Intrinsic sympathomimetic activity: clinical fact or fiction?

Paradoxical and bidirectional drug effects

A paradoxical drug reaction constitutes an outcome that is opposite from the outcome that would be expected from the drug's known actions. There are three types: 1. A paradoxical response in a condition for which the drug is being explicitly prescribed. 2. Paradoxical precipitation of a condition for which the drug is indicated, when the drug is being used for an alternative indication. 3. Effects that are paradoxical in relation to an aspect of the pharmacology of the drug but unrelated to the usual indication. In bidirectional drug reactions, a drug may produce opposite effects, either in the same or different individuals, the effects usually being different from the expected beneficial effect. Paradoxical and bidirectional drug effects can sometimes be harnessed for benefit; some may be adverse. Such reactions arise in a wide variety of drug classes. Some are common; others are reported in single case reports. Paradoxical effects are often adverse, since they are opposite the direction of the expected effect. They may complicate the assessment of adverse drug reactions, pharmacovigilance, and clinical management. Bidirectional effects may be clinically useful or adverse. From a clinical toxicological perspective, altered pharmacokinetics or pharmacodynamics in overdose may exacerbate paradoxical and bidirectional effects. Certain antidotes have paradoxical attributes, complicating management. Apparent clinical paradoxical or bidirectional effects and reactions ensue when conflicts arise at different levels in self-regulating biological systems, as complexity increases from subcellular components, such as receptors, to cells, tissues, organs, and the whole individual. These may be incompletely understood. Mechanisms of such effects include different actions at the same receptor, owing to changes with time and downstream effects; stereochemical effects; multiple receptor targets with or without associated temporal effects; antibody-mediated reactions; three-dimensional architectural constraints; pharmacokinetic competing compartment effects; disruption and non-linear effects in oscillating systems, systemic overcompensation, and other higher-level feedback mechanisms and feedback response loops at multiple levels. Here we review and provide a compendium of multiple class effects and individual reactions, relevant mechanisms, and specific clinical toxicological considerations of antibiotics, immune modulators, antineoplastic drugs, and cardiovascular, CNS, dermal, endocrine, musculoskeletal, gastrointestinal, haematological, respiratory, and psychotropic agents.

A new water-soluble, selective beta-blocker with intrinsic sympathomimetic activity (ICI 141.292) in angina pectoris

In a placebo-controlled, randomized double-blind study the effect of ICI 141.292 (beta 1-selective beta-blocker with intrinsic sympathomimetic activity = ISA) was studied in 11 patients with severe angina pectoris. The doses used were 100, 200 and 300 mg once daily. The 24-hour heart rate was significantly reduced by all regimens, and the Holter-monitoring pattern indicated the presence of ISA-effect at least 20 hours after the 300-mg dose. Maximal heart rate and blood pressure were significantly reduced and exercise duration increased during a symptom-limited bicycle exercise test on 200 and 300 mg, but not on 100 mg daily. Resting heart rate and blood pressure were uninfluenced on all regimens. ICI 141.292 is an effective agent in patients with severe angina pectoris. The response pattern suggests the presence of clinically relevant ISA.

The pharmacologic treatment of uncomplicated arterial hypertension in patients with airway dysfunction

Because many antihypertensive drugs can affect airway function, the treatment of hypertension in patients with airway dysfunction is complex. For example, the worsening or precipitation of asthma by beta-adrenoceptor antagonists is well-recognized, but beta(1)-adrenoceptor blockers that exert mild beta(2)-agonist effects, and those that modulate the endogenous production of nitric oxide, affect airway function to a lesser extent. Therapy with selective alpha(1)-blockers is not contraindicated in cases of chronic airway obstruction. Conversely, alpha(2)-agonists must not be given to asthmatic subjects because they can adversely affect the bronchi. Calcium channel blockers do not exert severe side effects on the airways. Angiotensin-converting enzyme inhibitors may cause cough and exacerbate or even induce asthma; however, angiotensin II type I (AT(1)) antagonists do not cause cough. 5-Hydroxytryptamine modifiers such as urapidil are a treatment option for patients with chronic airway obstruction. In patients with airway dysfunction, we suggest treatment with thiazide diuretics as the initial drug choice, and calcium channel blockers if the response is poor. In the case of no response, calcium channel blockers alone must be used. However, there is no strict rule because individual patients may respond differently to individual drugs and drug combinations. Consequently, it is important to adopt a flexible approach. For patients who are unresponsive to the aforementioned drugs, AT(1) receptor antagonists, newer beta(1)-adrenoceptor-blocking agents with ancillary properties (eg, celiprolol or nebivolol), and/or vasodilators can be considered.

