The selectivity of beta-adrenoceptor antagonists on cardiovascular and bronchodilator responses to isoprenaline in the anaesthetized dog

Inhibition by salmeterol of increased vascular permeability and granulocyte accumulation in guinea-pig lung and skin

1. The long-acting beta 2-adrenoceptor agonist, salmeterol has been evaluated for its anti-inflammatory effects in the guinea-pig lung and skin. 2. Salmeterol, administered in bronchodilator doses to conscious guinea-pigs by both oral (0.01-1.0 mg kg-1) and inhaled (nebulizer concentration, 0.001-1.0 mg ml-1) routes, inhibited histamine-induced plasma protein extravasation (PPE) into the airway lumen. 3. Inhibition of PPE by salmeterol was long-lasting (greater than 6 h) and was inhibited by prior administration of propranolol (1 mg kg-1, s.c.), indicating an effect mediated by beta-adrenoceptors. 4. Inhaled salbutamol (nebulizer concentration, 0.001-1.0 mg ml-1) also inhibited PPE in guinea-pig lung but, in contrast to salmeterol, this effect was short-lived with substantial loss of activity 2 h after administration. 5. Inhaled salmeterol (0.1 mg ml-1) and salbutamol (1.0 mg ml-1) inhibited the accumulation of neutrophils in guinea-pig lung in response to lipopolysaccharide (100 micrograms ml-1). Salmeterol, but not salbutamol, inhibited the infiltration of eosinophils into the airway lumen in response to platelet activating factor (100 micrograms ml-1). These effects of salmeterol were blocked by prior administration of propranolol (5 mg kg-1, s.c.), indicating that they were also beta-adrenoceptor-mediated. 6. Oral salmeterol (10 mg kg-1, p.o.), but not salbutamol (10 and 100 mg kg-1, p.o.), inhibited zymosan-induced granulocyte accumulation and PPE in guinea-pig skin. Lower doses of salmeterol (0.1 and 1 mg kg-1) inhibited PPE, but not granulocyte accumulation.The effects of salmeterol were blocked by prior administration of propranolol (1mgkg-', s.c.). Both salmeterol and salbutamol inhibited histamine-induced PPE in guinea-pig skin.7. Intradermal salmeterol (10-'mol per site), but not salbutamol, was also effective in inhibiting zymosan-induced granulocyte accumulation and PPE in guinea-pig skin.8. It is concluded that salmeterol, at bronchodilator doses in the guinea-pig, inhibits granulocyte accumulation and PPE, possibly by an action on the vasculature. As this profile of activity is not shared by the shorter-acting compound, salbutamol, it would seem that anti-inflammatory activity is associated with beta-adrenoceptor agonism of long duration. The implications of these findings for the use of salmeterol in the treatment of bronchial asthma are discussed.

Acebutolol: a review of its pharmacology, pharmacokinetics, clinical uses, and adverse effects

Acebutolol is a new hydrophilic, cardioselective beta-adrenergic-blocking agent that possesses partial agonist and membrane-stabilizing activities. In the treatment of mild to moderate essential hypertension, once-daily acebutolol as monotherapy provides effective control in a large majority of patients and produces a further reduction in blood pressure when used concomitantly with diuretics. Acebutolol is as effective as other beta-blocking agents, and in a large, double-blind, parallel study against propranolol was found to cause less reduction in heart rate, and fewer neurologic side effects and patient withdrawals due to adverse effects. Oral acebutolol is also effective in suppressing premature ventricular contractions, and in small numbers of patients generally beneficial results were obtained in supraventricular and ventricular arrhythmias with intravenous administration. These salutary effects are attributable to beta blockade. Controlled clinical trials documented the antianginal actions of oral acebutolol in chronic stable angina pectoris; its efficacy in this regard is comparable to that of other beta-blocking agents. The drug produces smaller decreases in heart rate and cardiac output and alterations in peripheral vascular hemodynamics than beta-blocking drugs without partial agonist activity, and because of its cardioselectivity, it may be used cautiously in patients with bronchospastic disease. Acebutolol has minimal metabolic effects and does not elevate levels of blood lipids during long-term therapy; high-density-lipoprotein cholesterol increased with acebutolol in a small number of patients.

