Enhancement of physiological finger tremor by intravenous isoprenaline infusions in man: evaluation of its role in the assessment of beta-adrenoceptor antagonists

The effects of chronic dosing on the beta 1 and beta 2-adrenoceptor antagonism of betaxolol and atenolol

Six normal subjects were given once daily treatment for 15 days with placebo (PL), betaxolol 10 mg (B10), 40 mg (B40); atenolol 100 mg (A 100); and nadolol 40 mg (N40). Measurements of beta 1-adrenoceptorblockade (reduction of exercise heart rate) and of beta 2-adrenoceptor-blockade (attenuation of isoprenaline induced finger tremor) were made after the first, eighth and fifteenth doses of each drug. Plasma concentrations showed dose related increases between 10 mg and 40 mg doses of betaxolol, and there was significant drug accumulation at steady state compared with after single dosing. The reduction in exercise heart rate (EHR) with B10 was less in comparison with all other treatments. There were no significant differences in effects between single and chronic-dosing for any of the treatments (% reduction EHR compared with placebo, on days 1 and 15): B10 (18.2, 19.0), B40 (28.6, 26.5); A100 (22.7, 23.1); N40 (26.6, 23.8). Dose-ratios for attenuation of isoprenaline-induced finger tremor (IT100) were significantly greater with B40 compared with B10 or A100 (no dose-ratio for finger tremor could be calculated for N40). There were no differences between single and chronic-dosing (IT100 dose-ratios on days 1 and 15): B10 (3.0, 2.5), B40 (4.4, 5.3); A100 (3.0, 3.0). The attenuation of isoprenaline-induced chronotropic response (IH25) by N40 was significantly greater in comparison with all other treatments. IH25 dose-ratios (on days 1 and 15) were as follows: B10 (2.8, 3.6), B40 (5.1, 5.8); A100 (3.6, 3.6); N40 (19.0, 17.4).(ABSTRACT TRUNCATED AT 250 WORDS)

A dose-ranging study to evaluate the beta 1-adrenoceptor selectivity of bisoprolol

A dose-ranging study was performed to compare the beta 1-adrenoceptor selectivity of bisoprolol with that of atenolol and nadolol. Seven normal subjects (mean age 26 y) were given single oral doses of bisoprolol 5 mg (B5), 10 mg (B10), 20 mg (B20); atenolol 50 mg (A50), 100 mg (A100); nadolol 40 mg (N40); and placebo (PL), in a single blind randomised cross-over design. Beta 2-adrenoceptor responses were assessed by attenuation of finger tremor and cardiovascular responses to graded isoprenaline infusions. Dose-response curves were constructed, and doses of isoprenaline required to increase finger tremor by 100% (IT100), heart rate by 25 beats/min (IH25), SBP by 25 mmHg (IS25), cardiac output by 35% (IC35), and decrease DBP by 10 mmHg (ID10), after each treatment were calculated. These indices were compared with placebo response and expressed as dose-ratios. Exercise heart rate (EHR) was used to assess beta 1-adrenoceptor blockade. There were dose-related increases in plasma concentrations of bisoprolol and atenolol. Reduction of EHR was significantly less with B5 (16.8%) in comparison with all other treatments: B10 21.9%, B20 23.1%; A50 22.5%, A100 22.6%; N40 22.9%. There were small but significant reductions in isoprenaline-induced tachycardia with bisoprolol and atenolol, although mean dose-ratios were considerably less in comparison with N40 (IH25 dose-ratios): B5 2.55, B10 3.18, B20 3.93, A50 2.91, A100 4.89, N40 17.23. There were similar patterns for the other isoprenaline responses. These results show that conventional doses of bisoprolol (10 mg) and atenolol (50 mg) produced equal antagonism of beta 1 and beta 2-adrenoceptors, and therefore possess equal degrees of beta 1-adrenoceptor selectivity.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of time and dose on the relative beta 1- and beta 2-adrenoceptor antagonism of betaxolol and atenolol

