How intrinsic sympathomimetic activity modulates the haemodynamic responses to beta-adrenoceptor antagonists. A clue to the nature of their antihypertensive mechanism

Sex-dependent changes in physical, mental, and quality of life outcomes in metoprolol-treated Chinese chronic heart failure patients

This study assessed sex differences in cardiac and motor functions, quality of life (QoL), and mental status in Chinese chronic heart failure (CHF) patients after metoprolol treatment.This single-center prospective study, conducted from February 2013 to April 2016, included CHF patients (men and women) with resting heart rate (HR) >80 beats/min using metoprolol continuous release tablets. Metoprolol-induced changes in cardiac and motor functions, QoL, and mental status at 1, 3, 6, 9, and 12 months from baseline, within and between the sexes, were analyzed. Descriptive data were represented as counts, percentages, and mean ± standard deviation. Differences at various follow-up periods were compared using repeated measures one-way analysis of variance, followed by post hoc Dunnett's multiple comparison test. Statistical significance was considered at P < .05.Compared with men, women reported significantly higher systolic blood pressure (SBP) (122.28 ± 6.76 vs 125.47 ± 6.67 mm Hg, P < .05) and Veterans Specific Activity Questionnaire score (8.16 ± 0.98 vs 8.47 ± 0.89, P = .05) at 12 months. Men reported higher Hospital Anxiety and Depression Scale scores for depression than women at 1 month (10.27 vs 8.83, P < .05) and for anxiety at 12 months (8.4 vs 7.72, P < .05). Metoprolol significantly decreased HR and Minnesota Living with Heart Failure Questionnaire score in men (64.5 ± 3.13 and 53.7 ± 8.00) and women (65.38 ± 3.32 and 53.85 ± 8.42, respectively). Ejection fraction (%, men: 50.00 ± 4.45, women: 50.72 ± 4.09), cardiac index (L/min/m, men: 2.70 ± 0.25, women: 2.78 ± 0.23), 6-minute walk test distance (m, men: 414.41 ± 20.84, women: 420.34 ± 20.35), and short form-8 questionnaire scores (men: 52.05 ± 1.94, women: 52.19 ± 2.58) increased significantly in both the sexes (P < .001 for all) at 12 months. Copenhagen Burnout Inventory score significantly increased in men (mean score 62.43, P < .05).Metoprolol treatment improves cardiac and motor functions, QoL, and anxiety scores but causes greater depression and burnout in men and women. Sex was seen to affect mental status of CHF patients the most.

Enhancement in Corneal Permeability of Dissolved Carteolol by Its Combination with Magnesium Hydroxide Nanoparticles

We prepared magnesium hydroxide (MH) nanoparticles, and investigated their effect when combined with dissolved carteolol on the bioavailability and intraocular pressure (IOP)-reducing effect of carteolol. The carteolol was solved in saline containing additives (0.5% methylcellulose, 0.001% benzalkonium chloride, 0.5% mannitol; CRT-solution). MH nanoparticles were prepared by a bead mill method with additives. Then carteolol/MH microparticle and carteolol/MH nanoparticle fixed combinations (mCMFC and nCMFC) were prepared by mixing the CRT-solution and MH particles. The transcorneal penetration and IOP-reducing effect of carteolol was evaluated in rabbits. The mean particle size of mCMFC was 7.2 μm, and the particle size was reduced to 73.5–113.5 nm by the bead mill treatment. The MH particles in nCMFC remained in the nano size range for 8 days after preparation, and the amounts of lacrimal fluid and corneal damage were unchanged by repetitive instillation of nCMFC (twice a day for 4 weeks). The transcorneal penetration of carteolol was enhanced by the combination with MH nanoparticles, and the IOP-reducing effect of nCMFC was significantly higher than that of CRT-solution or mCMFC. In conclusion, we designed nCMFC, and showed that the high levels of dissolved carteolol can be delivered into the aqueous humor by the instillation of nCMFC. Combination with MH nanoparticles may achieve an enhancement of corneal penetration for water-soluble drugs. These findings provide significant information that can be used to design further studies aimed at developing anti-glaucoma eye drugs.

Effects of selective β1-adrenoceptor blockade on cardiovascular and renal function and circulating cytokines in ovine hyperdynamic sepsis

Introduction

Activation of the sympathetic nervous system has beneficial cardiovascular effects in sepsis, but there is also evidence that sympatholytics have beneficial actions in sepsis. We therefore determined the effect of selective β₁-adrenoceptor blockade on cardiac and renal function and cytokine release in ovine hyperdynamic sepsis.