Acebutolol. A review of its pharmacological properties and therapeutic efficacy in hypertension, angina pectoris and arrhythmia

Acebutolol is a cardioselective beta-adrenoceptor blocking drug possessing both partial agonist (intrinsic sympathomimetic) and membrane stabilising activity. In hypertension, it can be administered once or twice daily with equal effectiveness, and has been as effective at lowering blood pressure as propranolol, diuretics, and other beta-blocking drugs (metoprolol, labetalol and atenolol) and more effective than methyldopa. Acebutolol has a significantly smaller effect on resting heart rate than propranolol, metoprolol and atenolol, although direct comparisons with drugs with intrinsic sympathomimetic activity have yet to be undertaken. In both angina and arrhythmia, when administered twice daily it has been as effective as standard therapeutic agents. The side effect profile of acebutolol appears to be comparable to that of other cardioselective beta-blockers. Its relative cardio-selectivity, partial agonist and membrane stabilising activity, hydrophilicity, and considerable extrarenal excretion may offer advantages over some beta-blocking drugs in specific patients. Choosing a beta-blocking agent, however, should be made with a knowledge of pharmacodynamic and pharmacokinetic properties of the various agents and careful consideration of how such properties may be of benefit to an individual patient.

Beta-blocking potency and electrophysiologic effects of acebutolol

The beta-blocking potency of three doses of acebutolol (100, 200, and 600 mg three times a day) has been compared to that of propranolol (30, 60, and 180 mg three times a day) in a double-blind crossover study in 10 healthy volunteers (seven men, three women). On the basis of reduction in resting and exercise heart rates, propranolol was three to four times more potent than acebutolol on a milligram-for-milligram basis. Plasma levels showed large interindividual variation for both agents. Plasma levels were weakly correlated with the degree of beta blockade for both acebutolol (r = 0.333, p less than 0.001) and propranolol (r = 0.381, p less than 0.01). Dose and percent beta blockade were more strongly correlated (propranolol, r = 0.503, p less than 0.001; acebutolol, r = 0.574, p less than 0.001). In 11 patients (10 men, one woman) with coronary artery disease, acebutolol at 1 mg/kg infused over 15 minutes decreased heart rate and slowed conduction, increased the refractoriness of the atrioventricular node without a significant change in the atrial refractoriness, and at plasma levels greater than or equal to 1000 ng/ml slowed His-Purkinje conduction. The comparative potency data suggest that the magnitude of the decrease in the resting and exercise-induced changes in heart rate and double product, in relation to dose of acebutolol, provides quantitative indices for judging adequacy by beta blockade in clinical therapeutics. The use of plasma drug levels, however, does not appear to be helpful in judging the adequacy of beta blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologic properties of acebutolol: relationship of hydrophilicity to central nervous system penetration

Studies in various animal models have shown acebutolol to be a relatively cardioselective beta-adrenoceptor-blocking agent possessing both partial agonist and membrane-stabilizing activities. The latter property may not be significant at clinically used doses. Acebutolol has both antihypertensive and antiarrhythmic effects. As with beta blockers in general, the antihypertensive mechanism of acebutolol is not known. The antiarrhythmic activity of acebutolol may be related to beta blockade. Acebutolol is relatively hydrophilic and does not readily cross the blood-brain barrier, a fact that may be clinically significant in reducing the frequency and severity of central nervous system adverse effects. The pharmacologic profile of diacetolol, acebutolol's major metabolite, is similar to that of the parent compound in beta-blocking potency, cardioselectivity, and partial agonist activity. Diacetolol, however, does not possess membrane-stabilizing activity.

