Effect of bupranolol on CGP 12177-induced relaxation and cAMP accumulation in the guinea pig taenia caecum

• 1.1. The effect of bupranolol on CGP 12177-induced relaxation and cAMP accumulation in the guinea pig taenia caecum was examined.
• 2.2. The relaxant response to CGP 12177 was unaffected by propranolol (∼10⁻⁶ M), whereas that to CGP 12177 was antagonized in a concentration-dependent manner by bupranolol; Schild plot of the data revealed the pA₂ value of 5.61.
• 3.3. CGP 12177 significantly increased cyclic AMP level in this preparation. Bupranolol (10⁻⁴ M) significantly decreased the cyclic AMP level that was elicited by CGP 12177, whereas propranolol (10⁻⁵ M) produced no effect.
• 4.4. These results suggest that bupranolol appears to be an efficient β₃-antagonist in the guinea pig taenia caecum and confirm that the response to CGP 12177 is mediated by β₃-adrenoceptors.

     

Selective and Non-Selective Beta-Blockade in Renin Release

Abstract The effects of two beta-adrenergic receptor blocking drugs, the non-selective propranolol and the beta₁selective metoprolol, were studied on hemodynamics and plasma renin activity (PRA) of healthy volunteers in an ergometric exercise test. Oral doses of 160 mg of propranolol and 200 mg of metoprolol were tested against placebo. The drug plasma concentrations were determined. Heart rate and systolic blood pressure were equal and significantly lower during treatment with both active drugs when compared to placebo. The effect of drugs on exercise heart rate was correlated with the logarithm of drug plasma concentration with both propranolol and metoprolol. Propranolol, but not metoprolol, decreased the basal level of PRA. The ergometric exercise induced a significant rise in PRA after placebo but this increase was partially inhibited by the both active drugs. On the basis of these findings it is suggested that in man the basal level of PRA could be decreased mainly by blocking the beta₂-adrenoceptors. Instead the exercise induced increase of PRA could be inhibited by blocking the beta₁-adrenergic receptors.     

Selective and non-selective beta-blockade in renin release.

The effects of two beta-adrenergic receptor blocking drugs, the non-selective propranolol and the beta1selective metoprolol, were studied on hemodynamics and plasma renin activity (PRA) of healthy volunteers in an ergometric exercise test. Oral doses of 160 mg of propranolol and 200 mg of metoprolol were tested against placebo. The drug plasma concentrations were determined. Heart rate and systolic blood pressure were equal and significantly lower during treatment with both active drugs when compared to placebo. The effect of drugs on exercise heart rate was correlated with the logarithm of drug plasma concentration with both propranolol and metoprolol. Propranolol, but not metoprolol, decreased the basal level of PRA. The ergometric exercise induced a significant rise in PRA after placebo but this increase was partially inhibited by the both active drugs. On the basis of these findings it is suggested that in man the basal level of PRA could be decreased mainly by blocking the beta2-adrenoceptors. Instead the exercise induced increase of PRA could be inhibited by blocking the beta1-adrenergic receptors.     

Comparative beta-adrenoceptor blocking effects and pharmacokinetics of penbutolol and propranolol in man.

1 The beta-adrenoceptor blocking effects of penbutolol were compared with those of propranolol and a placebo in a double-blind trial involving six healthy volunteers. 2 Heart rate (HR), systolic blood pressure (SBP) and peak expiratory flow rate (PEFR) were measured at rest and during vigorous exercise before and at intervals up to 7 h after oral administration of the drugs. In addition, plasma renin activity (PRA) at rest and plasma levels of penbutolol and propranolol were determined. 3 Penbutolol proved to be a non-cardioselective beta-adrenoceptor blocking drug, antagonizing exercise-induced tachycardia, reducing exercise-induced increase in PEFR and decreasing PRA. The beta-adrenolytic potency of penbutolol was shown to be four-fold that of propranolol but the duration of its effect was similar. 4 The peak plasma level of penbutolol was reached 1 h after administration and its half-life was 4.5 h. 5 Comparison of plasma levels and biological activity of penbutolol revealed that after oral administration this drug is transformed into an active metabolite in man.     