Methods

Hyperdynamic sepsis was induced by infusion of live E. coli for 24 hours in nine conscious sheep instrumented with flow probes on the pulmonary and left renal artery. Cardiovascular and renal function and levels of plasma cytokines were determined in a control group and during selective β1-adrenoceptor blockade with atenolol (10 mg intravenous bolus then 0.125 mg/kg/h) from 8 to 24 hours of sepsis.

Results

Hyperdynamic sepsis was characterized by hypotension with increases in cardiac output (CO), heart rate (HR) and renal blood flow (RBF), and acute kidney injury. Atenolol caused sustained reductions in HR (P <0.001) and CO (P <0.001). Despite the lower CO the sepsis-induced fall in mean arterial pressure (MAP) was similar in both groups. The sepsis-induced increase in RBF, decrease in renal function and increase in arterial lactate were unaffected by atenolol. Sepsis increased plasma levels of tumour necrosis factor alpha (TNF-α), interleukin 6 (IL-6) and IL-10. Atenolol caused a further increase in IL-10, but did not affect levels of TNF-α or IL-6.

Conclusions

In sepsis, selective β₁-adrenoceptor blockade reduced CO, but not MAP. During sepsis, atenolol did not alter the development of acute kidney injury or the levels of pro-inflammatory cytokines, but enhanced the release of IL-10. Atenolol appears safe in sepsis, has no deleterious cardiovascular or renal effects, and has an anti-inflammatory effect.

Effects of antiglaucoma drugs on blood flow of optic nerve heads and related structures

An association between glaucoma development or progression and compromised ocular blood flow has been postulated as a result of population-based studies and prospective cohort studies. Blood flow in the optic nerve head (ONH) is of primary importance in the pathogenesis of glaucoma. The potential to modify the blood flow in the ONH and its related structures has been reported in various agents, including topical antiglaucoma drugs and systemic drugs such as calcium channel antagonists, which are reviewed in this manuscript. Clinical implications of the improvement in ocular blood flow on the treatment of glaucomatous optic neuropathy require further investigation.

Changes in optic nerve head blood flow induced by the combined therapy of latanoprost and beta blockers

PURPOSE

To assess the effects of combined therapy with latanoprost and beta blockers on optic nerve head (ONH) blood flow in normal-tension glaucoma (NTG) patients.

METHODS

Intraocular pressure (IOP), ONH blood flow (laser speckle flowgraphy) and blood pressure were measured in 15 eyes of 15 NTG patients (41-76 years old) before treatment or after a 1-month washout period. Similar measurements were performed at 2 months after the commencement of treatment with latanoprost and at 3 months after the start of combined therapy of latanoprost with 0.5% timolol or 2% carteolol in a crossover study using the envelope method. Measurement was carried out 2-3 hr after the morning application of eyedrops.

RESULTS

Latanoprost decreased IOP with no significant change in ONH blood flow. Concomitant use of timolol or carteolol further decreased IOP with no significant difference between these two drugs. Only the combined therapy of latanoprost with carteolol significantly (p < 0.01) increased ONH blood flow by approximately 10%, compared to initial levels. There was no significant change in mean blood pressure, ocular perfusion pressure or pulse rate as a result of these therapies.

CONCLUSION

Topical latanoprost-carteolol combined therapy increased ONH blood flow in NTG patients, unlike latanoprost-timolol therapy. Because ocular perfusion pressure was unchanged, direct vasodilative effects were suspected as the mechanism.

Effects of topical adrenergic agents on tissue circulation in rabbit and human optic nerve head evaluated with laser speckle tissue circulation analyzer

