Immediate haemodynamic effects of a novel partial agonist, beta 1-adrenoceptor blocking drug ICI 141,292 after intravenous administration to healthy young volunteers and patients with ischaemic heart disease

Effects of epanolol, a selective beta1-blocker with intrinsic sympathomimetic activity, in patients with ischemic left ventricular dysfunction

Recently, different beta-blockers have been shown to be effective in the treatment of chronic heart failure (CHF), but the importance of their ancillary properties is not clear. Epanolol is a selective beta1-blocker with intrinsic sympathomimetic activity, which has been shown useful in angina pectoris, but its value in patients with left ventricular (LV) dysfunction and CHF is unknown. We examined the effects of epanolol in patients with LV dysfunction (n = 8; mean LV ejection fraction, 0.33 +/- 0.08) and compared them with patients with normal LV function (n = 8; mean LV ejection fraction, 0.52 +/- 0.04). Measurement of invasive hemodynamics and neurohormones was performed at rest and during myocardial ischemia, which was induced by atrial pacing. All measurements were performed before and after epanolol. Before epanolol, pacing-induced ischemia led to a similar increase in norepinephrine and coronary sinus blood flow in both groups. After epanolol, the increase in neurohormones was more pronounced in the group with LV dysfunction (norepinephrine, 1,130 +/- 164 pg/ml for patients with LV dysfunction vs. 637 +/- 41 pg/ml for normal subjects; p < 0.05). A similar effect was observed for angiotensin II. Further, in the LV-dysfunction group, coronary sinus blood flow increased less, and coronary vascular resistance decreased less (both values, p < 0.05). Despite the fact that the increase in double product was decreased to a similar extent in both groups, ischemia was reduced only in normal LV function (p < 0.05). In ischemic LV dysfunction, neurohumoral activation after epanolol may impair adequate coronary flow response, and this may limit its antiischemic properties. Because of the small size of the study, no definitive inference on the clinical benefit of epanolol in patients with ischemic LV function can be made from this study.

Evaluation of partial beta-adrenoceptor agonist activity

A partial beta-adrenoceptor (beta-AR) agonist will exhibit opposite agonist and antagonist activity depending on the prevailing degree of adrenergic tone or the presence of a beta-AR agonist with higher intrinsic activity. In vivo partial beta-AR agonist activity will be evident at rest with low endogenous adrenergic tone, as for example with chronotropicity (beta 1/beta 2), inotropicity (beta 1) or peripheral vasodilatation and finger tremor (beta 2). beta-AR blocking drugs which have partial agonist activity may exhibit a better therapeutic profile when used for hypertension because of maintained cardiac output without increased systemic vascular resistance, along with an improved lipid profile. In the presence of raised endogenous adrenergic tone such as exercise or an exogenous full agonist, beta-AR subtype antagonist activity will become evident in terms of effects on exercise induced heart rate (beta 1) and potassium (beta 2) responses. Reduction of exercise heart rate will occur to a lesser degree in the case of a beta-adrenoceptor blocker with partial beta 1-AR agonist activity compared with a beta-adrenoceptor blocker devoid of partial agonist activity. This may result in reduced therapeutic efficacy in the treatment of angina on effort when using beta-AR blocking drugs with partial beta 1-AR agonist activity. Effects on exercise hyperkalaemia are determined by the balance between beta 2-AR partial agonist activity and endogenous adrenergic activity. For predominantly beta 2-AR agonist such as salmeterol and salbutamol, potentiation of exercise hyperkalaemia occurs. For predominantly beta 2-AR antagonists such as carteolol, either potentiation or attenuation of exercise hyperkalaemia occurs at low and high doses respectively. beta 2-AR partial agonist activity may also be expressed as antagonism in the presence of an exogenous full agonist, as for example attenuation of fenoterol induced responses by salmeterol. Studies are required to investigate whether this phenomenon is relevant in the setting of acute severe asthma.