Beta 1-adrenoceptor-mediated amylase release and cyclic AMP accumulation in rat parotid gland tissue

The present study was carried out to determine the relationship of beta 1- and Beta 2-subtype to amylase release and cyclic AMP (cAMP) accumulation in rat parotid tissue. In in vitro experiments, beta-adrenergic agents (isoproterenol and dobutamine)-induced amylase release and cAMP accumulation were all completely inhibited by the beta 1-antagonist metoprolol, but incompletely inhibited by the beta 2-antagonist butoxamine. The beta 2-agonist procaterol caused little or no amylase release or cAMP accumulation. Our results suggest that both amylase release and cAMP accumulation in rat parotid tissue may be selectively induced by beta 1-adrenergic stimulation.

The selectivity of beta-adrenoceptor antagonists on isoprenaline-induced changes in heart rate, blood pressure, soleus muscle contractility and airways function in anaesthetized cats

The beta-adrenoceptor antagonist of propranolol, metoprolol, atenolol and butoxamine in anaesthetized cats has been measured and compared with the activity of four synthetic phenylethanolamine derivatives. The effects of isoprenaline on four parameters in the anaesthetized cat: heart rate, blood pressure, soleus muscle contractility and airway reactance, were measured and the modification of the isoprenaline dose-response relation by each of the antagonist drugs assessed. Parallel shifts in log dose-response curves for isoprenaline were caused by propranolol for all parameters, by metoprolol and atenolol for each parameter except blood pressure, and butoxamine for each except soleus muscle and heart rate. Selectivity of action of the antagonists between different organs was measured by comparing DR10 values, computed from isoprenaline dose-ratios. Propranolol was the most potent antagonist and showed slight selectivity of action on soleus muscle compared with heart. Atenolol and metoprolol were approximately equipotent and were cardioselective at low doses only. Butoxamine was the least potent antagonist and possessed non-beta-adrenoceptor effects on the parameters measured. Each of the new compounds, 4'-bromo-2'-methoxy-N-isopropyl phenylethanolamine, the 4'-chloro- and 4'-methyl analogues, and 4'-methoxy-N-t-butyl phenylethanolamine, was a potent antagonist but did not exhibit any selectivity of action. The results suggest no clear separation of beta-adrenoceptors into beta 1- and beta 2-subclasses in organs of the cat. There is no apparent separation of beta-adrenoceptor-mediated effects on skeletal muscle and airways.

Comparison of the beta 1 and beta 2 adrenoceptor blocking properties of acebutolol and propranolol

The purposes of this study were to evaluate the beta 1 and beta 2 adrenoceptor blocking properties of acebutolol and propranolol and measure the plasma levels of acebutolol, its acetylated metabolite and propranolol. Ten patients with reversible obstructive airways disease and hypertension received two separate dose levels of acebutolol and propranolol for five days each. Cardioselective properties were assessed by determining the beta 1 and beta 2 adrenergic-stimulating effects of terbutaline 5 mg before and at the end of each five-day treatment period. Both acebutolol and propranolol were clinically well tolerated. Following study drug there was a 100 percent inhibition of the beta 1 terbutaline effect, and an approximate 83 percent inhibition of the beta 2 terbutaline effect. There were no clinically significant differences between acebutolol and propranolol. The acetylated acebutolol metabolite accumulated levels two to three times higher than the parent compound, and its effects may have destroyed the cardioselectivity of acebutolol. Thus, acebutolol did not demonstrate clinically relevant cardioselectivity.

The alpha- and beta-adrenoceptor blocking potencies of labetalol and its individual stereoisomers in anaesthetized dogs and in isolated tissues

1 The antagonist potencies of labetalol and each of its four stereoisomers have been compared at alpha 1-, beta 1- and beta 2-adrenoceptors in anaesthetized dogs and in isolated tissues. 2 The RR stereoisomer is a potent, non-selective antagonist at beta-adrenoceptors but has only weak alpha 1-adrenoceptor blocking activity. 3 The SR stereoisomer was the most potent antagonist at alpha 1-adrenoceptors, and it also had similar potency as an antagonist at beta-adrenoceptors. 4 The alpha- and beta-adrenoceptor blocking profile of the RS stereoisomer is intermediate between that of the RR and SR, but the SS stereoisomer is a relatively weak antagonist at both alpha- and beta-adrenoceptors. 5 It is concluded that, although most of the alpha 1-adrenoceptor blocking activity of labetalol is attributable to the SR stereoisomer and nearly all of its beta-adrenoceptor blocking activity resides in the RR stereoisomer, each of the stereoisomers contributes to the overall pharmacological profile of labetalol.