The effects of topical adrenergic agents on the tissue circulation of the optic nerve head (ONH) were studied in animal and human eyes with use of a laser speckle tissue circulation analyzer. Drugs studied were nipradilol, a beta1-2-blocker with weak alpha-blocking and nitroglycerinlike activities; bunazosin, a selective alpha1-blocker; carteolol, a beta1-2-blocker with intrinsic sympathomimetic activity; and betaxolol, a selective beta1-blocker. In the animal experiment, one eye each of nine albino rabbits received 0.25% nipradilol (N = 9) twice daily for 15 days or 0.01% bunazosin (N = 10) twice daily for 20 days; the fellow eye received the vehicle of each drug in a randomized masked design. Normalized blur (NB) in an area of ONH free of visible surface vessels, a quantitative index of peripheral blood velocity in ONH, was measured under general anesthesia before treatment and 2 hours after the last instillation on the 15th or 20th day. At 15 days, intraocular pressure and NB in the nipradilol-treated eyes decreased by 4.3 mm Hg (P < 0.01) and increased by 15.9% (P < 0.01), respectively, while those in the vehicle-treated eyes showed little change. At 20 days NB in both bunazosin- and vehicle-treated eyes showed little change, while intraocular pressure decreased only in the bunazosin-treated eyes (P < 0.01). In the human volunteer experiment NB was averaged over five pulses (mean NB) in both eyes before and 1.5, 3.0 and 4.5 hours after a 30 microL instillation of the vehicle of carteolol or betaxolol to serve as a control. Intraocular pressure, blood pressure and pulse rate were also measured. One week later a 30 microL drop of 2.0% carteolol (N = 6) or 0.5% betaxolol (N = 10) was instilled in one randomly chosen eye and the vehicle for each drug in the other eye, and those parameters were measured as above in a double-masked manner. In the carteolol experiment, mean NB in both eyes was significantly higher at 3 hours than it was in the control experiment (P < 0.05), while intraocular pressure was significantly lower in both eyes and blood pressure and pulse rate showed little change. In the betaxolol experiment, intraocular pressure at 1.5 hours and blood pressure at 4.5 hours were significantly lower than those in the control experiment (P < 0.05), while mean NB and pulse rate showed little change. In summary, using the laser speckle method we found that topical nipradilol and carteolol increase ONH blood velocity in rabbits and humans, respectively. This finding suggests that some topical beta-blockers used clinically may influence the ONH tissue circulation in patients and that this method may be used in clinical situations to assess the effect of various drugs on ONH circulation.

Esmolol. A review of its therapeutic efficacy and pharmacokinetic characteristics

Esmolol is an ultra short-acting intravenous cardioselective beta-antagonist. It has an extremely short elimination half-life (mean: 9 minutes; range: 4 to 16 minutes) and a total body clearance [285 ml/min/kg (17.1 L/h/kg)] approaching 3 times cardiac output and 14 times hepatic blood flow. The alpha-distribution half-life is approximately 2 minutes. When esmolol is administered as a bolus followed by a continuous infusion, onset of activity occurs within 2 minutes, with 90% of steady-state beta-blockade occurring within 5 minutes. Full recovery from beta-blockade is observed 18 to 30 minutes after terminating the infusion. Esmolol blood concentrations are undetectable 20 to 30 minutes postinfusion. The elimination of esmolol is independent of renal or hepatic function as it is metabolised by red blood cell cytosol esterases to an acid metabolite and methanol. The acid metabolite, which is renally eliminated, has 1500-fold less activity than esmolol. Methanol concentrations remain within the range of normal endogenous levels. Clinically, esmolol is used for the following: (i) situations where a brief duration of adrenergic blockade is required, such as tracheal intubation and stressful surgical stimuli; and (ii) critically ill or unstable patients in whom the dosage of esmolol is easily titrated to response and adverse effects are rapidly managed by termination of the infusion. In adults, bolus doses of 100 to 200mg are effective in attenuating the adrenergic responses associated with tracheal intubation and surgical stimuli. For the control of supraventricular arrhythmias, acute postoperative hypertension and acute ischaemic heart disease, doses of < 300 micrograms/kg/min, administered by continuous intravenous infusion, are used. The principal adverse effect of esmolol is hypotension (incidence of 0 to 50%), which is frequently accompanied with diaphoresis. The incidence of hypotension appears to increase with doses exceeding 150 micrograms/kg/min and in patients with low baseline blood pressure. Hypotension infrequently requires any intervention other than decreasing the dose or discontinuing the infusion. Symptoms generally resolve within 30 minutes after discontinuing the drug. In surgical and critical care settings where clinical conditions are rapidly changing, the pharmacokinetic profile of esmolol allows the drug to provide rapid pharmacological control and minimises the potential for serious adverse effects.

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.

Randomised controlled trial of atenolol and pindolol in human pregnancy: effects on fetal haemodynamics

OBJECTIVE

To compare the effects of uteroplacental circulation of two beta adrenoceptor blockers, atenolol (cardioselective) and pindolol (non-selective with intrinsic sympathomimetic activity).