Do partial agonist beta-blockers have improved clinical utility?

Although beta-blockers were introduced into clinical medicine 30 thirty years ago, controversy continues as to the optimal pharmacodynamic profile of such agents. This commentary reviews the development of beta-blockers with partial agonist properties in the context of a recent study on epanolol. The influence of partial agonism on the efficacy and tolerability of beta-blockers is summarized, and it is concluded that, in general, there is little convincing evidence from controlled clinical studies that partial agonism confers significant clinical benefit over full antagonists.

Effects of carteolol on the electroretinogram in the perfused cat eye

Carteolol, a nonselective beta-antagonist, was administered intra-arterially in perfused cat eyes. Carteolol increased both photopic and scotopic electroretinogram b-wave amplitude dose-dependently and reversibly, but carteolol failed to induce significant changes in the flow rate of perfusate. This study suggests that carteolol may increase selectively the retinal perfusion flow rate, though it did not reflect the total perfusion flow, or carteolol may have an interaction with retinal beta-adrenergic receptors related to the origin of the b-wave. These ideas are supported by carteolol's intrinsic sympathomimetic activity and effects on endothelium of vessels.

Pharmacologic management of childhood hypertension

Antihypertensive drug therapy is used in children primarily to treat secondary forms of hypertension, because the prevalence of essential hypertension in the first decade of life is considerably less than 1% of the childhood population. This prevalence increases during the second decade of life, but the percentage of teenagers with essential hypertension continues to be low. Pharmaceutical companies have been able to target drug development to specific physiologic and biochemical systems. The converting enzyme inhibitors and calcium-channel blockers have greatly improved the success of therapy concomitant with a reduction in the incidence of adverse effects. The result has been a major change during the past decade in the recommendations for antihypertensive drug therapy.

Around the beta-blockers, one more time

We review the pharmacology, pharmacokinetics, and relative costs of beta-blockers, as well as indications for and therapeutic controversies surrounding their use. It is hoped that this discussion will assist clinicians in making informed decisions when choosing a drug for a hospital formulary or a particular patient. Beta-blockers are indicated for a variety of noncardiovascular and cardiovascular conditions, including hypertension, ischemic heart disease, arrhythmias, and prophylaxis of myocardial infarction (MI). These agents compete with catecholamines at beta-adrenoreceptors. They have different ancillary properties, including intrinsic sympathomimetic activity (ISA), cardioselectivity, and membrane stabilizing-activity, and vary in their duration of action, route of elimination, and lipophilicity. Beta-blocking agents decrease oxygen demand by exerting a negative inotropic and chronotropic effect. They also reduce blood pressure and possess antiarrhythmic effects. Beta-blockers penetrate the central nervous system (CNS) to different degrees and can cause a wide variety of CNS adverse effects. Nonselective beta-blockers have been noted to slightly reduce renal blood flow. Nadolol is an exception in that either no change, or even a small increase in renal blood flow, is observed upon initiation of therapy. Beta-blockers also act on the pulmonary bed by preventing beta 2-mediated bronchodilation, thereby exacerbating bronchospastic disease in some patients. Beta-adrenergic blocking agents can potentiate both hypoglycemia and hyperglycemia in diabetic patients. Their effects on total peripheral resistance (TPR) are controversial. Initially it appears that beta-blockade increases TPR. After chronic therapy, however, TPR decreases to or below baseline values. These agents appear to be equally efficacious in the treatment of hypertension, arrhythmias, and ischemic heart disease.(ABSTRACT TRUNCATED AT 250 WORDS)