A placebo controlled comparison of the effects of metoprolol and celiprolol on echo-Doppler measurements of cardiovascular function in normal volunteers

1. This study used a continuous-wave echo-Doppler method (Exerdrop) to investigate the effects of beta-adrenoceptor antagonism and partial agonism on cardiovascular responses at rest and during dynamic exercise. 2. A double-blind, randomised, placebo controlled comparison of metoprolol (50 mg) and celiprolol (200 mg) was undertaken in nine normal volunteers; single oral doses of medication were administered at weekly intervals. Rest and exercise (supine bicycle) haemodynamics were assessed at 0, 2, 4, 6 and 8 h following dosing. 3. Before dosing and after placebo, the aortic flow velocity, acceleration and velocity integral increased progressively during exercise, as did heart rate, blood pressure and cardiac output. 4. Following metoprolol 50 mg, heart rate was significantly reduced without change in systolic or diastolic blood pressure. Echo-Doppler peak acceleration and velocity decreased at rest. On exercise, heart rate and systolic blood pressure fell significantly; the increase in acceleration was significantly blunted compared with placebo (a decrease of 15.2% at rest and 22.9% at 75 watts; P < 0.01 vs placebo). Peak velocity fell significantly by 75 watts exercise. 5. Celiprolol 200 mg at rest significantly increased systolic blood pressure, peak acceleration and velocity. On exercise celiprolol, in contrast to metoprolol, did not reduce peak acceleration or peak velocity; however exercise heart rate and systolic blood pressure were significantly reduced. The difference between celiprolol and metoprolol in respect of peak acceleration persisted over the 8 h of the study. 6. These differences between metoprolol and celiprolol are compatible with the partial agonism of celiprolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute systemic and antiischemic effects of epanolol in patients with coronary artery disease

Antiischemic effects of beta 1-blocking agents are based on intrinsic negative inotropic and chronotropic properties. Partial beta 1-agonistic activity, although useful in preserving cardiac function, may counteract such antiischemic properties by modulating the intrinsic negative cardiac effects of beta-blockade. To investigate the acute hemodynamic and antiischemic profile of epanolol, a cardioselective beta 1-antagonist and partial agonist, 20 patients with left coronary artery disease underwent two incremental atrial pacing tests, 45 minutes before (APST I) and 15 minutes after (APST II) 4 mg intravenous epanolol, administered over 5 minutes. Additional measurements were carried out at 1, 3, 5, 10, and 15 minutes after epanolol, at basal and fixed heart rates. Epanolol immediately reduced heart rate with a maximum of 10% at 15 minutes and decreased contractility (Vmax) by 7% (both p < .05), whereas cardiac output fell temporarily by 9% (p < .05). Other hemodynamic parameters did not change, except for a significant 11% reduction in myocardial oxygen demand. Despite comparable pacing conditions, both the double product and contractility decreased significantly less during APST II, resulting in a 17% lower myocardial oxygen consumption (p < .05). Myocardial ischemia was markedly reduced, indicated by normalization of lactate metabolism [lactate extraction 16 +/- 7% vs. -7 +/- 8% (APST I)], less ST depression (21%), and modulation of LV end-diastolic pressure postpacing (all p < .05 vs. APST I), whereas angina was absent or less in 14 patients. None of the patients reported an adverse effect. Thus, under resting conditions intravenous epanolol induces moderate, short-lasting negative chronotropic and inotropic effects, but does not alter cardiac pump function or vascular resistance, reflecting its additional beta 1-agonistic properties. Alternatively, during pacing it still reduces ischemia through negative inotropic effects and diminishes myocardial oxygen demand, reflecting its beta 1-antagonistic profile.

Selectivity of antagonist and partial agonist activity of celiprolol in normal subjects