Circadian phase dependency of the effects of different beta-receptor blocking drugs on motor activity of rats. Importance of drug lipophilicity

The effects of seven beta-receptor blocking drugs differing in lipophilicity by 3.5 orders of magnitude (propranolol, bupranolol, oxprenolol, metoprolol, sotalol, practolol, atenolol) were studied on the circadian rhythm in motor activity of light-dark-synchronized (light (L): 7-19 h, dark (D): 19-7 h) male rats. Motor activity after i.p. injection of saline or of the racemic mixtures of all drugs and the isomers of propranolol, bupranolol and practolol was measured in groups of 5 rats with a motimeter. Two doses of either drug were injected either at 7:30 a.m. in L or at 7:30 p.m. in D. In L the drugs did either not affect motor activity or even increased motility in comparison to saline. No dosage-dependency was observed in the drug effects in L. In contrast, during D a dosage-dependent decrease in motor activity was found for all compounds. ED50-values of decrease in motility during D were negatively correlated with lipophilicity (partition coefficient) of the compounds. No significant difference was found in the ED50-values of the isomers studied. The results clearly demonstrate a circadian phase dependency in the effects of beta-receptor blocking drugs on motor activity of rats. A dosage-dependent central depressant effect of the drugs could be observed only in D. It is concluded that the central depressant effects of beta-receptor blocking drugs are mainly due to the non-specific, lipophilic property of the drugs and not brought about by a specific blockade of central beta-adrenoceptors.     

Atypical beta-adrenoceptors,different from beta 3-adrenoceptors and probably from the low-affinity state of beta 1-adrenoceptors,relax the rat isolated mesenteric artery

(1) We examined whether beta3- and/or atypical beta-adrenoceptors relax the rat isolated mesenteric artery. (2) Mesenteric arteries precontracted with phenylephrine were relaxed by beta-agonists with the following potencies (pD2): nonselective agonist isoprenaline (6.00)>nonconventional partial agonist cyanopindolol (5.45)>beta2-agonist fenoterol (4.98)>nonconventional partial agonist CGP 12177 (4.19)>beta3-agonist ZD 2079 (3.72). The beta3-agonist CL 316243 1 mm relaxed the vessel only marginally. (3) The concentration-response curves (CRCs) for cyanopindolol, CGP 12177 and ZD 2079 were not affected by the nonselective beta-antagonist propranolol 0.3 microm, the beta2-antagonist ICI 118551 1 microm and by CL 316243 60 microm, but shifted to the right by bupranolol (pA2 5.3-5.7), CGP 20712 (5.4) and SR 59230A (6.5-6.7) (the latter three drugs block atypical and/or beta3-adrenoceptors at high concentrations). (4) The CRC for isoprenaline was shifted to the right by propranolol (pA2 7.0) but, in the presence of propranolol 0.3 microm, not affected by SR 59230A 1 microm. The CRC for fenoterol was shifted to the right by propranolol (pA2 6.9) and ICI 118551 (6.8). (5) Removal of endothelium diminished the vasorelaxant effects of cyanopindolol, CGP 12177 and ZD 2079. (6) Fenoterol and cyanopindolol also relaxed (endothelium-intact) mesenteric arteries precontracted with serotonin. The relaxant effect of cyanopindolol was antagonized by bupranolol to about the same degree as in phenylephrine-contracted vessels. (7) In conclusion, beta2- and atypical beta-adrenoceptors (but not beta3-adrenoceptors) relax the rat mesenteric artery. The atypical beta-adrenoceptor, which is partially located endothelially, may differ from the low-affinity state of the beta1-adrenoceptor.     