An in vivo procedure for estimating spasmolytic activity in the rat by measuring smooth muscle contractions to topically applied acetylcholine

An in vivo procedure for evaluating potential organ selectivity of spasmolytics has been developed. This involves the determination of comparative potencies, expressed as DR10 of spasmolytics against contractions induced by topical application of acetylcholine on rat colon, rectum and urinary bladder. Experiments with two well known spasmolytics, namely N-butyl-scopolammonium bromide and dicyclomine HCl yielded results consistent with data reported in the literature. This procedure provides a rapid, inexpensive and rather accurate estimate of organ selectivity of spasmolytics.

The effect of carazolol on the cardiovascular responses to adrenaline in stress sensitive pigs

The effect of propranolol, carazolol and acebutolol on the heart rate and blood pressure responses to intravenous adrenaline were examined in conscious Pietrain pigs. All three drugs blocked the tachycardia and vasodilatory responses to adrenaline and induced an increase in vasopressor responsiveness. The likely complications from using non-cardioselective beta blockers for preventing stress-induced deaths in pigs are discussed.

Quantitative assessment of bronchial beta-adrenoceptor blockade in man

1. We describe a method for assessing bronchial beta-adrenoceptor blockade quantitatively in man. Specific airway conductance is measured after increasing doses of inhaled salbutamol and the extent to which the dose-response curve is displaced to the right after beta-adrenoceptor blocking drugs is used to assess bronchial beta-adrenoceptor blockade. 2. Salbutamol dose-response curves were plotted for six normal subjects by measuring sGaw 15 min after increasing doses of inhaled salbutamol. Salbutamol produced a 30-70% increase in sGaw. 3. Salbutamol dose response curves were obtained 2 h after oral practolol (100 mg and 200 mg) and oral propranolol (40 mg and 80 mg) on separate days and were displaced to the right. 4. The mean dose ratios for practolol 100 mg and 200 mg were 1.2 and 2.1 and for propranolol 40 mg and 80 mg they were 21 and 61 respectively.

Exercise responses of healthy subjects in the evaluation of cardioselectivity of beta-blockers

The effects of intravenous propranolol, metoprolol, acebutolol and placebo on exercise-induced changes in heart rate and peak flow rate (PFR) have been studied in a group of healthy subjects. The three beta-blockers produced significant and comparable reductions in exercise-induced tachycardia and the magnitude of the reduction was related to the log plasma concentration of each drug. Significant cardiac beta-blockade was detectable for three hours after giving propranolol and for four hours after metoprolol and acebutolol. The exercise-induced changes in PFR were small and variable and were not significantly affected by any of the drugs. We conclude that, contrary to published reports, exercise-induced changes in heart rate and PFR in healthy subjects do not provide a satisfactory test system for assessing the selectivity of beta-blockers.

The role of beta1- and beta2-adrenoceptors in the inhibition of gastric acid secretion in the dog

1. Characterization of the beta-adrenoceptors mediating inhibition of gastric acid secretion in the conscious Heidenhain pouch dog has been investigated by determination of the effects of propranolol, (+)-propranolol, practolol and H35/25 on salbutamol and isoprenaline-induced inhibition of gastric acid secretion. 2. The gastric antisecretory effect of salbutamol was significantly blocked by propranolol and H35/25 but not by practolol or (+)-propranolol. The effect of isoprenaline was significantly blocked by propranolol and practolol but not by H35/25 or (+)-propranolol. 3. It is concluded that both beta1- and beta2-adrenoceptors can mediate inhibition of pentagastrin-induced gastric secretion in conscious dogs with a Heidenhain pouch. Salbutamol exerts its antisecretory effect through beta2-adrenoceptors, whereas isoprenaline mediates its effects primarily through beta1-adrenoceptors. 4. The results are discussed with regard to the sub-classification of beta-adrenoceptors and to the possible role of adrenoceptors in the physiological control of gastric secretion. 5. In this study it is concluded that the tachycardia induced by isoprenaline or salbutamol is mediated primarily through reflexes activated by beta2-adrenoceptor mediated vasodilatation.