The applied pharmacology of beta-adrenoceptor antagonists (beta blockers) in relation to clinical outcomes

Despite the fact that beta blockers were introduced into clinical practice 25 years ago, new beta blockers with differing kinetic and dynamic profiles continue to be developed and marketed. This overview assesses some of the more extensively studied agents from the point of view of proof of utility and the validity of claims for therapeutic advances. The clinical data suggests that despite the expectations of improvements based on kinetic and dynamic consideration, none of the newer agents have been shown unequivocally, either in terms of efficiency or tolerability, to be an advance over the reference agents, the beta 1 antagonists atenolol and metoprolol. This may be either because such improvements will not occur or because of shortcomings in the design and duration of comparative studies. There are trends to suggest that celiprolol has lesser effects on bronchial function and that it has a lesser impact on lipoprotein profiles. Approaches are suggested that might enable clinicians to appraise for themselves the validity of claims for the improved efficiency of new beta blockers.

[Changes in myocardial metabolism induced by drugs used during intensive care]

More and more patients with coronary heart disease (CAD) are admitted to intensive care units. The drugs used to treat these patients have various effects on the myocardium which must be known in order to avoid worsening the CAD. This review examines the metabolic effects on the myocardium of the most commonly used drugs in intensive care. The physiology of myocardial oxygen supply is first recalled with regard to the coronary circulation, myocardial oxygen extraction and consumption. Digitalis glycosides do not affect the coronary circulation, but the decrease myocardial oxygen consumption in patients with heart failure, mainly by lowering heart rate. Dihydropyridine calcium blockers (nifedipine, nicardipine) increase coronary blood flow, despite a decrease in arterial blood pressure. Their effects on myocardial oxygen consumption are mediated by a sympathetic reflex. Verapamil decreases the heart rate and myocardial inotropism, and is responsible for coronary vasodilation. The result is a decrease in myocardial oxygen consumption. Diltiazem and bepridil have almost similar effects: they decrease myocardial oxygen consumption and increase blood supply to the heart. It has been recently shown that verapamil was the most depressant calcium channel blocking agent, and that it resulted in the most important decrease in myocardial metabolism. Beta-blocking agents decrease myocardial metabolism, except those with an important intrinsic sympathomimetic activity, such as pindolol. Amiodarone can be considered as an alpha and beta blocking drug: its main effect is to counteract the effects of endogenous catecholamines on myocardial metabolism. The sympathomimetic amines (noradrenaline, adrenaline, isoprenaline, dopamine, dobutamine) increase, to different extents, myocardial oxygen consumption. Vasodilators, such as the nitrates or sodium nitroprusside, decrease cardiac filling pressures, and increase myocardial blood flow, thus lowering myocardial oxygen consumption. Phosphodiesterase inhibitors (amrinone, enoximone) have both an inotropic and a vasodilating effect. They decrease cardiac afterload, and increase blood supply to the myocardium; this compensates for the increase in myocardial oxygen consumption due to the increase in myocardial contractility. Because all the drugs used in intensive care have different effects on myocardial metabolism, their reasoned use should avoid an inappropriate increase in oxygen demand.

Beta-adrenergic blocking drugs in the treatment of congestive heart failure

Experimental and clinical data suggests that increased serum catecholamines may have predominantly detrimental effects in patients with congestive heart failure. Some investigators have proposed use of beta-blockers in heart failure as a means of ameliorating the harmful effects of the excess catecholamines. The clinical experience to date with use of these agents as therapy in congestive heart failure is limited but does suggest a future role for beta-blockers as adjunct therapy in a select population of patients with heart failure.