1. Six normal subjects were given single oral doses of betaxolol 10 mg (B10), 40 mg (B40), 80 mg (B80); atenolol 50 mg (A50), 200 mg (A200); or placebo (PL). Measurements of beta 1-adrenoceptor blockade (reduction of exercise heart rate) and of beta 2-adrenoceptor blockade (attenuation of isoprenaline responses) were made at baseline, and at 2, 4, 6, 8 and 24 h after drug ingestion. 2. Mean values for Cmax and tmax were as follows: B10 (33 ng ml-1, 3.7 h), B40 (84 ng ml-1, 4.0 h), B80 (179 ng ml-1, 3.7 h); A50 (261 ng ml-1, 2.7 h), A200 (1369 ng ml-1, 2.0 h). 3. Reduction of exercise heart rate (EHR) occurred in dose-dependent fashion up to a ceiling at B40 (as % reduction c.f. placebo, at peak and 24 h): B10 16.2 to 10.2%, B40 27.1 to 16.2%, B80 27.0 to 18.7%; A50 20.9 to 9.1%, A200 28.8 to 15.8%. There were also dose-related increases in beta 2-adrenoceptor antagonism (IT100 dose ratios, at peak and 24 h): B10 2.1 to 1.2, B40 4.7 to 2.6, B80 6.0 to 4.7; A50 2.0 to 1.2, A200 4.7 to 1.8. There were similar trends for attenuation of heart rate and DBP responses to isoprenaline. 4. Ratios of beta 1:beta 2-adrenoceptor antagonism were calculated (as % reduction EHR divided by IT100 dose ratio); to provide an index of beta 1-adrenoceptor selectivity at peak and 24 h: B10 7.7 to 8.5, B40 5.8 to 6.2, B80 4.5 to 4.0; A50 10.5 to 7.6, A200 6.1 to 8.8.(ABSTRACT TRUNCATED AT 250 WORDS)

A dose-ranging study to evaluate the beta-adrenoceptor selectivity of single doses of betaxolol

1. Six normal subjects were given single oral doses of betaxolol 10 mg (B10), 20 mg (B20), 40 mg (B40), 80 mg (B80), propranolol 40 mg (P40), or placebo (PL) in a single-blind randomised cross-over design. 2. beta 1-adrenoceptor blockade was assessed by reductions in exercise heart rate. Betaxolol produced dose-related reductions in exercise heart rate (beats min-1) up to a ceiling at B40, after which B80 showed a lesser effect: (158 +/- 8 PL, 128 +/- 3 B10, 123 +/- 2 B20, 116 +/- 4 B40, 136 +/- 10 B80, 135 +/- 4 P40). All doses of betaxolol (except B80) produced greater reductions compared with P40: (B10 P less than 0.001, B20 P less than 0.005, B40 P less than 0.001). 3. beta 2-adrenoceptor blockade was assessed by attenuation of finger tremor and cardiovascular responses to graded infusions of i.v. isoprenaline. Dose-response curves were constructed and the doses required to increase heart rate by 25 beats min-1, finger tremor by 200%, calf blood flow by 0.5 ml dl-1 min-1, and decrease diastolic blood pressure by 10 mm Hg, after each treatment were calculated. These were then compared with placebo responses and expressed as dose-ratios. 4. Dose-ratios for finger tremor showed significant attenuation by all doses of betaxolol (compared with PL): B10 1.5 +/- 0.18 (P less than 0.05), B20 2.62 +/- 0.45 (P less than 0.005), B40 2.55 +/- 0.33 (P less than 0.001), B80 2.48 +/- 0.48 (P less than 0.01); and by P40 6.49 +/- 1.12 (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of airways, tremor and chronotropic responses to inhaled salbutamol in the quantification of beta 2-adrenoceptor blockade