1. The aims of this study were to assess the relative beta 1/beta 2 selectivity of the antagonist and partial agonist activity (PAA) of celiprolol in man. 2. Eight normal males received single oral doses of celiprolol 200 mg (C200), 400 mg (C400) and 800 mg (C800); atenolol 50 mg (A50), 100 mg (A100) and 200 mg (A200); nadolol 40 mg (N40) and placebo (PL), administered in a single-blind, randomised crossover design. 3. At rest, in the presence of low levels of circulating adrenaline and noradrenergic tone, a low dose of celiprolol (C200) showed evidence of beta 1-PAA by significant increases in systolic blood pressure and resting heart rate. At higher doses (C400, C800), beta 2-PAA became evident by a significant increase in postural finger tremor, whereas C200 had no effect. 4. In the presence of a beta 1-adrenoceptor agonist, as assessed by reduction of exercise tachycardia, increasing doses of celiprolol produced significantly less beta 1-adrenoceptor blockade compared with atenolol. Furthermore, there was no increase in beta 1-adrenoceptor blockade beyond C400. 5. In the presence of a beta 2-adrenoceptor agonist, as assessed by blunting of terbutaline-induced chronotropic, hypokalaemic and finger tremor responses, celiprolol exhibited less beta 2-adrenoceptor blockade than comparable doses of atenolol used in clinical practice. 6. Exercise hyperkalaemia was blunted significantly by C400 and C800 in comparison with all doses of atenolol and nadolol.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of beta blockade with (epanolol) and without (atenolol) intrinsic sympathomimetic activity in stable angina pectoris

Beta blockade constitutes efficient therapy for stable angina pectoris. The effects of lowering blood pressure and heart rate with such treatment are not always desired. Epanolol is a beta 1-selective partial agonist with minor effects on blood pressure and heart rate at rest. Atenolol is a pure beta 1-selective antagonist with more pronounced effects on blood pressure and heart rate at rest. The effects of epanolol, 200 mg o.d., and atenolol, 100 mg o.d., were compared in 173 middle-aged patients with stable angina pectoris in a randomized, double-blind, parallel group-controlled study for one year. No significant differences were shown in angina attack rate, nitrate consumption, or exercise performance. Resting heart rate and blood pressure were significantly lower on atenolol. Epanolol tended to be better tolerated than atenolol, as shown by visual analogue scales of well-being, activity, energy, and warm extremities, further supported by fewer reports on possible adverse reactions. In conclusion, epanolol appears to be as effective as atenolol and better tolerated in patients with stable angina pectoris.

Evaluation of in vivo partial beta 1/beta 2-agonist activity: a dose-ranging study with carteolol

1. The aims of this study were to investigate the partial agonist profile of carteolol and evaluate methodology for differentiating relative beta 1 and beta 2 partial agonist activity (PAA) in vivo. 2. Eight normal subjects received single oral doses of carteolol 10 mg, 30 mg and 60 mg; nadolol 40 mg; pindolol 30 mg and placebo, given in a single-blind, randomised crossover design. 3. beta 1-PAA was demonstrated with carteolol by dose-related increases in resting heart rate and systolic blood pressure, and a plateau in the dose-response curve for attenuation of exercise tachycardia. beta 2-PAA with carteolol was evidenced by a dose-related increase in resting finger tremor and progressive attenuation of exercise-induced hyperkalaemia. beta 2-adrenoceptor antagonism was shown by attenuation of terbutaline induced hypokalaemic, chronotropic and finger tremor responses. 4. Carteolol behaved as a non-selective beta-adrenoceptor antagonist with both beta 1 and beta 2-PAA components. In the standard clinical dose range of 10-30 mg, its in vivo PAA effects were relatively beta 1-selective. Thus at low doses, there appeared to be a dissociation between selectivity of antagonist and partial agonist activity. 5. Attenuation of exercise hyperkalaemia appears to be a novel and sensitive method for the evaluation of beta 2-PAA in vivo.

Pharmacokinetic and pharmacodynamic studies in man with an antianginal agent 'Visacor'

This randomized, double-blind, crossover study in 10 healthy male volunteers compared four single oral doses of ICI 141,292 ('Visacor'), i.e. 50, 100, 200, and 300 mg, with placebo. Venous blood samples were collected pre-dose and at various times after dosing and the concentrations of ICI 141,292 in the plasma were determined by radioimmunoassay. A standardized 4-min bicycle exercise test was also performed and before this the resting haemodynamic parameters were assessed. Peak plasma concentrations of ICI 141,292 and the area under the plasma concentration-time curve increased disproportionately with dose such that after scaling to a dose of 200 mg there remained a significant linear trend with dose. The time to peak plasma concentration displayed an increasing trend with dose and, once again, the linear component of this trend was statistically significant. The mean heart rates during exercise were all significantly reduced compared to placebo for 24 h by each of the doses (range 7.8 to 17.4 beats min-1 at 24 h, p less than 0.01). The increase in heart rate during exercise was inversely related to the logarithm of the ICI 141,292 plasma concentration with higher plasma concentrations being associated with lower heart rate increases. The mean supine resting heart rates were slightly but significantly reduced at 2 and 6 h after dosing by each treatment and by the 300 mg dose at 24 h. Each of the doses of ICI 141,292 was well tolerated.