alpha- and beta-receptor blockade of isoproterenol- and norepinephrine-induced effects on regional blood flow and blood flow acceleration

The effects of the beta-receptor blocking agent propranolol (100 microgram/kg i.v.) and of the alpha-receptor blocking agent dihydroergotamine (50 microgram/kg i.v.) on hemodynamic responses to isoproterenol and norepinephrine (both 1--1024 ng/kg) were investigated in anesthetized dogs. The effects studied were: (1) flow in the ascending aorta and the coronary, common hepatic, gastroduodenal, splenic, cranial mesenteric, renal and femoral arteries: (2) maximal flow acceleration in the splenic, cranial mesenteric and femoral arteries; (3) maximal rate of change of left ventricular pressure (LV dP/dt max). Propranolol shifted the dose-response curves for the isoproterenol-induced flow increases in the common hepatic, gastro-duodenal, and cranial mesenteric arteries to the right. It did not influence the flow responses to isoproterenol in the ascending aorta or the coronary, splenic, renal and femoral arteries. Propranolol prevented the decrease of arterial pressure evoked by isoproterenol. Propranolol shifted the isoproterenol-induced increase of LV dP/dt max and maximal blood flow to the same extent. Propranolol blocked the flow to the liver and gastrointestinal tract to a greater extent than the LV dP/dt max and maximal flow acceleration. Propranolol had no effect on the norepinephrine-induced increases in flow in the splenic, femoral and coronary arteries, but blocked the norepinephrine-evoked increases of flow accelerations and LV dP/dt max to the same extent. Dihydroergotamine inhibited the norepinephrine-induced increase in flow in the femoral artery and the decreases in flow in the hepatic, splenic, cranial mesenteric and renal arteries, and reversed the reduction of flow in the gastroduodenal artery. It is argued that dihydroergotamine may inhibit the increase in femoral flow through two mechanisms: (1) blocking the flow reduction to norepinephrine in the abdomen, and thereby passively shunting blood from the abdomen in preference to the femoral bed; (2) attenuating the norepinephrine-evoked reflexogenic femoral vasodilatation. It is concluded that: (1) propranolol is a beta-receptor blocking agent with a preference for blockade of isoproterenol-induced vascular effects; (2) norepinephrine-induced flow increases are not direct actions on vascular beta-receptors; (3) the increase of maximal blood flow accelerations after isoproterenol and norepinephrine is mediated by stimulation of cardiac beta-receptors; (4) dihydroergotamine is an alpha-receptor blocking agent particularly in the splanchnic vascular region.

Cardiac and bronchial beta-adrenoceptor antagonistic potencies of atenolol, metoprolol, acebutolol, practolol, propranolol and pindolol in the anaesthetized dog

1. The beta-adrenoceptor antagonists atenolol, metoprolol, acebutolol, practolol, propranolol and pindolol have been tested for their ability to reduce isoprenaline-induced bronchodilation and tachycardia in the anaesthetized dog. 2. Atenolol, metoprolol, acebutolol and practolol all possessed a similar degree of cardioselectivity in this animal model.