Atypical cardiostimulant beta-adrenoceptor in the rat heart: stereoselective antagonism by bupranolol but lack of effect by some bupranolol analogues

1. Atypical beta-adrenoceptors resistant to propranolol, but blocked by bupranolol, increase contractile force and/or frequency of the heart in humans and rats. We compared the potencies of the enantiomers of bupranolol and examined the possible effects of seven bupranolol analogues including bevantolol (BEV) at this receptor in pithed and vagotomized rats. 2. CGP 12177, an agonist of the atypical beta-adrenoceptor, increased heart rate dose-dependently. Its dose-response curve was shifted to the right by S-(-)-bupranolol 10 micro mol kg(-1) by a factor of 8.4, but not affected by the same dose of R-(+)-bupranolol. 3. Desmethylbupranolol and compounds BK-21, BK-22, BK-23 and BK-25 also increased heart rate dose-dependently. The beta(1)-adrenoceptor antagonist CGP 20712 given in combination with the beta(2)-adrenoceptor antagonist ICI 118,551 (0.1 micro mol kg(-1) each) reduced the positive chronotropic action of the five bupranolol analogues without affecting that of CGP 12177. The potencies of the bupranolol analogues to increase heart rate were correlated (r=0.91, P<0.05) with their affinities for beta(1)-adrenoceptor binding sites in rat brain cortex membranes labelled with [(3)H]CGP 12177 (in the presence of ICI 118,551). 4. BK-26 and BEV, 10 micro mol kg(-1) each, had only minor effects on heart rate by themselves and did not antagonize the effect of CGP 12177. However, at 1 micro mol kg(-1), they antagonized the increase in heart rate elicited by the beta(1)-adrenoceptor agonist prenalterol. 5. In conclusion, bupranolol is a stereoselective antagonist at the atypical cardiostimulant beta-adrenoceptor. The effects of the bupranolol analogues are related to the activation or blockade of beta(1)-adrenoceptors, but not of atypical beta-adrenoceptors.     

Beta-adrenoceptor blocking effects and pharmacokinetics of betaxolol (SL 75212) in man.

1 The pharmacological effects and the pharmacokinetics of betaxolol (SL 75212), a new beta-adrenoceptor blocking agent, were compared with those of propranolol and a placebo in a double-blind trial involving six healthy volunteers. 2 Heart rate (HR), myocardial contractile force (MCF), systolic blood pressure (SBP) and peak expiratory flow rate (PEFR) were measured at rest and during vigorous exercise before and at intervals up to 25 h after oral administration of the drugs. In addition, plasma renin activity (PRA) at rest and blood levels of betaxolol and propranolol were determined. 3. Betaxolol proved to be a potent and long-lasting beta-adrenoceptor blocking drug, devoid of intrinsic beta-sympathomimetic activity. Its beta-adrenoceptor blocking action was shown to four-fold that of propranolol at the cardiac and renal levels and to last at least 25 h after drug intake. 4 The peak blood level of betaxolol was reached 2 to 4 hr after its administration, the first-pass loss is likely to be low and the half-life is 12.3 h. These pharmacokinetic data are perfectly consistent with the long duration of the pharmacological effects of betaxolol in man.     

Effect of bupranolol for BRL37344 and noradrenaline-induced relaxations mediating atypical beta/beta3-adrenoceptor in rat oesophageal muscularis mucosae.

We previously suggested that the existence of atypical beta/beta3-adrenoceptor with pA2-values for bupranolol, a non-selective beta-adrenoceptor antagonist, against BRL37344 and noradrenaline were 5.79 and 5.53 in guinea pig taenia caecum, respectively. We furthermore determined the affinity of bupranolol to subclassify atypical beta/beta3-adrenoceptor in rat oesophageal muscularis mucosae, because it is rich in atypical beta/beta3-adrenoceptor. BRL37344 and noradrenaline produced a concentration-dependent relaxation of rat oesophageal muscularis mucosae. The responses to BRL37344 and noradrenaline were resistant to 3x10(-6) M propranolol, 10(-4) M atenolol, and 10(-4) M butoxamine. However, bupranolol antagonized the responses to BRL37344 and noradrenaline in a concentration-dependent manner. Schild plot analyses of bupranolol against BRL37344 and noradrenaline gave pA2-values of 7.06 and 6.96, respectively. These results suggest that bupranolol can distinguish the difference in affinity between atypical beta/beta3-adrenoceptors in rat oesophageal muscularis mucosae and guinea pig taenia caecum. The difference in behavior of bupranolol confirms the existence of some atypical beta/beta3-adrenoceptors subtypes.     

