressure. Single i.v. injections of isoprenaline (0.3, 1 and 3 μg kg−1) alone in normal anaesthetized rat caused hypotension and tachycardia, while PP-24 alone produced dose-dependent falls in mean aterial pressure and bradycardia. Pretreatment of anaesthetized rats with test compounds significantly blocked the hypotension response but not the tachycardia induced by isoprenaline (0.3, 1 and 3 μg kg−1). The pA2 of PP-24 to β1-, β2- and β3-adrenoceptors was 7.72 ± 0.082, 7.40 ± 0.082 and 6.39 ± 0.16, respectively. The β1/β2 selectivity ratio was 2.08, compared with 1.27 for propranolol and 39.17 for atenolol. It is concluded that PP-24 possesses β-adrenoceptor blockade activity but with non-specific affinity for β1- and β2-adrenoceptor subtypes. The rank order of potency of the antagonists for β1-adrenoceptors was atenolol > PP-24 > propranolol. The antihypertensive activity of PP-24 in rats with renal hypertension appears to be due to blockade of β-adrenoceptors.

Selective β1-adrenoreceptor blocking activity of newly synthesized acyl amino-substituted aryloxypropanolamine derivatives, DPJ 955 and DPJ 890, in rats

The in-vivo β-adrenoreceptor antagonistic activity of test compounds DPJ 955 and DPJ 890 was assessed against β-adrenoreceptor agonist (isoprenaline) induced tachycardia in anaesthetized rats. The selectivity to block isoprenaline responses on different β-adrenoreceptor subtypes (β1, β2 and β3) of the test compounds was carried out on isolated rat right atria, isolated rat uterus and isolated rat colon preparations, respectively. Intravenous injection of isoprenaline alone in anaesthetized rats caused hypotension and tachycardia. DPJ 955 or DPJ 890 alone produced a fall in mean arterial pressure and bradycardia in a dose-dependent manner. Administration of isoprenaline to anaesthetized rats pre-treated with test compounds significantly blocked both the tachycardial and hypotensive responses induced by isoprenaline. The test compounds shifted the concentration response curves of isoprenaline towards the right for isolated rat right atrial preparations, rat uterus and rat colon, indicating β1, β2 and β3 adrenoreceptor blockade, respectively. The selectivity ratio for β1/β-adrenoreceptors to DPJ 955 and DPJ 890 was 64.6 and 83.2, respectively. DPJ 890 was more potent in blocking β1-adrenoreceptors and was more selective towards β1 receptors than to other β-adrenoreceptor subtypes. In conclusion, DPJ 955 and DPJ890 have β-adrenoreceptor blocking activity with high selectivity for the β1-adrenoreceptor subtype.

β-Blocking activity of PP-34, a newly synthesized aryloxypropanolamine derivative, and its cardioprotective effect against ischaemia/reperfusion injury in laboratory animals

β-Adrenoceptor antagonists are widely used in cardiovascular medicine. However, the main side effect of these drugs is due to antagonism of β2-adrenoceptors in the airways, resulting in broncho-spasm. Therefore, more cardioselective β-blockers have been developed to offer a lower side effect profile. We have studied a new aryloxypropanolamine derivative (PP-34) with more cardioselectivity and efficacy against ischaemia/reperfusion injury in rats. Oxalate salts of 1-(tert-butylamino)-3-(5-tert-butylaminomethyl-2-methoxyphenoxy) propan-2-ol (PP-34) is a novel β-adrenoceptor antagonist. In-vitro studies in rat isolated right atria, guinea-pig trachea and rat distal colon preparations were carried out to investigate the potency of PP-34 towards different β-adrenoceptor subtypes. pA2/pKB values of PP-34 for β1, β2, and β3 adrenoceptor were 7.89 ± 0.15, 6.13 ± 0.09 and 6.30 ± 0.19, respectively. The β1/β2 selectivity ratio calculated was in the order of PP-34 > atenolol > propranolol. Pre-ischaemic administration (20 min before coronary occlusion) of PP-34 (0.3 or 1 mg kg−1) showed cardioprotective effects against ischaemia/reperfusion injury in rats and significantly reduced arrhythmias, infarct area and necrosis induced by ischaemia/reperfusion injury. The efficacy of PP-34 was found to be greater then atenolol. In conclusion, PP-34 is a cardioselective β-adrenoceptor antagonist, possessing potent anti-arrhythmic and cardioprotective effects against ischaemia/reperfusion injury in rats.

Pharmacokinetic-pharmacodynamic modelling of S(-)-atenolol in rats: reduction of isoprenaline-induced tachycardia as a continuous pharmacodynamic endpoint

BACKGROUND AND PURPOSE

For development of mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) models, continuous recording of drug effects is essential. We therefore explored the use of isoprenaline in the continuous measurement of the cardiovascular effects of antagonists of beta-adrenoceptors (beta-blockers). The aim was to validate heart rate as a pharmacodynamic endpoint under continuous isoprenaline-induced tachycardia by means of PK-PD modelling of S(-)-atenolol.