Possible subdivisions among alpha-adrenoreceptors in various isolated tissues

The ratio (expressed in log10 units) of the equieffective concentrations of (+)- and (-)-noradrenaline has been measured in a variety of isolated tissues in the presence of cocaine (1 x 10(-5) M), tropolone (3 x 10(-5) M) and (+/-)-propranolol (5 x 10(-7) to 5 x 10(-5) M). The values obtained fall into 3 distinct and statistically different groups. Firstly, a high group comprising (mean +/- s.e.) mouse vasdeferens (2-78 +/- 0-04), rabbit duodenum (2-91 +/- 0-07) and ileum (2-86 +/- 0-05). Secondly a middle group comprising rabbit vas deferens (2-54 +/- 0-04), bladder neck muscle (2-56 +/- 0-07) and spleen 2-50 +/- 0-02), guinea-pig vas deferens (2-55 +/- 0-10) and bladder neck muscle (2-48 +/- 0-13) and rat deferens (2-40 +/- 0-08) and thirdlya low group comprising the bladder detrusor muscle from both the rabbit (2-08 +/- 0-08) and the guinea-pig (2-07 +/- 0-04). Under the same conditions measurement of pA2 values for phentolamine and piperoxan against noradrenaline gave the following values in rat vase deferens (8-22 +/- 0-07 and 6-72 +/- 0-03 respectively) and mouse vas deferens (8-31 +/- 0-05 and 6-53 +/- 0-07 respectively). The results are discussed in relation to other findings conderning the nature of the alpha-adrenoreceptor in these tissues. In spite of the absence of any significant difference between the potency of the alpha-adrenoreceptor blocking agents in the two species it is suggested that alpha-adernoreceptors may not belong to a single homogenous population but may vary in their characteristics from tissue to tissue.

The effect of (-)-isoprenaline and (+/-)-salbutamol on pepsinogen and acid secretion in the dog

1 The beta-adrenoceptor agonists, (-)-isoprenaline and (+/-)-salbutamol, reduced pepsinogen secretion induced by pentagastrin in conscious dogs with Heidenhaim pouches. 2 (-)-Isoprenaline and (+/-)-salbutamol also reduced gastric acid secretion while producing a moderate tachycardia.

Selectivity of beta-adrenoceptor agonists and antagonists on bronchial, skeletal, vascular and cardiac muscle in the anaesthetized cat

1 The potencies of fifteen beta-adrenoceptor agonists of widely differing chemical structures were compared with that of (-)-isoprenaline on bronchial muscle, soleus muscle, blood pressure and heart rate in the anaesthetized cat. The beta-adrenoceptor antagonist potencies of propranolol and practolol were determined against (-)-isoprenaline in the same model. 2 (-)-Isoprenaline was the most potent agonist and its action was essentially unselective. Thus, on all four parameters the minimal effective dose was 0.003-0.01 mug/kg and maximal or near maximal responses were produced by 0.3-1 mug/kg. Trimetoquinol was also an essentially unselective agonist. 3 For thirteen of the remaining fourteen agonists, potency was similar on bronchial muscle, soleus muscle and blood pressure but significantly lower on heart rate. 4 The remaining agonist - AH 7616 (4-hydroxy-alpha1-[[(1-methyl-3,3-diphenyl-propyl)amino]-methyl]-m-xylene-alpha1, alpha3-diol, acetate) - was also significantly less potent on heart rate than on the other parameters; in addition, it was clearly less potent on soleus muscle and blood pressure than on bronchial muscle when 5-hydroxytryptamine (5-HT) was used to induce bronchospasm. However, when acetylcholine was used instead of 5-HT the potency of AH 7616 on induce bronchospasm. However, when acetylcholine was used instead of 5-HT the potency of AH 7616 on bronchial muscle, soleus muscle and blood pressure was very similar. AH 7616 may therefore possess a specific 5-HT antagonist action in addition to its beta-adrenoceptor agonist action. 5 The fifteen test agonists were longer acting than (-)-isoprenaline and this was particularly true of trimetoquinol and soterenol. 6 The beta-adrenoceptor antagonist potency of propranolol was almost identical on bronchial muscle, soleus muscle and blood pressure and very slightly lower on the heart. Practolol was 10-12 times more potent on the heart than on bronchial muscle, soleus muscle and blood pressure. 7 These findings suggest that it may not be possible to separate the bronchodilating and tremorenhancing properties of beta-adrenoceptor agonists. The results with agonists and antagonists are in accord with Lands' dual beta-adrenoceptor sub-classification.