Propranolol-induced relaxation in the rat basilar artery

Propranolol is a non-selective beta-adrenergic receptor blocker used in the treatment of cardiovascular diseases and migraine prophylaxis. Although it has been shown that propranolol dilates the peripheral arteries of rat, its action in the central nervous system vasculature has not been investigated. In this study, the effects of propranolol in rat basilar artery were investigated. Basilar arteries from male Wistar rats were examined in a myograph system. The relaxant effects of propranolol, pindolol, atenolol, pizotifen and methysergide were examined in basilar arteries precontracted by serotonin or PGF2α. Only propranolol and pizotifen induced vasorelaxations; the pD2 values were 5.23 ± 0.13 and 5.94 ± 0.03; respectively. The vasorelaxation induced by propranolol and pizotifen was not affected by endothelium or the presence of l-NOARG and/or indomethacin. The calcium channel blocking activity of propranolol and pizotifen was compared with that of nifedipine in a calcium free solution with high K⁺ (60 mM) concentration. These drugs shifted the concentration–response curves of calcium induced contractions with pA2 values of 5.45 ± 0.04; 7.14 ± 0.09; and 9.22 ± 0.06 respectively. The P2Y receptor agonist UTP was used to induce sustained and stable contractions in basilar artery segments. Nifedipine caused a marked, but an incomplete relaxation. Cyclopiazonic acid, an inhibitor of sarcoplasmic reticulum calcium channels, but not propranolol or pizotifen abolished the remaining tonus after partial relaxations obtained with nifedipine.These results suggest that propranolol causes vasorelaxation by blocking the L-type voltage-gated calcium channels in the rat basilar artery.     

Cardiac action of carazolol and methypranol in comparison with other beta-receptor blockers.

The new beta-blockers 4-(2-hydroxy-3-isopropyl-amino-propoxy)-carbazole (carazolol) and 1-(4-acetoxy-2,3,5-trimethylphenyloxy)-3-isopropylamino-propan-2-ol (methypranol, Disorat) were compared with 14 well-known beta-blocking agents with regard to isoproterenol antagonism (equipotent doses in the rabbit i.v.), acute toxicity (LD50 in mice i.v.) and intrinsic sympathomimetic activity (increase in the heart rate of reserpinized rats i.p.). The following descending order for the equipotent beta-receptor blocking doses was obtained: nifenalol, DCI, pronethalol, practolol, sotalol, alprenolol, bupranolol, toliprolol, propranolol, methypranol, YB 2 pindolol, bunitrolol, oxprenolol, bunolol and carazolol. Carazolol had, in addition, the highest therapeutic index and at beta-receptor blocking doses virtually no intrinsic sympathomimetic activity.     

Effects of (+) and (-)-propranolol on the responses of the human isolated basilar artery to cerebrospinal fluid obtained from patients with subarachnoid haemorrhage and cerebral arterial spasm.

1. The human isolated basilar artery has been used as a model to investigate the aetiology of cerebral arterial spasm associated with rupture of intracranial aneurysms. 2. The isolated artery is contracted by 5-hydroxytryptamine, noradrenaline, six prostaglandins and cerebrospinal fluid from patients with ruptured aneurysms and cerebral arterial spasm. 3. These contractions are reversed by (+/-)--, (+)-- and (--)-propranolol in concentrations known to produce local anaesthetic effects on isolated frog sciatic nerve; the (+) isomer was 2.5 to 10 times more potent (-)-propranolol in antagonising all contractions. 4. As the two isomers are known to have similar local anaesthetic potency but (-)-propranolol has greater beta-adrenoreceptor blocking effects we conclude that the antagonistic effects described do not involve beta-adrenoreceptor blockade. 5. The data indicate that propranolol may be of clinical use in reversing cerebral arterial spasm.     