Optimal features of a new beta-blocker

Therapeutics involves the careful balance between treatment disadvantages and advantages--the so-called risk-benefit ratio. Even after 20 years beta-blockers must be selected carefully to suit the patient's needs. This review examines several problems associated with beta-blockade. Generally, beta1-cardioselectivity is considered advantageous, but properties such as partial agonist activity, which limits receptor up-regulation, might be of greater value in reducing the adverse effects associated with abrupt drug withdrawal. Beta-Blockers, either lipophilic or hydrophilic agents, have specific problems: lipophilic drugs provoke adverse central nervous system effects and need careful dose titration; variable gastrointestinal absorption is common with hydrophilic agents, whereas extra care is needed in patients with renal impairment. For most patients, especially those with asymptomatic conditions, once-daily dosing is preferred. For many, the quality of life is of overriding clinical importance. Despite significant pharmacokinetic and pharmacodynamic advances, the final criteria depend largely on a clinical assessment, improvement in the quality of life, and patient preference. We still await the discovery of an ideal beta-adrenoceptor blocking agent; some of the newer beta-blockers, however have many of the properties that clinicians value.

Preservation of the end-systolic pressure/end-systolic dimension relation following pindolol in congestive heart failure

Beta blockade may adversely affect inotropic state of the ventricle, resulting in exacerbation of congestive heart failure in subjects with reduced ventricular function. In normal subjects, ventricular contractility appears to be preserved following administration of beta blockers with intrinsic sympathomimetic activity (ISA). The inotropic state of the ventricle was assessed in seven subjects with congestive heart failure (mean ejection fraction = 23 +/- 5%) before and after administration of the ISA beta blocker, pindolol, with the use of the noninvasively derived end-systolic pressure/end-systolic dimension (ESP/ESD) relation. The mean slope of the ESP/ESD relation was 36.3 +/- 20.4 mm Hg/cm at baseline and increased to 45.0 +/- 25.2 mm Hg/cm following five consecutive 10 mg oral doses of pindolol (p = ns). Other simultaneously derived inotropic indices that included percent fractional shortening, mean delta P/delta T, velocity of circumferential fiber shortening, and preejection period-to-left ventricular ejection time ratio showed directionally similar changes toward a mild increase in contractility. These results indicate that the slope of the left ventricular ESP/ESD relation is not altered following repeated dosing with pindolol in subjects with congestive heart failure. This reflects a preservation of inotropic state following administration of this ISA beta blocker in a population with severely compromised ventricular function.

Evaluation of the antihypertensive effect of celiprolol by ambulatory blood pressure monitoring

The use of ambulatory blood pressure monitoring has gained popularity because it is not subject to those limitations associated with traditional sphygmomanometry (inaccuracy of blood pressure readings, low number of readings, and failure to represent daytime blood pressure readings). In the present study, we provide evidence that the 24-hour mean blood pressure obtained through intraarterial blood pressure measurements in ambulatory patients provides a more accurate diagnosis (and perhaps a prognosis) of hypertension than that provided by cuff-obtained casual blood pressure measurement. Furthermore, despite a reduction in the amount and in the accuracy of the information obtained, blood pressure data provided by noninvasive blood pressure monitoring are also more accurate diagnostically than cuff-obtained casual blood pressure measurements. In 15 essential hypertensive patients in whom celiprolol, 400 mg once daily, was compared with placebo in a randomized double-blind crossover study, the use of noninvasive 24-hour automatic blood pressure monitoring showed that in responsive patients, celiprolol induced a sustained reduction in systolic and diastolic blood pressure throughout the 24 hours. The blood pressure reduction was also apparent during the night, despite the concomitant occurrence of a slight tachycardia. These findings demonstrate that once-daily administration of celiprolol provides an effective lowering of the 24-hour blood pressure profile. This dosing schedule can therefore be regarded as appropriate for antihypertensive therapy.