Comparative effects of acebutolol and practolol on the lipolytic response to isoprenaline

1 The effects of beta-adrenoceptor blockade on the metabolic responses to isoprenaline have been studied in an in vitro system of isolated fat cells and in six normal subjects. 2 The inhibitory effects of varying concentrations of acebutolol, practolol and propranolol on free fatty acid (FFA) release produced by isoprenaline (10(-7) M) were compared in isolated fat cells prepared from rat epididymal adipose tissue. Acebutolol and practolol, at equimolar concentrations, showed a similar inhibitory effect whilst propranolol was approximately 100 times more potent then either drug. At 10(-5)M concentration of propranolol, lipolysis was virtually abolished whilst at the same molar concentration, acebutolol and practolol halved the response. 3 Six healthy volunteers received three successive 15 min intravenous isoprenaline challenges (0.03 mug kg-1 min-1) per individual experiment. The first acted as a control whilst the following two were given either after single oral doses of placebo, acebutolol or practolol. The mean (+/- s.e. mean) basal FFA level was 0.77 +/- 0.06 mE1/1 and subsequent resting values after the administration of placebo or beta-adrenoceptor blocker were not significantly different. 4 Acebutolol inhibited the respective mean rises in FFA, produced by both post-control isoprenaline challenges, by (mean +/- s.e. mean) 70 +/- 4% and 84% +/- 5%. The comparable figures for practolol were 33 +/- 15% and 24 +/- 20%. The higher serum concentration of acebutolol produced greater inhibition but correlation of log serum concentration of the drug with percentage inhibition of FFA rise did not achieve significance. 5 Administration of isoprenaline, acebutolol or practolol did not significantly alter serum glucose, triglyceride or cholesterol levels. 6 Acebutolol and practolol effectively blocked the isoprenaline-induced tachycardia. The degree of blockade produced by practolol was greater than its inhibitory effect on FFA release. The diatolic fall in blood pressure in response to isoprenaline was abolished by acebutolol suggesting that its beta-adrenoceptor blocking action encompasses peripheral vascular sites. The comparable effect with practolol was a partial inhibition of the diastolic fall.

Cardiac and pulmonary effects of acebutolol

In a double-blind randomised study, single intravenous doses of propranolol (0-1 mg. per kg.), practolol (1 mg. per kg.), acebutolol (1 mg. per kg.), or placebo were each administered at weekly intervals to six healthy volunteers. Forced expiratory volume in 1 second (F.E.V.1), resting and exercise heart-rate, and resting and exercise peak flow-rate (P.F.R.) were determined before and at 2, 3, 4, and 6 hours after each treatment. Venous blood-samples were also obtained at these times. Compared with placebo, resting heart-rate was reduced after all three drugs, but the corresponding differences in exercise heart-rate were much greater, more consistent, and of greater statistical significance. At 2, 3, and 4 hours when acebutolol and propranolol produced equivalent cardiac beta-blocking activity (judged by reductions in exercise heart-rate), their mean plasma concentratios were in the ratio of about 8/1; and at 2 hours when practolol and acebutolol gave rise to almost equivalent cardiac beta blockade, their mean plasma concentratio ration was 3/1. At times, reductions in F.E.V.1 and resting P.F.R. after propranolol (but not after practolol or acebutolol) were significantly greater than the corresponding changes after placebo. The reductions in exercies P.F.R. after propranolol (6 hours) and acebutolol (4 hours) (but not after practolol) were significantly greater than the changes after placebo. Changes in F.E.V.1, resting and exercise P.F.R. after propranolol, and the corresponding changes after practolol, were significantly different, all of which confirmed that practolol was more cardioselective than propranolo. In general, the reductions in F.E.V.1 and resting P.F.R. after acebutolol were slightly smaller than after propranolol, excepting at 6 hours when the difference between them was significant. The reductions in exercise P;F.R. after acebutolol and propranolol were of the same order, there being no significant differences between the two, whereas the reductions after acebutolol were clearly greater than the corresponding changes after practolol, the differences being significant at 2, 3, and 4 hours.