DESIGN

Controlled double blind double dummy study.

SETTING

Departments of obstetrics and gynaecology in two Swedish university hospitals.

SUBJECTS

29 women with pregnancy induced hypertension in the third trimester, 13 randomised to atenolol and 16 to pindolol.

MAIN OUTCOME MEASURES

Pulsatility index in fetal aorta, umbilical artery, and maternal arcuate artery. Volumetric blood flow in fetal aorta and umbilical vein.

RESULTS

Mean arterial blood pressure decreased by 9.0 (95% confidence interval -13.0 to -5.0) mm Hg in the atenolol group and by 7.8 (-11.4 to -4.2) mm Hg in the pindolol group. During atenolol treatment the pulsatility index increased significantly from 1.82 (SD 0.20) to 2.07 (0.32) in the fetal thoracic descending aorta, from 1.44 (0.28) to 1.79 (0.27) in the abdominal aorta, and from 0.93 (0.17) to 1.05 (0.19) in the umbilical artery; the volumetric blood flow in the umbilical vein decreased from 106 (28.8) to 84 (22.6) ml/min/kg. No such changes were seen after treatment with pindolol. Birth weight was similar in the two groups but placental weight was significantly different (529 (122) g in atenolol group v 653 (136) g in pindolol group; p = 0.03).

CONCLUSION

The hypotensive effect was similar with both drugs, but only the beta 1 blocker atenolol had significant effects on fetal haemodynamics, although within normal ranges. The implications of these findings can be only speculative, but negative fetal consequences of beta 1 adrenoceptor blockade cannot be excluded.

Differential cardiovascular effects of propranolol, atenolol, and pindolol measured by impedance cardiography

We have evaluated Sramek's method of impedance cardiography as a non-invasive way of detecting the cardiovascular effects of drugs. We made cardiovascular measurements using the method during passive tilting and exercise 2 h after the oral administration of atenolol (50 and 100 mg), propranolol (40 and 80 mg), pindolol (5 and 10 mg), and placebo in seven separate studies involving eight healthy male volunteers. Equivalent doses of the pure antagonists atenolol (beta 1) and propranolol (beta 1, beta 2) produced similar reductions in heart rate, systolic blood pressure, and cardiac index, and increases in stroke volume and total peripheral resistance, particularly during exercise. In contrast the partial agonist pindolol produced increases in heart rate and cardiac index, and reductions in peripheral resistance at rest. During passive tilting and exercise pindolol reduced heart rate, but cardiac output and total peripheral resistance were unchanged except at the highest levels of exercise. The similar cardiovascular effects of atenolol and propranolol, but differing effects of pindolol, are consistent with reports using other methods of measurement. This suggests that impedance cardiography may have a place in the non-invasive assessment of the cardiovascular effects of drugs.

Exercise performance and beta-adrenergic blockade in patients with complete heart block treated with ventricular inhibited pacing

The effect of beta-adrenergic blockade (propranolol) on exercise performance was studied in 15 patients (12 men and 3 women, mean age 70 years) with complete heart block treated with a ventricular-inhibited pacemaker (VVI). In a double-blind procedure, the patients were randomly given either 0.1 mg/kg of propranolol or saline solution i.v. before a first exercise test and vice versa before a second test. The interval between the tests was 24 hours. Nine patients were in sinus rhythm, 4 patients had atrial flutter, and 2 others had atrial fibrillation. The exercise capacity was on an average 11% lower with propranolol than with placebo (p less than 0.001). The most marked reductions (20 and 33%) were found in the two patients with atrial fibrillation. The atrial rate in patients with sinus rhythm was significantly lower with propranolol than placebo both at rest (68 vs. 83 beats/min, p less than 0.001) and at maximal work load (91 vs. 141 beats/min, p less than 0.001). The present findings show that beta blockade has negative effects on exercise capacity in patients with complete heart block treated with VVI pacemakers. This finding should be considered in the selection of drug treatment in patients with fixed rate pacing and concomitant hypertension and/or ischemic heart disease.

