Initial clinical experience with ICI 141,292 (Visacor), a new selective beta 1-adrenoceptor blocker with ISA--a multicentre trial in 59 patients

Modest antihypertensive effect of epanolol, a beta 1-selective receptor blocker with beta 1 agonist activity: an acute and long-term hemodynamic study at rest and during exercise and double crossover comparison with atenolol on ambulatory blood pressure

Beta-blockers with less cardiodepressive effect than traditional nonselective beta(1+2)-blocking agents could be useful in the treatment of hypertension, provided the reduction in blood pressure was satisfactory. Epanolol, a selective beta 1-receptor blocker with intrinsic sympathomimetic activity, induced a fall in intraarterial pressure of 8% at rest sitting and 11% during 100 W bicycle exercise after the first dose of 200 mg in 12 patients with essential hypertension. Heart rate, stroke index, and cardiac index initially fell by 14%, 11%, and 23%, respectively. The total peripheral resistance index increased by 21% after 2 hours, and then reverted towards the pretreatment level. After 10 months of epanolol treatment (mean 300 mg/day), the reduction in arterial pressure was 5% at rest and 10% during exercise. Cardiac index and heart rate were still reduced 14-21%, while total peripheral resistance was unchanged or slightly increased (2-10%). Twenty-four hour ambulatory blood pressure was higher on epanolol (300 mg/day) than on atenolol (150 mg/day) treatment (137/97 vs. 128/91 mmHg). Thus, the achieved blood pressure reduction induced by epanolol was moderate, while other characteristics of beta-receptor blockade, in particular, the reduction of heart rate and cardiac output, were maintained. This suggests that the compound may be useful for other cardiovascular disorders, e.g., angina pectoris in patients without hypertension or cardiac arrhythmia.

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.

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.

Epanolol. A new once-daily antianginal agent: dose finding and long term efficacy

Epanolol is a new once-daily agent for the treatment of angina pectoris. This study was conducted in 2 parts. Firstly, a dose-finding study was performed using placebo and epanolol 100, 200, 300 and 400mg to assess the efficacy and safety of the drug. Once-daily epanolol 200mg was an effective dose, significantly reducing angina attack rate and increasing exercise duration and work output. At the same time, an improvement was noted in the patients' well-being and their ability to undertake normal daily activities. The 200mg dose regimen was used in a long term (12 months) assessment of the efficacy and safety of epanolol in the second part of this study. The efficacy of epanolol was clearly maintained throughout the full treatment period without adverse events or withdrawals as a result of treatment. The effectiveness and safety of epanolol are attributed to its selective beta 1-partial agonist activity. At rest, the degree of agonist activity (about 20% of that of isoprenaline) may prevent some of the untoward effects occasionally seen with full beta-blockers. During exercise, the antagonist activity becomes apparent and cardiac ischaemia is reduced.

The effect of epanolol on intra-arterial ambulatory blood pressure and baroreceptor heart rate reflex in essential hypertension

1. The effect of chronic treatment with epanolol, a new cardioselective beta-adrenoreceptor antagonist with moderate beta 1-selective intrinsic sympathomimetic activity (ISA), on 24 h ambulatory intra-arterial blood pressure (24 h IABP) and the sino-aortic baroreceptor heart rate (SAB/HR) reflex was investigated in six hypertensive subjects. 2. All subjects demonstrated a greater than 10% reduction in mean arterial pressure with atenolol therapy (100 mg once daily) before entering a randomized, double-blind, placebo-controlled, crossover protocol with epanolol (100 mg twice daily for 4 weeks). 3. Epanolol treatment at this dose was not associated with significant reduction in systolic or diastolic 24 h IABP or heart rate. There was no change in SAB/HR reflex set point, sensitivity or latency with epanolol. 4. beta 1-selective ISA may be undesirable in beta-adrenoceptor antagonists used to treat hypertension.