Effects of three beta-blockers with different pharmacodynamic properties on platelet aggregation and platelet and plasma cyclic AMP

The effects of three different types of beta-adrenoceptor blocking agents on platelet aggregation and on platelet and plasma cyclic AMP content have been studied in 14 patients with mild hypertension given each drug in turn for two weeks. The drugs were a non-selective blocking agent with high intrinsic sympathomimetic activity, pindolol, the nonspecific blocking agent propranolol, and the beta 1-selective metoprolol. The threshold values of ADP and adrenaline for irreversible platelet aggregation were significantly higher for pindolol and metoprolol than for propranolol. The cyclic AMP content of platelets was higher during pindolol and metoprolol than during propranolol treatment. Pindolol produced a substantial increase in plasma cyclic AMP relative to the other two drugs. Thus, platelet aggregation and cyclic AMP formation are influenced by beta-adrenoceptor blockade in proportion to intrinsic sympathomimetic activity and affinity for different beta-adrenoceptor subtypes.

Effect of beta blockers on vascular resistance in systemic hypertension

Over 20 years ago, it was established that beta blockers could reduce high blood pressure. Currently, several beta blockers with different ancillary properties are available. They all have the property of blocking beta 1 receptors but differ from each other in a number of other respects: they may or may not block beta 2 receptors in low doses (beta 1 = receptor selectivity); they may or may not possess varying degrees of partial agonist activity, also known as intrinsic sympathomimetic activity (ISA); they vary in the extent to which they are soluble in fat (lipophilicity). A review of relevant published findings indicates that the effects of beta blockers on cardiac output are not essential for their antihypertensive effect, nor is penetration of these drugs into the brain and cerebrospinal fluid. Reduction in blood pressure during long-term beta blocker therapy is always associated with reduction of total peripheral resistance. Beta blockers with sufficient ISA to prevent cardio-depression, by exerting less negative inotropic and chronotropic effects on the heart, do not cause initial reflex vasoconstriction in response to cardiac beta blockade. Unlike beta blockers devoid of ISA, these agents ultimately reduce blood pressure by lowering the increased vascular resistance in hypertension to below pretreatment values. Recent beta blocker research has revealed a number of ways to manipulate the characteristically elevated vascular resistance in hypertension. Examples of these efforts are the combination of ISA, alpha 1 or alpha 2 receptor blockade and direct vasodilating properties in the enantiomers of a single beta blocker molecule. The practical significance of these developments remains to be established.

Hemodynamic-inotropic response to beta-blocker with intrinsic sympathomimetic activity in patients with congestive cardiomyopathy

The rest and exercise hemodynamic-inotropic response to administration of the beta-blocker pindolol was evaluated in 10 patients with congestive cardiomyopathy to determine whether the intrinsic sympathomimetic activity (ISA) of this agent may preserve ventricular function in the setting of beta-blockade. A significant (p less than .05) rise in systemic and pulmonary vascular resistance and a decline in stroke volume and cardiac index was observed after a single 10 mg dose. The change in cardiac index was negatively correlated with free drug concentration (r = -.59, p less than .01); the change in pulmonary and systemic vascular resistance showed a positive correlation with plasma concentration (r = .67, r = .57, respectively; all p less than .05). The response to exercise reflected a predominant beta-blocking effect, with a significant decrease in peak heart rate and cardiac index and an increase in pulmonary vascular resistance. There were no significant changes in variables of right or left ventricular inotropy after administration of the drug. The mean baseline plasma norepinephrine concentration for the population was 609 +/- 172 pg/ml (normal = 196 +/- 7 pg/ml) and was markedly elevated in two patients (931 and 2053 pg/ml) who developed severe pindolol-induced hypotension. Renin increased markedly in these two patients, but decreased in each of the remaining eight patients. These data indicate that although inotropy is not adversely affected by pindolol, increased afterload, which appears to be mediated by peripheral beta-blockade, results in a reduction in ventricular performance.(ABSTRACT TRUNCATED AT 250 WORDS)

A trial of the calcium antagonist nisoldipine in hypertensive non-insulin-dependent diabetic patients