β-受体阻断剂对异丙肾上腺素提高心肌耗氧量作用的影响

The blockade effect of β-receptor blockers bupranolol and ACC9089 on the increase of heart muscle oxygen consumption by isoprenaline was studied according to Castellucci's method with Warburg's apparatus on thin slices of swine heart muscle instead of the rabbit heart muscle. The results showed that Bupranolol was about 2.5 times more stronger than practolol and about 2 times more stronger than ACC-9089 to block the increase of effects of isoprenaline for swine heart muscle oxygen consumptions on equal molar concentration levels. The results showed also that only the secondary higher concentration of 4 different concentrations of ACC-9089 could block the β-receptor to decrease the heart muscle oxygen consumption in comparison with the control. It was suggested that the highest molar cone. (1.72×10^-3M) of ACC-9089 would probably show an intrinsic sympathomimetic effect which could overlay its blockade effect to β-receptors. That the β-receptor blockers would act as the competitions with isoprenaline to the β-receptors according to their similarity of the side chain chemical structures has been discussed.     

Evidence against beta 3-adrenoceptors or low affinity state of beta 1-adrenoceptors mediating relaxation in rat isolated aorta

1 The presence of beta(3)-adrenoceptors and the low affinity state of the beta(1)-adrenoceptor (formerly "putative beta(4)-adrenoceptor") was investigated in ring preparations of rat isolated aorta preconstricted with phenylephrine or prostaglandin F(2alpha) (PGF(2alpha)). Relaxant responses to isoprenaline, selective beta(3)-adrenoceptor agonists (BRL 37344, SR 58611A, CL 316243) and non-conventional partial agonists (CGP 12177A, cyanopindolol, pindolol) were obtained. 2 In phenylephrine-constricted, but not PGF(2alpha)-constricted rings, relaxations to isoprenaline showed a propranolol-resistant component. 3 In phenylephrine-constricted rings, relaxations to BRL 37344 (pEC(50), 4.64) and SR 58611A (pEC(50), 4.94) were not antagonized by the selective beta(3)-adrenoceptor antagonist SR 59230A (< or =1 microM). CL 316243 (< or =100 microM) failed to produce relaxation. In PGF(2alpha)-constricted rings only SR 58611A produced relaxation, which was not affected by SR 59230A (< or =3 microM). 4 Non-conventional partial agonists produced relaxation in phenylephrine-constricted but not PGF(2alpha)-constricted rings. The relaxation to CGP 12177A was unaffected by SR 59230A (< or =1 microM) or by CGP 20712A (10 microM), reported to block the low affinity state of the beta(1)-adrenoceptor. 5 beta-adrenoceptor antagonists also produced relaxation in phenylephrine-constricted rings with an order of potency of (pEC(50) values): bupranolol (5.5) approximately 38;SR 59230A (5.47) approximately 38;cyanopindolol (5.47)>pindolol (5.30)>alprenolol (5.10)>propranolol (4.83)>ICI 118551 (4.60)>CGP 12177A (4.38) approximately 38;CGP 20712A (4.35). Bupranolol (100 microM), alprenolol (30 microM), propranolol (100 microM) and SR 59230A (10 microM) produced no relaxation in PGF(2alpha)-constricted rings. 6 These results provide no evidence for the presence of functional beta(3)-adrenoceptors or the low affinity state of the beta(1)-adrenoceptor in rat aorta.     

Transdermal delivery of bupranolol: Pharmacodynamics and beta-adrenoceptor occupancy

Summary Bupranolol is a non-selective beta-adrenoceptor antagonist with a K_i-value of 6–15 nmol/l (equivalent to 1.5–4 ng/ml in plasma) at beta₁- (rat salivary gland) and beta₂-adrenoceptors (rat reticulocytes) in receptor binding studies with³H-CGP 12177 in the presence of human plasma. After oral administration of 200 mg bupranolol to healthy volunteers, the maximal plasma concentration was observed within 1.2 h but it only reached a level close to the K_i-value. Elimination from plasma was rapid (t_1/2=2.0 h).Administration of 30 mg bupranolol in a transdermal delivery system (TTS) every 24 h to 6 healthy volunteers for 72 h yielded steady state plasma concentrations 4- to 5-times above the K_i-value as shown by in vitro inhibition of beta-adrenoceptor binding by plasma samples. The pharmacodynamic effect, measured as the reduction in exercise tachycardia, showed a stable inhibitory effect; antagonism of a bolus injection of isoprenaline indicated a 10- to 15-fold right shift of the dose-response curve during the observation period of 72 h.It is concluded that steady-state plasma concentrations and effect of the elsewise rapidly eliminated beta-blocker bupranolol can be achieved by a transdermal delivery system applied each day.Some of the results were presented at the joint meeting of the Belgian, Dutch and German Pharmacological Societies. September 1985, Aachen (Naunyn-Schmiedebergs Arch Pharmacol 330 [Suppl]: R 64The paper is dedicated to Prof. Dr. H. Oelschläger (Frankfurt am Main, FRG) on occasion of his 65th birthday     