Propranolol and atenolol inhibit norepinephrine spillover rate into plasma in conscious spontaneously hypertensive rats

Radiotracer techniques capable of measuring norepinephrine clearance and spillover rate into plasma were used to test the hypothesis that the antihypertensive effects of propranolol and atenolol in conscious spontaneously hypertensive rats are associated with an inhibition of norepinephrine release from postganglionic sympathetic neurons. The 10%-15% fall in mean arterial pressure produced over 4 h by propranolol (1, 3.3 and 10 mg/kg, s.c.) and atenolol (1, 3.3 and 10 mg/kg, s.c.) was not dose-related, and only the largest dose of propranolol caused a significant bradycardia. Each dose of atenolol significantly lowered heart rate. The decrease in blood pressure caused by propranolol and atenolol was not related to the decrease in heart rate. Both propranolol and atenolol inhibited norepinephrine clearance by 12% to 16%. The 1 mg/kg doses of propranolol and atenolol significantly suppressed norepinephrine spillover rate by 21% and 32%, respectively, at 4 h postinjection. As the dose of propranolol was increased, the inhibition of norepinephrine spillover was reversed as plasma epinephrine concentration rose by 125%. The suppression of norepinephrine spillover rate caused by atenolol was more persistent but did diminish after the 10 mg/kg dose, when plasma epinephrine concentration was elevated by 55%. Both drugs suppressed plasma renin concentration, but the inhibition of norepinephrine spillover rate by propranolol and atenolol was not related to the fall in plasma renin concentration. By comparison, treatment with the adrenergic neuron blocking agent bretylium (5, 10, 20 and 40 mg/kg, s.c.) elicited a dose-related vasodepression with no change in heart rate or plasma renin concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Newer beta blockers and the treatment of hypertension

Beta-adrenoceptor blocking agents are established as one of the principal classes of antihypertensive agents. Despite progressive refinements over the years, they still possess some unwanted effects, which limit their considerable value. In recent years a wide range of variations upon the beta-blocker theme has been developed. The full clinical advantages of the newer agents remain to be defined.

Vasodilation, not cardiodepression, underlies the antihypertensive effect of beta-adrenoceptor antagonists

Most antihypertensive drugs act by counteracting vasoconstrictor mechanisms and lower blood pressure by lowering vascular resistance. The beta blockers, which have the unique ability to counteract cardiac sympathetic drive, seem to be a major exception to this. Moreover, their degree of cardiodepression is directly correlated with the initial sympathetic tone and also with their degree of intrinsic sympathomimetic activity (ISA). Cardiodepression initially evokes a baroreflex-mediated proportional rise in vascular resistance. As indicated by review of the literature, the antihypertensive effect of beta blockers always parallels a decline in vascular resistance. Studying beta blockers with different degrees of ISA in 50 hypertensive patients after minimizing cardiac sympathetic drive by strict bed rest showed that the initial effect of the drug is offset by a rise in vascular resistance proportional to the fall in cardiac output. After that, blood pressure always fell in parallel with vascular resistance, whatever the absolute level of cardiac output. In the long run, blood pressure and vascular resistance were always positively correlated, irrespective of the level of cardiac output. Thus, like all other antihypertensive agents, beta blockers also lower blood pressure through interference with a vasoconstrictor mechanism.

Clinical pharmacology of vasodilatory beta-blocking drugs

The clinical pharmacology of beta-adrenoceptor blockers is summarized. They have a variety of pharmacological actions on the beta-adrenoceptors. For example, propranolol is a nonselective beta-blocker with antagonist effects on both beta 1 and beta 2 receptors, atenolol is a selective beta 1-antagonist, and celiprolol is a selective beta 1-antagonist, partial beta 2-agonist. beta 1-Receptor blockade tends to reduce heart rate, cardiac output, and arterial pressure while increasing peripheral vascular resistance, whereas beta 2-receptor blockade tends to be disadvantageous in causing bronchoconstriction and peripheral vasoconstriction. Selective beta 1-antagonist, beta 2-agonist activity would, therefore, appear to be particularly beneficial in offering the advantages of beta 1 blockade plus peripheral vasodilation. The beta 1- and beta 2-receptor actions of drugs are not always clearly identifiable, as in the demonstration of celiprolol's partial beta 2-agonist activity in human beings. This is because, in vivo, cardiovascular reflexes are intact and it has not, so far, been possible to remove endogenous catecholamines. This review summarizes various studies to investigate partial agonist activity, with particular emphasis on celiprolol.