Post-exercise hypotension: the effects of epanolol or atenolol on some hormonal and cardiovascular variables in hypertensive men

1 Eight men with primary hypertension were treated for 3 weeks with placebo, epanolol (200 mg or 400 mg), or atenolol 100 mg in a randomised cross-over study. Each active treatment period was preceded by a 3 week placebo treatment period and both investigators and subjects were blind to the active drug sequence. 2 At the end of each period, measurements were made of resting cardiovascular (heart rate, blood pressure, forearm blood flow) and biochemical variables (plasma renin, angiotensin II, aldosterone, adrenaline, noradrenaline, vasopressin, sodium and potassium concentrations and osmolality). Responses to exercise (including gas exchange, sweat rate, and ratings of perceived exertion) and the reflex cardiovascular adjustments to distal body subatmospheric pressure were also assessed. 3 The reduction of exercise-induced tachycardia by epanolol 400 mg was comparable to that of atenolol. There was very little difference in the effects of atenolol or epanolol 400 mg on resting blood pressure, but in both cases blood pressures were usually significantly lower than with epanolol 200 mg. 4 Although each active treatment influenced the renin-angiotensin system and circulating levels of catecholamines, the exercise-induced reduction in blood pressure was unaffected. Thus, the hypotensive effects of pharmacological and non-pharmacological interventions were additive.

Is the ISA of pindolol beta 2-adrenoceptor selective?

1. Pindolol is a beta-adrenoceptor blocking drug with ISA (also called partial agonist activity). This means that in addition to blocking the effects of beta-adrenoceptor agonists, it produces some stimulation of beta-adrenoceptors. 2. In vitro studies with pindolol show that its maximum stimulant action is similar to that of isoprenaline in tissues possessing mainly beta 2-adrenoceptors, but is negligible in tissues possessing mainly beta 1-adrenoceptors. This suggests selective stimulation of beta 2-adrenoceptors. 3. In man the arteriodilator effects observed after intra-arterially infused pindolol at concentrations within the same range as those producing an antihypertensive effect also suggest a stimulant action on vascular beta 2-adrenoceptors. 4. The fact that pindolol prevents the reduction of resting heart rate and cardiac output observed after drugs lacking ISA at first sight suggests stimulation of cardiac beta 1-adrenoceptors. However, human atria possess not only beta 1- but also beta 2-adrenoceptors, stimulation of which would produce the same effect. 5. Although all beta-adrenoceptor antagonists lower blood pressure, recent experiments have shown that those agents with combined beta 1-adrenoceptor blocking activity and ISA at those receptors are less effective. This observation lends weight to the thesis that pindolol does not stimulate beta 1-adrenoceptors since it lowers blood pressure as effectively as drugs lacking ISA. 6. The evidence available therefore suggests that although pindolol blocks both beta 1- and beta 2-subtypes, it selectively stimulates beta 2-adrenoceptors.

Ro 31-1118, a new cardioselective beta-adrenoceptor antagonist. Pharmacokinetics and effects on heart rate and blood pressure in mild hypertensives

Five patients with mild hypertension were given single oral doses of Ro 31-1118 (10,20,40, and 80 mg) and placebo in a randomized, double-blind, within-patient study. Plasma concentrations of Ro 31-1118 and supine, standing, exercise, and post-exercise heart rates and blood pressures were measured before and at regular intervals after drug administration. The pharmacokinetic data were consistent with a one-compartment model with first-order absorption and a variable time lag. Peak plasma concentrations and area under curve were linearly related to dose, whereas time to peak concentration, half-time, clearance and apparent volume of distribution were dose-independent. There was a reduction in exercise and post-exercise heart rate of approximately 10% after 10 mg and 20 mg Ro 31-1118, and of approximately 15% after 40 mg and 80 mg. At all doses standing systolic blood pressure was reduced by approximately 5%. A similar fall was seen in exercise and post-exercise systolic blood pressures. There was no substantial effect of Ro 31-1118 on supine or standing heart rates nor on diastolic blood pressure. No adverse effects were reported. It is concluded that Ro 31-1118 has linear pharmacokinetics over the dose range 10-80 mg, and has a weak antihypertensive effect when administered in single doses to patients with mild hypertension.