EXPERIMENTAL APPROACH

Groups of WKY rats received a 15 min i.v. infusion of 5 mg kg(-1) S(-)-atenolol, with or without i.v. infusion of 5 microg kg(-1) h(-1) isoprenaline. Heart rate was continuously monitored and blood samples were taken.

KEY RESULTS

A three-compartment model best described the pharmacokinetics of S(-)-atenolol. The PK-PD relationship was described by a sigmoid Emax model and an effect compartment was used to resolve the observed hysteresis. In the group without isoprenaline, the variability in heart rate (30 b.p.m.) approximated the maximal effect (Emax=43+/-18 b.p.m.), leaving the parameter estimate of potency (EC50=28+/-27 ng ml(-1)) unreliable. Both precise and reliable parameter estimates were obtained during isoprenaline-induced tachycardia: 517+/-13 b.p.m. (E0), 168+/-15 b.p.m. (Emax), 49+/-14 ng ml(-1) (EC50), 0.042+/-0.012 min(-1) (k(eo)) and 0.95+/-0.34 (n).

CONCLUSIONS AND IMPLICATIONS

Reduction of heart rate during isoprenaline-induced tachycardia is a reliable pharmacodynamic endpoint for beta-blockers in vivo in rats. Consequently this experimental approach will be used to investigate the relationship between drug characteristics and in vivo effects of different beta-blockers.

Study of β-Adrenoreceptor Antagonistic Activity of DPJ 904 in Rats

beta-Adrenoreceptor antagonistic activity of a newly synthesized compound was evaluated in vivo by measuring the mean arterial blood pressure and heart rate of urethane-anesthetized rats treated with isoprenaline. In vitro beta(1)-, beta(2)- and beta(3)-antagonism was studied using isolated rat right atria, isolated rat uterus and isolated rat colon preparations, respectively, in comparison to isoprenaline response. DPJ 904 (1, 3 and 10 mg/kg, i.v.) produced dose-dependent hypotensive and bradycardia response in anesthetized rat. DPJ 904 (1, 3 and 10 mg/kg, i.v.) significantly inhibited both the tachycardial effects and hypotensive response induced by isoprenaline. DPJ 904-antagonized isoprenaline induced positive chronotropic effects of isolated rat right atria and a uterine relaxant effect indicating beta(1)- and beta(2)-blockade. The parallel shift to the right of the concentration-response curve of isoprenaline in the presence of DPJ 904 in KCl (30 mmol/l) induced contraction of the rat colon suggesting that DPJ 904 also possessed beta(3)-adrenoreceptor antagonistic activity. The selectivity to beta(1)-adrenoreceptor was nearly 20.5 times greater than to beta(2)-adrenoreceptor. The present study indicates that DPJ 904 possesses beta-adrenoreceptor antagonistic activity with slightly more affinity to the beta(1)-adrenoreceptor subtype.

Anti-Hypertension Effect of Vanylidilol: A Phenylaldehyde α/β-Adrenoceptor Blocker with Endothelium-Dependent and K+ Channels Opening-Associated Vasorelaxant Activities

The antihypertensive effect of vanylidilol, a new alpha/beta-adrenoceptor antagonist with endothelium-dependent and K(+)-channel-opening activities, was investigated in normotensive and hypertensive Wistar rats. Vanylidilol competitively antagonized (-)isoproterenol-induced positive chronotropic effects, inotropic effects, and tracheal relaxation effects in isolated rat right atria, left atria, and guinea pig tracheal strips in a concentration-dependent manner. Vanylidilol's apparent pA(2) values were 6.36 +/- 0.08 (right atria), 6.41 +/- 0.07 (left atria), and 6.31 +/- 0.06 (trachea). Vanylidilol also produced a competitive antagonism of phenylephrine-induced contraction in the isolated rat aorta with pA(2) values of 6.79 +/- 0.18. In the radioligand binding assay, vanylidilol inhibited [(3)H]CGP-12177 binding to rat ventricle and lung tissues and [(3)H]prazosin binding to brain membranes with Ki values of 535.17, 2,066.69, and 431.11, respectively. In isolated rat thoracic aorta, vanylidilol's vasorelaxant effects on phenylephrine (10 micromol/l)-induced contractions were attenuated by removing endothelium and by the presence of L-N(G)-nitro arginine methyl ester (L-NAME; 100 micromol/l), methylene blue (10 micromol/l), 1H-[1,2,4]oxadiazolol[4,3,-a] quinoxalin-1-one (ODQ; 10 micromol/l), tetraethylammonium (10 mmol/l), glibenclamide (1 micromol/l), apamin (1 micromol/l), and charybdotoxin (0.1 micromol/l). In addition, vanylidilol, in an equally antagonistic activity, inhibited phenylephrine-induced phasic and tonic contractions. Intravenous vanylidilol further reduced mean blood pressure in pentobarbital-anesthetized normotensive Wistar rats in a dose-dependent manner. The oral administration of vanylidilol to conscious spontaneously hypertensive rats had a long-lasting hypotensive effect on the heart rate and decreased it in a dose-dependent manner. Furthermore, vanylidilol's vasodilator effect can be attributed in part to the release of NO or NO-related substance from vascular endothelium, while the endothelium-independent mechanism involved in vanylidilol's relaxation is probably linked to the activation of the K(+) channels and the alpha-adrenoceptor blocking activity in these vessels.