The antihypertensive and metabolic effects of a new calcium antagonist nisoldipine (10 to 20 mg at night) were investigated in 14 mild to moderately hypertensive non-insulin-dependent diabetic patients (median age 62, range 50-70 years). In a 12-week placebo controlled single blind study, sitting and standing blood pressure were significantly lowered (p less than 0.001). Heart rate was unchanged as were blood urea, creatinine, bilirubin, mmol/l (mean +/- SEM) and uric acid concentrations. Plasma sodium levels fell during active therapy (142 +/- 0.5 mmol/l (mean +/- SEM) versus 139 +/- 0.5 (p less than 0.001) and remained lower during the washout period. Plasma calcium concentrations increased during nisoldipine therapy (2.41 +/- 0.02 versus 2.51 +/- 0.03 mmol/l, p less than 0.001) and returned towards baseline during the washout period. Plasma ionized calcium concentrations showed similar changes but plasma sodium and calcium remained within the normal laboratory ranges in all patients at all times. Serum triglyceride concentrations fell (placebo 1.9 +/- 0.02 mmol/l vs nisoldipine 1.6 +/- 0.2, p less than 0.05), but fasting cholesterol was unchanged. Fasting blood glucose, and the blood glucose response to oral glucose challenge (75 g) showed no differences though HbA1 concentrations fell (10.6 +/- 0.7 versus 9.2 +/- 0.05%, p less than 0.05) and tended to rise when the drug was withdrawn. Haemoglobin concentrations also fell during active therapy (14.7 +/- 0.4 vs 14 +/- 0.32 g/dl p less than 0.001) and also remained lower after the washout period (13.9 +/- 0.03 g/dl).(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-blockers in congestive cardiomyopathy. Conceptual advance or contraindication?

The precise role of adrenergic activity in congestive cardiomyopathy has not been established. A number of mechanisms through which increased catecholamine levels may be harmful, along with the clinical and experimental evidence supporting this concept, are summarized in this review. In this context, the suggestion that beta blockers may be beneficial for patients with severe heart failure, despite their well-known propensity to decrease cardiac contractility, can be better understood. Published reports on the use of beta blocker therapy for congestive cardiomyopathy now include approximately 200 patients, but have yielded inconsistent results. Non-randomized trials in Sweden have suggested increased survival, with most patients having improved functional status while receiving beta blockade, although improvement may take three to six months to become evident. The Swedish group also reported clinical deterioration after discontinuation of beta blockade. Two recent randomized trials in America yielded promising results, but the unexpectedly low mortality in the placebo groups emphasizes the critical importance of concurrent controls. Unfavorable reports have involved small groups with short-duration therapy. Even in these reports, overt aggravation of clinical heart failure has been quite infrequent but sometimes profound. As large scale trials are undertaken, an obvious goal is the development of methods to differentiate the patients with congestive cardiomyopathy who will benefit in response to beta blocker therapy from the few patients who will have a serious adverse response.

Treatment of hypertension in the elderly

Investigation of preventive measures for hypertension and atherosclerosis is a geriatric medicine priority. While the causes of both isolated systolic hypertension and conventional systolic and diastolic hypertension in the elderly are well defined, the benefits of lowering blood pressure are not. Evidence to support the treatment of symptomatic hypertension is convincing for men 60 years of age; it is not for women in this age group. The need to treat hypertension, particularly isolated systolic hypertension in patients above 75 years old, is still not resolved. Isolated systolic hypertension in older patients is at least as strong a risk factor for cardiovascular disease as is diastolic hypertension. Ongoing trials may answer these questions; in the meantime, drug therapy in this group will vary widely. The elderly hypertensive is more likely than the younger hypertensive to have other diseases; diagnosis of these disorders is crucial. Hypertension arising de novo late in life warrants a search for underlying and possibly remedial causes. Antihypertensive drug therapy to relieve symptoms is difficult to justify, because most elderly hypertensive patients are asymptomatic; however, it has been shown to delay morbid and fatal complications of hypertension. Appropriate therapy for the elderly hypertensive must be individualized and should be associated with few or no side effects. The thiazides are the preferred diuretics for long-term treatment of hypertension in the elderly. Beta blockers are attractive because they are cardioprotective, counter the end organ effect of catecholamines and reduce angina; however, some decrease cardiac output, increase peripheral resistance, decrease renal blood flow and cause fatigue.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative study of the respiratory effects of two beta 1-selective blocking agents atenolol and bevantolol in asthmatic patients