RENIN RESPONSE TO GRADED HAEMORRHAGE IN CONSCIOUS RATS

1. A haemorrhage volume/plasma renin activity (PRA) response relationship was established for five levels of acute haemorrhage ranging from 1.5 to 15 ml/kg in conscious rats. In addition, the effects of chronic indomethacin and/or acute propranolol administration on the PRA response to 5 and 10 ml/kg haemorrhage was assessed. 2. Mean arterial pressure decreased in a haemorrhage volume dependent manner which was not significantly altered by indomethacin and/or propranolol. 3. Haemorrhage volumes of 1.5 and 3.0 ml/kg did not significantly alter PRA. At haemorrhage volumes of 5.0 ml/kg and higher, PRA increased in a volume-dependent manner. Propranolol decreased basal PRA levels but had little effect on the response to haemorrhage. Indomethacin had no effect on basal PRA, but attenuated the response to haemorrhage somewhat. When propranolol and indomethacin were combined, the PRA response to haemorrhage was significantly attenuated. 4. The conscious cannulated rat model exhibits predictable and reproducible renin responses to haemorrhage and is an excellent model for studying the control of renin secretion.     

Effects of ethanol and/or cardiovascular drugs on cocaine- and methamphetamine-induced fatal toxicities in mice.

The antidotal effects of antihypertensive cardiovascular (CV) drugs against cocaine (COCA)- and methamphetamine (MA)-induced fatal toxicities were examined in mice. Considering the previously-reported favorable interactions, the effects of CV drugs against combined COCA-ethanol (EtOH) or MA-EtOH toxicities were also evaluated. COCA (75 mg/kg) or MA (18 mg/kg) was administered 5 min after an injection of CV drugs, with or without EtOH (3 g/kg); all drugs were injected intraperitoneally. The CV drugs used were 10 mg/kg diltiazem (DIL), 5 mg/kg nimodipine (NIMO) and 5 mg/kg nitrendipine (NITRE) as calcium channel blockers, 5 mg/kg prazosin (PRA) and 5 mg/kg phentolamine (PHEN) as alpha-adrenergic blocking agents, 10 mg/kg propranolol (PRO) as a beta-adrenergic blocking agent, and 10 mg/kg enalapril (ENA) as an angiotensin converting-enzyme inhibitor. In both the COCA (n = 10) and MA (n = 6) groups, regardless of EtOH or CV drug cotreatment, the fatalities could be divided into the early and late deaths, depending on the survival times, the presence of a temporary recovery from acute toxic symptoms such as observable respiratory and locomotive symptoms, and the presence of the drugs (COCA or MA) in blood samples. The acute toxic symptoms included seizures in both the COCA and MA groups, but they were generally suppressed by EtOH regardless of the mortality rate. Some of the CV drugs, such as PRA and PHEN in the COCA groups and DIL, NIMO, NITRE, PRA and PHEN in the MA groups, also suppressed the seizures. The mortality rate was attenuated by PRA in the COCA groups, and by NIMO, NITRE, PRA and PHEN in the MA groups. In the groups cotreated with EtOH, which has been reported to exacerbate the COCA- and MA-induced cardiotoxicity, the frequency of late deaths was increased. Nevertheless, antidotal effects due to NIMO, NITRE, PRA and ENA in the COCA-EtOH groups, and NIMO, NITRE and PRA in the MA-EtOH groups were observed.     

Characterization of atypical beta-adrenoceptors in the guinea pig duodenum.