1. The purpose of the study was to assess and compare the effects of inhaled salbutamol on heart rate (HR), finger tremor (Tr) and specific airways conductance (sGaw) in the measurement of beta 2-adrenoceptor blockade in normal subjects. 2. Five healthy volunteers were given oral doses of atenolol 50 mg, 100 mg, 200 mg (A50, A100, A200), propranolol 40 mg (P40) or identical placebo (P1) in a single-blind crossover design. 3. Three hours after drug ingestion, dose-response curves were constructed using cumulative doses of inhaled salbutamol: 200 micrograms, 700 micrograms, 1700 micrograms, 3200 micrograms, 6200 micrograms. HR, Tr and sGaw were measured at each dose increment, made every 20 min. 4. Increasing doses of atenolol were associated with progressive reduction in salbutamol induced beta-adrenoceptor responses. The greatest attenuation occurred with propranolol. These effects on beta-adrenoceptor responses were similar for HR, Tr and sGaw. Geometric mean dose ratios (compared with placebo) for A50, A100, A200 and P40 were as follows HR: 1.98, 2.75, 4.29; Tr: 1.60, 3.78, 6.34, 80.50; sGaw: 1.08, 4.35, 12.30, 66.0 (no dose ratio was obtained for HR with P40). 5. These results showed that atenolol and propranolol attenuated the effects of salbutamol on HR to a similar degree as Tr and sGaw. Furthermore, the variability was least in the measurement of chronotropic responses, suggesting that this may be used to quantify beta 2-adrenoceptor antagonism. The beta 1-adrenoceptor selectivity of atenolol was a dose-dependent phenomenon, although the beta 2-adrenoceptor blockade of A200 was much less than with P40.

Evaluation of the metabolic responses to inhaled salbutamol in the measurement of beta 2-adrenoceptor blockade

The aim of the present study was to evaluate whether metabolic responses to inhaled salbutamol may be used to measure the cardioselectivity of beta-adrenoceptor antagonists. We therefore studied the effects of oral doses of atenolol 50 mg, 100 mg, 200 mg (A50, A100, A200), propranolol 40 mg (P40), and placebo (Pl) on the hypokalaemic (K) and hyperglycaemic (Glu) responses to inhaled salbutamol in five healthy subjects. Increasing doses of atenolol were associated with a progressive attenuation of delta K compared with placebo: -0.72 mmol.l-1 (Pl) vs -0.20 mmol.l-1 (A200). However, delta K with A200 was significantly different from the response with P40: +0.12 mmol.l-1. There were partial reductions in the hyperglycaemic response with the beta-adrenoceptor antagonists, although this was only significant (compared with Pl) for P40: delta Glu 1.92 mmol.l-1 (Pl) vs 0.76 mmol.l-1 (P40). These results show that beta 2-adrenoceptor blockade by atenolol is a dose-dependent phenomenon, which may be measured by the attenuation of salbutamol-induced hypokalaemia. However, beta 2-adrenoceptor blockade by atenolol 200 mg was less than that by propranolol 40 mg. The glucose response to salbutamol was only partially blocked by propranolol and may therefore not be suitable to assess beta 2-adrenoceptor antagonism.

Characterization of the beta-adrenoreceptors which mediate the isoprenaline-induced changes in finger tremor and cardiovascular function in man

We have studied the contribution of beta 1- and beta 2-adrenoceptors to the isoprenaline-induced changes in heart rate, blood pressure, forearm blood flow, peripheral vascular resistance, and finger tremor. This was achieved by a comparison of the effects of atenolol 50 mg, ICI 118551 25 mg, propranolol 80 mg, atenolol 50 mg combined with ICI 118551 25 mg, propranolol 80 mg combined with ICI 118551 25 mg, and placebo. Atenolol 50 mg and ICI 118551 25 mg caused similar attenuations in the isoprenaline-induced changes in heart rate and diastolic blood pressure, but the responses after the combination of atenolol and ICI 118551 were similar to those after propranolol 80 mg. There was no difference in the forearm blood flow responses to isoprenaline after atenolol 50 mg and ICI 118551, but atenolol 50 mg did not reduce peripheral vascular resistance compared with placebo. Both responses after treatment with atenolol combined with ICI 118551 were similar to those after propranolol 80 mg. Finger tremor responses to isoprenaline were antagonized by ICI 118551 alone and in combination with propranolol and atenolol but not by atenolol alone, suggesting that the response is beta 2-adrenoceptor-mediated. We conclude that the cardiovascular responses to isoprenaline are mediated by both beta 1- and beta 2-adrenoceptors, whereas the finger tremor response is mediated by beta 2-adrenoceptors.