Seven asthmatic patients were given a single placebo tablet in a first test session and then in two subsequent double blind sessions they randomly received 400 mg bevantolol or 100 mg atenolol, with at least 2 days between each of the sessions. Neither beta-blocker had any significant effect on FVC as compared to the placebo. FEV 1, however, was significantly lower 2 and 3 h after atenolol or bevantolol; there was no significant difference between the effects of the two drugs on FEV 1. Peak expiratory flow rate was reduced by bevantolol but not by atenolol, the difference reaching significance after 3 h. Fenoterol inhalation at the end of each test session always enhanced pulmonary performance, but to a lesser extent after bevantolol than after placebo or atenolol. A slower heart rate was recorded 2, 3, and 4 h after bevantolol and 3 and 4 h after atenolol; the mean 2-h value was significantly lower with atenolol than with bevantolol. No patient suffered any adverse effect. Bevantolol may be slightly less selective than atenolol.

Effect of selective and nonselective beta-adrenoceptor blockade on thermoregulation during prolonged exercise in heat

The effect of selective and nonselective beta-adrenoceptor blockade on the thermoregulatory responses of 11 physically active, healthy, young adult men was studied during 2-hour block-stepping in heat. The trial consisted of 3 periods of 6 days each during which propranolol (160 mg/day), atenolol (100 mg) or matching placebo was administered in a randomized, double-blind crossover fashion. Propranolol and atenolol induced similar, significant (p less than 0.001) increases in subjective ratings of perceived exertion. The mechanism of this increased fatigue was not evident from the documented alterations in serum electrolyte, blood glucose and blood lactate levels or ventilatory parameters. Propranolol did, however, induce a postexercise delayed serum-potassium reversion. Although rectal and mean skin temperature responses were essentially unaltered by beta-adrenoceptor blockade during block-stepping, an increased total sweat loss was observed with propranolol (p less than 0.01 versus placebo) and to a lesser degree with atenolol (p = not significant versus placebo). This indicates that persons receiving beta-adrenoceptor blockers have an increased need to adhere to a strict fluid-replacement regimen during exercise. This potentially adverse response was minimal with atenolol in contrast to propranolol, and this in turn suggests the use of beta1-selective adrenoceptor blockers during prolonged exercise when adequate fluid replacement is not possible.

Exercise and hypertension

Hypertension is a major risk factor for atherosclerosis. In this article the authors review the use of physical activity as therapy for elevated blood pressure and explore the hemodynamic effects of exercise among patients with treated and untreated hypertension. Recommendations concerning the use of exercise in the management of hypertension are outlined.

Mechanisms of action and the clinical pharmacology of beta-adrenergic blocking drugs

At present more than 20 beta-adrenergic blocking drugs are commercially available in Western Europe, and six are available in the United States. The clinical indications for their usage include hypertension, arrhythmias, ischemic heart disease, thyrotoxicosis, migraine headaches, glaucoma, and anxiety states. We will review the mechanisms suggested for the antihypertensive action of beta-adrenergic blocking drugs as well as these agents' clinical pharmacologic aspects. In general, the pharmacodynamic effects of the beta blocking drugs are quite similar, yet the properties of biotransformation, including pharmacokinetics, tend to be distinguishing features.