The atypical beta-adrenoceptors mediating relaxation in the guinea pig duodenum were studied using catecholamines (isoprenaline, noradrenaline and adrenaline), a selective beta3-adrenoceptor agonist BRL37344 ((R*,R*)-(+/-)-4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phe noxyacetic acid sodium salt) and a non-conventional partial beta3-adrenoceptor agonist CGP12177A ((-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one)). Catecholamines and beta3-adrenoceptor agonists induced concentration-dependent relaxation in this preparation. Propranolol (1 microM) produced only small rightward shifts in the concentration-response curves of these agonists. In the presence of propranolol (1 microM), however, a non-selective beta1-, beta2- and beta3-adrenoceptor antagonist bupranolol caused a concentration-dependent rightward shift of the concentration-response curves for catecholamines and beta3-adrenoceptor agonists. Schild plot analyses of the effects of bupranolol against these agonists gave pA2 values of 6.02 (isoprenaline), 5.98 (noradrenaline), 5.93 (adrenaline), 6.51 (BRL37344) and 5.70 (CGP12177A), respectively, and all Schild slopes were not significantly different from unity. These results suggest that atypical beta-adrenoceptors are present in the guinea pig duodenum and involved in mediating the functional relaxant response.     

Effects ofβ-adrenoceptor antagonist administration on β2-adrenoceptors density in human lymphocytes

Abrupt withdrawal of beta-adrenoceptor antagonists may lead to "rebound-effects". To study the mechanism underlying this phenomenon, the effects of the nonselective beta-adrenoceptor antagonists propranolol [no intrinsic sympathomimetic activity (ISA)], alprenolol (weak ISA) and mepindolol (strong ISA) on lymphocyte beta 2-adrenoceptor density--assessed by (+/-)-[125I]-iodocyanopindolol (ICYP) binding--and plasma renin activity (PRA) were investigated in male healthy volunteers aged 23-35 years. Propranolol treatment (4 X 40 mg/day) increased the density of beta 2-adrenoceptors by 25% after 2 days; concomitantly PRA and heart rate were reduced. During treatment beta 2-adrenoceptor density remained elevated. After withdrawal of propranolol PRA reached pre-drug levels rapidly, while heart rate was significantly enhanced. Beta 2-Adrenoceptor density, however, declined slowly being still significantly increased after 3 days, although propranolol was not detectable in plasma after 24 h. The affinity of ICYP to beta 2-adrenoceptors was not changed during or after treatment. Mepindolol treatment (2 X 5 mg/day) caused a 30% decrease of beta 2-adrenoceptor density and PRA after 2 days; both parameters remained reduced during treatment. After withdrawal, PRA reached rapidly pre-drug levels, whereas beta 2-adrenoceptor density was still after 4 days significantly diminished. The KD-values for ICYP, however, were not changed. During and after treatment heart rate was not affected. Alprenolol treatment (4 X 100 mg/day) led to a rapid fall in PRA, but did not significantly affect beta 2-adrenoceptor density. It is concluded, that the ISA may play an important role in modulating beta 2-adrenoceptor density and hence tissue responsiveness to beta-adrenoceptor stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative β-adrenoceptor blocking effect and pharmacokinetics of bucindolol and propranolol in man

Summary The -adrenoceptor blocking properties and pharmacokinetics of bucindolol 150 mg were compared to those of propranolol 80 mg and a placebo in a double-blind trial in 6 healthy volunteers. Heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressures and peak expiratory flow rate (PEFR) at rest and during vigorous exercise, and plasma renin activity (PRA) at rest, were measured before and at intervals up to 24 h after oral administration of the drugs. Bucindolol reduced exercise tachycardia and decreased exercise PEFR, thus behaving as a non-selective -adrenoceptor blocking drug. In contrast to propranolol, bucindolol did not reduce resting HR and PRA, probably because of its intrinsic sympathomimetic activity. It decreased resting DBP in relation to its peripheral vasodilator properties. The effects of bucindolol developed as early as 30 min after administration and lasted up to 24 h, whereas its T_max and T_1/2 were 1.6 and 3.6 h respectively. Comparison of the time courses of plasma bucindolol and the cardiac -adrenoceptor blockade strongly suggests that in man bucindolol undergoes an extensive first-pass effect, leading to the formation of one or more active metabolites.