The assessment of the beta-adrenoceptor blocking activity and cardioselectivity of Koe 3290 in normal subjects

1. The beta-adrenoceptor antagonist activity, cardioselectivity and antilipolytic properties of Koe 3290 were investigated in healthy subjects. 2. Koe 3290 12.5, 25, 50 and 100 mg, atenolol 25, 50 and 100 mg and placebo were given in double-blind randomised order to eight subjects. All doses of both Koe 3290 and atenolol reduced supine, standing and exercise heart rate (P less than 0.02). From 2 to 8 h after administration the exercise heart rate after Koe 3290 100 mg was similar to that for atenolol 50 mg. 3. The cardioselectivity of Koe 3290 and atenolol was compared. Koe 3290 50, 100 and 150 mg, atenolol 50 and 100 mg and placebo were given to six subjects in a double-blind random order. Isoprenaline dose-response curves were constructed for cardiovascular parameters and finger tremor. 4. For doses which were equipotent at the beta 1-adrenoceptor (Koe 3290 100 mg and atenolol 50 mg) atenolol caused less attenuation of heart rate, diastolic blood pressure, forearm blood flow and finger tremor (P less than 0.02). 5. There was no difference in the isoprenaline-induced changes in serum free fatty acids, blood glucose, plasma lactate or potassium after Koe 3290 and atenolol. Koe 3290 attenuated the rise in serum insulin more than atenolol (P less than 0.02). 6. Koe 3290 is an effective beta-adrenoceptor blocking drug in man. It is not as cardioselective as atenolol and does not possess specific antilipolytic properties.

Pharmacologic aspects of cardioselectivity in a beta-blocking drug

Beta 2 adrenoceptors have been subdivided into beta 1 and beta 2 receptors, both by the varying response of different tissues to sympathomimetic amines and, more recently, by radioligand-binding techniques. It would appear that beta 1 receptors occur predominantly in the heart, whereas beta 2 receptors are found in lungs, peripheral blood vessels and uterus, and are also involved with glycogenolysis and glucagon and insulin secretion. In addition, the distribution of beta 1 receptors appears to relate to the density of sympathetic innervation of an organ or tissue, but tissues without sympathetic innervation are found to contain beta 2 receptors. Thus, beta 1 adrenoceptors may be considered as physiologically innervated receptors mediating responses to neuronally released norepinephrine, and beta 2 receptors as mediating responses to circulating catecholamines, particularly epinephrine. Radioligand-binding studies have also shown that the heart contains beta 2 receptors and the lung beta 1 receptors, but these are in the minority, and their role has not been identified. For many years, cardioselective beta 1-adrenoceptor antagonists have been available. This was considered to be a dose-dependent phenomenon but recent evidence has cast doubt on the concept that cardioselectivity is lost during dose increases within the therapeutic range. Nevertheless, even small doses of cardioselective drugs may show some beta 2-receptor antagonism, and may have adverse effects on patients with obstructive airways disease. Finally, nonselective drugs may result in a diastolic pressor effect in the presence of circulating catecholamines in contrast to the "vascular sparing" seen with cardioselective drugs.

Effects of beta-adrenoceptor blockade on heart rate and physiological tremor in diabetics with autonomic neuropathy. A comparative study of epanolol, atenolol and pindolol

Eight diabetics with autonomic neuropathy were given single oral doses of epanolol (200 mg), atenolol (50 mg), pindolol (5 mg) and placebo in a double-blind randomised order at weekly intervals. Supine resting heart rate, physiological tremor and blood glucose were measured before, 2 and 4 h after dosing, and ambulatory heart rate monitored for 24 h. Supine resting heart rate was significantly lowered by atenolol both at 2 and 4 h, and increased on pindolol at 4 h. Heart rate was unaffected by epanolol compared with placebo. Heart rate during the 'waking' period (14.00-23.00 h) was lower than placebo after epanolol and atenolol but unaffected by pindolol. During the 'sleeping' period (23.00 h-08.00 h) heart rate was significantly increased by pindolol, lowered with atenolol and unaffected on epanolol. Pindolol significantly increased physiological tremor at 4 h. No differences were seen between epanolol, atenolol and placebo. Plasma glucose was significantly increased by pindolol 2 h after dosing. These results suggest that pindolol probably produces its partial agonist activity at both beta 1- and beta 2-adrenoceptors, while the partial agonist activity of epanolol is beta 1-selective. Despite abnormal cardiovascular reflex tests in these diabetics, the heart rate responses obtained in this study after beta-adrenoceptor blockade were surprisingly normal, and suggest that the concept of 'cardiac denervation' in diabetes requires modification.