Management of patients with hypertension and angina pectoris

Management of patients with concomitant hypertension and angina pectoris mandates that the physician pay attention to the underlying pathophysiology. The heart, when exposed to years of hypertension, becomes "remodeled." Overall mass is enlarged, the walls are thickened, and initial cavity volume remains normal or relatively small. Left ventricular end-diastolic pressure rises in the setting of a hypertrophic noncompliant ventricle; coronary resistance and coronary perfusion pressure are increased; and coronary vascular reserve, even with widely patent coronary arteries, is decreased. Long-standing hypertension--a risk factor for coronary atherosclerosis--is often accompanied by epicardial coronary stenoses that aggravate these coronary abnormalities. In managing the patient with hypertension and angina pectoris, it is important to determine whether the angina occurs in the setting of hypertensive hypertrophic disease alone or coexists with coronary arterial stenoses. Also important to therapy is whether the ventricle is of normal size with good function or decompensated with dilatation and diminished function. The latter two anatomic considerations, namely, epicardial coronary patency and left ventricular cavity size, will influence the choice of an anti-ischemic regimen. For example, diuretic and nitrate therapy can be hazardous, and digitalis unnecessary, in the setting of a nondilated hypertrophic ventricle with hyperdynamic function. On the other hand, the combined use of beta blocking agents plus calcium antagonists is particularly effective in lowering blood pressure and in improving coronary blood flow. Finally, this combination has been shown to be rapidly effective and to have prolonged benefit in this setting. The choice of these latter agents is also affected by the underlying state of the ventricle. Calcium channel blocking agents without significant negative inotropic effect, such as nifedipine and nitrendipine, would be suitable in patients with decompensated ventricular function and dilated left ventricular cavities. Both of these drugs have been shown to increase cardiac output and contractility via a reflex effect and to have little or no direct negative inotropic effect. In contrast, verapamil has a direct negative inotropic effect. The final choice of agents must be tailored to the needs of the individual patient, and the physician also has to determine the role of specific agents in the natural history of hypertensive heart disease.

Oxprenolol in clinical practice

Oxprenolol is a potent noncardioselective beta-adrenoceptor blocking drug with partial agonist activity of proved efficacy and high tolerability in patients at risk of various cardiovascular disease syndromes. The drug rapidly relieves angina and attenuates the electrocardiographic evidence of myocardial ischemia. It is a potent antihypertensive drug that not only reduces the blood pressure at rest but also prevents the surges associated with exercise and psychic stress. Oxprenolol has substantial benefit in the alleviation of many of the somatic sequelae of psychic stress and anxiety. The drug also suppresses the cardiovascular and metabolic effects of cigarette smoking. In the field of primary prevention, oxprenolol has attributes that could be expected to reduce the long-term cardiovascular complications of high blood pressure. In the secondary prevention, it reduces the further incidence of sudden death in patients in whom administration is started in relatively small doses within a few weeks after acute myocardial infarction. In the 15 years that the drug has been available for clinical prescription, it has established a reputation for high clinical tolerability.

Oxprenolol in the treatment of hypertension in the elderly

Controversy continues to surround the value of drug treatment of hypertension in the elderly. Epidemiologic evidence implicates hypertension as a major risk factor in the precocious development of stroke and coronary heart disease in the elderly subject as clearly as it is implicated in the younger person. The hemodynamic and neuroendocrine profiles of the older patient with essential hypertension are similar to those of younger patients in the stable phase of the disease. However, the arterial ravages induced by many years of sustained hypertension render the circulation of the elderly subject more sensitive to pharmacologic intervention. The benefit-risk ratio of most antihypertensive drugs appears to be inversely related to age. Diuretics reduce the blood pressure at rest but have no influence on the increases in systolic pressure during normal activity; in addition, they carry potentially serious metabolic hazards in the elderly hypertensive patient. Centrally acting drugs likewise lower the blood pressure at rest without influencing the high systolic pressures induced by exercise. They also enhance the tendency to endogenous depression. Adrenergic-neurone blocking drugs and alpha-adrenoceptor antagonists are contraindicated because of the frequency of impaired cardiovascular reflexes in the elderly. The beta-blocking drugs can reduce the risk of coronary and cerebrovascular disease in the older patient with hypertension. They appear to be well tolerated, but because of their impaired metabolic handling in many elderly patients they should probably be used in smaller doses than those prescribed in younger patients. The influence of antihypertensive treatment on cardiovascular morbidity and mortality in the elderly hypertensive patient is not known.