Vanillylamide-based propanolamine derivative displays alpha/beta-adrenoceptor blocking and vasodilating properties

A propanolamine derivative with vanillylamide base, KMUP 880602, was first investigated under in vivo and in vitro conditions. IV KMUP 880602 (0.1, 0.5, 1.0, and 2.0 mg/kg) produced dose-dependent hypotensive and bradycardia responses in pentobarbital-anesthetized Wistar rats. KMUP 880602 also markedly inhibited both the tachycardia effects induced by (-)isoproterenol and arterial pressor responses induced by phenylephrine. In isolated guinea pig tissues, KMUP 880602 competitively antagonized (-)isoproterenol-induced positive inotropic and chronotropic effects of the atria and tracheal relaxation responses. The apparent pA2 values KMUP 880602 were 7.24 +/- 0.08 (right atria), 7.42 +/- 0.07 (left atria), and 6.24 +/- 0.06 (trachea). KMUP 880602 also produced a competitive antagonism of norepinephrine-induced contraction in the isolated rat aorta with pA2 values of 7.64 +/- 0.18. In the radioligand-binding assay, [3H]CGP-12177 binding to rat ventricle and lung tissues and [3H]prazosin binding to brain membranes were inhibited by KMUP 880602 with pKi values of 7.27, 6.08, and 8.25, respectively. In isolated rat thoracic aorta, the vasorelaxant effects of KMUP 880602 on phenylephrine-induced contractions were attenuated by pretreatment with tetraethylammonium (10-3 M) and charybdotoxin (10-7 M) but not by glibenclamide, 4-aminopyridine, and apamin. In conclusion, KMUP 880602 is an alpha/beta-adrenoceptor blocker, with selective beta1-adrenoceptor blocking and vascular smooth muscle relaxation activities. Particularly, the vasorelaxant effect of KMUP 880602 is partially mediated by the opening of charybdotoxin-sensitive K+ channel.

The new generation dihydropyridine type calcium blockers, bearing 4-phenyl oxypropanolamine, display alpha-/beta-adrenoceptor antagonist and long-acting antihypertensive activities

A new series of dihydropyridine derivatives, bearing oxypropanolamine moiety on phenyl ring at the 4-position of the dihydropyridine base, were prepared. Oxypropanolamine was synthesized by replacing the phenolic OH of vanillin or other compounds, having a phenyl aldehyde group, with epichlorohydrin, followed by cleavaging the obtained epoxide compounds with tert-butylamine, n-butylamine or 2-methoxy-1-oxyethylamino benzene (guaiacoxyethylamine), respectively. Obtained various oxypropanolamine compounds, still remaining a phenyl aldehyde moiety, were then performed by Hantzsch condensation reaction with methylacetoacetate or ethylacetoacetate, respectively, to give our new series of dihydropyridine linked with the 4-phenyl ring. These compounds were evaluated for inotropic, chronotropic, and aorta contractility that associated with calcium channel and adrenoceptor antagonist activities. Dihydropyridine derivatives that with oxypropanolamine side chain on their 4-phenyl ring associated alpha-/beta-adrenoceptor blocking activities created a new family of calcium entry and the third generation beta-adrenoceptor blockers. Optimizing this research to obtain more potent alpha-/beta-adrenoceptor blocking and long-acting antihypertensive oxypropanolamine on the 4-phenyl ring of dihydropyridine series compounds was thus accomplished and classified as third generation dihydropyridine type calcium channel blockers, in comparison with previous short-acting type nifedipine and long-acting type amlodipine. We concluded that compounds 1a, 1b and 1g showed not only markedly high calcium-antagonistic activity but also the highest antihypertensive effect; compounds 1b, 1c, 1f, 1g, 1i and 1j induced sustained antihypertensive effects are major and attributed to their calcium entry and alpha-adrenoceptor blocking activities in the blood vessel due to their introduction of 2-methoxy, 1-oxyethylamino benzene moiety in the side chain on the 4-phenyl ring of dihydropyridine. Bradycardiac effects of all the compounds 1a-1j resulted from calcium entry and beta-adrenoceptor blocking, which attenuate the sympathetic activation-associated reflex tachycardia in the heart. We selected compound 1b as candidate compound for further pharmacological and pre-clinical evaluation studies.