The assessment in man of the beta-adrenoceptor blocking activity and cardioselectivity of H-I 42 BS, a long acting beta-adrenoceptor blocking drug

The pharmacokinetic and pharmacodynamic effects of the beta-adrenoceptor antagonist H-I 42 BS were examined in healthy subjects. In an open dose ranging study, H-I 42 BS 50, 100, 200 and 400 mg were given as single oral doses to four subjects. H-I 42 BS 400 mg caused maximum reduction in exercise heart rate (20.4 +/- 1.0%--mean +/- s.d.) at 4 h and still reduced exercise heart rate at 96 h (18.4 +/- 7.2%). Seven subjects received in double-blind, randomised order, single oral doses of H-I 42 BS 50, 100 and 200 mg, atenolol 50 and 100 mg and placebo. H-I 42 BS 400 mg was given in a single blind manner as the last dose of the study. Both H-I 42 BS and atenolol reduced supine and standing heart rate and systolic blood pressure (P less than 0.05) although atenolol had the more marked effect. The maximum percent reduction of exercise heart rate after H-I 42 BS 50 mg was 10.9 +/- 7.1%, after 100 mg was 18.7 +/- 5.8%, after 200 mg was 20.6 +/- 6.4% and after 400 mg was 21.9 +/- 8.2%. H-I 42 BS 400 mg still caused 11.0 +/- 3.5% reduction at 168 h. Atenolol 50 mg caused maximum percent reduction of exercise heart rate of 26.0 +/- 6.0% but did not reduce exercise heart rate after 24 h. The mean peak plasma concentrations for all doses of H-I 42 BS occurred at 5.1 +/- 1.5 h. The plasma elimination half-life was 47.6 +/- 8.1 h. There was a linear correlation between the dose and AUC0-infinity (r = 0.97). The cardioselectivity of H-I 42 BS and atenolol was compared. Six subjects received in double-blind random order H-I 42 BS 100 and 400 mg, atenolol 50 mg and placebo. After each dose, graded infusions of isoprenaline were given until the heart rate increased by 50 beats min-1. Dose-response curves for heart rate, diastolic blood pressure, forearm blood flow and finger tremor were constructed. There was no difference in the dose-response curves for forearm blood flow or finger tremor after H-I 42 BS 400 mg or atenolol 50 mg. Atenolol 50 mg caused more attenuation (P less than 0.01) of the diastolic blood pressure response. These results indicate that H-I 42 BS is a cardioselective beta-adrenoceptor antagonist with a long duration of action in man.

Effects of the beta 2-adrenoceptor antagonist ICI 118,551 on exercise tachycardia and isoprenaline-induced beta-adrenoceptor responses in man

ICI 118,551, 5 to 80 mg orally, did not significantly alter resting heart rate or blood pressure. In doses less than 40 mg the reduction in exercise tachycardia was under 10 beats/min. ICI 118,551, 10 to 40 mg, did not appear to reduce the maximum rise in systolic pressure with isoprenaline but did attenuate the changes in diastolic pressure, forearm blood flow and finger tremor. It also attenuated the isoprenaline-induced changes in serum glucose, insulin and potassium. On these observed changes, the effect of ICI 118,551 20 mg was similar to that of 40 mg and of propranolol 10 mg, but greater than that of atenolol 25 mg. An isoprenaline tachycardia was attenuated by all doses of ICI 118,551 studied. After atropine (0.04 mg/kg) ICI 118,551 20 mg still significantly reduced the effects of isoprenaline suggesting that functional beta 2-adrenoceptors may be present in the human heart. In doses less than 40 mg, ICI 118,551 appears to be a selective and competitive antagonist of beta 2-adrenoceptors in man.