Measurement and cardiovascular relevance of partial agonist activity (PAA) involving beta 1- and beta 2-adrenoceptors

In the normal heart the ratio of beta 1/beta 2-receptors in both atria and ventricles is about 75:25; in the failing heart the ratio is about 60:40. Stimulation of either beta 1- or beta 2-receptors results in a positive chronotropic and inotropic response. In the periphery, with the exception of lipolysis, renin release, control of intraocular pressure and intestinal relaxation, beta 2-related activity predominates. The nature of the beta 2-receptor is being unravelled and it has now been cloned. The beta-receptor antagonist is 'anchored' via disulfide bonding. Subsequent events involve the regulatory protein guanine nucleotide which couples the receptor to adenylate cyclase. beta-receptor density may by up- or down-regulated. beta-stimulation down-regulates (uncouples and internalizes or sequestrates) and beta-antagonism up-regulates beta-receptor numbers, but the functional implications of such changes are not always clear. A partial agonist occupies a receptor site and competitively inhibits the full agonist (e.g. noradrenaline). A partial agonist differs from a full agonist in that maximal response of a tissue is less. When background sympathetic activity is absent or very low a partial agonist will act as an agonist, e.g. increase heart rate, but when background tone is high the partial agonist will behave functionally as an antagonist, e.g. decrease heart rate. In animals partial agonist activity (PAA) can be assessed in many ways. In the catecholamine-depleted (reserpine or syrosingopine), vagotomized or pithed, intact animal beta-activity can be assessed via changes in heart rate, cardiac contractility and atrioventricular conduction. Isolated organs can also be used such as atria, papillary muscle, tracheal, mesenteric artery and uterine preparations. The choice of animal is important as marked species differences in response can occur. In man assessing PAA is difficult due to the presence of an intact sympathetic system: the problem can be overcome by autonomic blockade of constrictor and vagal reflexes with prazosin, clonidine and atropine but leaving the beta-receptor mediated responses unimpaired. beta 1- and beta 2-selective PAA can also be gauged via an increased sleeping heart rate (basal sympathetic tone) in the presence and absence of a beta 1- and beta 2-selective antagonist. beta 1-selective PAA can also cause an increase in resting systolic blood pressure, beta 2-selective PAA may be further assessed by a fall in DBP, increased blood flow, fall in peripheral resistance or increased finger tremor.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical pharmacology of epanolol. Pharmacodynamic aspects

Epanolol has been shown in animal models to be a selective beta-adrenoceptor partial agonist with agonist activity about 20 to 25% of that of the full agonist isoprenaline. Evidence is presented in this review supporting the conclusion that epanolol has the same pharmacological properties in man and that the agonist activity at the beta-adrenoceptor is less than the activity present in pindolol, but greater than that present in acebutolol. The pharmacodynamic consequences in man of the degree of agonist activity possessed by the beta 1-selective partial agonist epanolol include little reductions at rest in heart rate, blood pressure, various measures of cardiac haemodynamic parameters, peripheral blood flow and renal function. On exercise there is attenuation of the heart rate and systolic blood pressure responses, with less perceived exertion than with atenolol. Evidence is available which shows that attenuation of the tachycardia of exercise persists for 24 hours after a single dose of epanolol 200mg, a dose which retains selectivity for the beta 1-adrenoceptor. This pharmacological profile of epanolol in man suggests that it would be an effective antianginal agent when 200mg once daily is administered. Moreover, its unique profile (compared with other antianginal agents) may make it more tolerable to patients than existing antianginal therapy.