Beta-adrenergic blockade decreases norepinephrine release in humans

Beta-Adrenergic blockade with propranolol (PRP) has been reported to cause an increase in plasma norepinephrine (NE) levels in humans, which suggests that a reflex increase in sympathetic nervous system (SNS) vasoconstrictor tone compensates for the hypotensive effect of beta-adrenergic blockade. However, plasma NE levels are an indirect measure of SNS activity. We have developed a two-compartment model of NE kinetics to estimate NE release into an extravascular compartment as a more comprehensive measure of systemic SNS activity. To determine whether beta-adrenergic blockade alters extravascular NE release, we studied nine healthy subjects during sequential infusions of saline and PRP. During PRP infusion, there was an increase in plasma NE levels [1.03 +/- 0.13 to 1.27 +/- 0.21 (SE) nM; P = 0.05], but the extravascular NE release rate decreased significantly (15.5 +/- 1.6 to 9.2 +/- 1.2 nmol.min-1.m-2, P = 0.0002). The plasma NE concentration increased despite the fall in extravascular NE release rate primarily because the clearance of NE from plasma declined (1.55 +/- 0.08 to 1.18 +/- 0.07 l.min-1.m-2, P = 0.0001); the NE spillover rate into plasma did not change (1.73 +/- 0.18 to 1.75 +/- 0.23 nmol.min-1.m-2, P = 0.89). We conclude that PRP decreases extravascular NE release in humans. Suppression of SNS activity may be an additional mechanism of action of nonselective beta-adrenergic antagonists in humans.

Initial therapy for hypertension--individualizing care

Of the approximately 58 million Americans with hypertension, the majority have only mild increases in blood pressure and individually are at low risk. Large group studies, however, have demonstrated the efficacy of treating mild hypertension. Public health efforts during the past 16 years have increased the number of hypertensive patients made aware of their condition and brought into treatment. A major problem, however, is consistently maintaining patients on long-term therapy. A large number of nonpharmacologic and pharmacologic treatments have become available for the management of hypertension. These treatments must be applied individually to enhance benefit, minimize potential harm, and increase the likelihood of long-term compliance for what is often a lifelong disorder. For accomplishing this goal, a thorough understanding of important characteristics of both the individual patient and the available therapeutic modalities is needed.

Hemodynamic and beta-adrenergic receptor adaptations during long-term beta-adrenoceptor blockade. Studies with acebutolol, atenolol, pindolol, and propranolol in hypertensive patients

In an attempt to further clarify the mechanism of the maintenance of the antihypertensive effect of beta-adrenoceptor antagonists, the effects of four antagonists with different ancillary properties (acebutolol, atenolol, pindolol, and propranolol) on systemic and renal hemodynamics, body fluid volumes, hormones, and lymphocyte beta-adrenoceptor density were studied in four groups of 10 hypertensive patients. The patients were observed for 3 weeks during active treatment and for 2 weeks after withdrawal of treatment. At the end of the 3-week treatment period, the four drugs had an equal antihypertensive effect (fall in mean arterial pressure, 10-13%). Although renin activity was suppressed (60-70%) by all four drugs, changes in renin or pretreatment values of renin levels were not correlated with the fall in blood pressure. The drugs had no effect on plasma catecholamine concentrations or body fluid volumes. Despite similar antihypertensive effects among the four drugs, the changes in flow and resistance underlying the fall in blood pressure differed considerably. With pindolol, the fall in blood pressure was associated with a fall in vascular resistance (26 +/- 6%), whereas with propranolol, it was predominantly associated with a fall in cardiac output (11 +/- 7%). No significant changes in vascular resistance or cardiac output occurred with atenolol or acebutolol. The changes in renal blood flow and renal vascular resistance occurred in parallel with the changes in cardiac output and systemic vascular resistance. Plasma epinephrine concentration and pretreatment cardiac chronotropic responsiveness to isoproterenol appeared to be inversely correlated with lymphocyte beta-adrenoceptor density (Bmax) (r = -0.41 and -0.43, respectively). With pindolol, Bmax decreased maximally by 39 +/- 6%, and with propranolol, it increased by 51 +/- 17%. With both drugs, significant changes in Bmax were already present 24 hours after treatment. Furthermore, 1 week after withdrawal of treatment with pindolol, Bmax was still down-regulated, and cardiac chronotropic responsiveness was still decreased, whereas 1 week after withdrawal of propranolol, Bmax was still up-regulated, and cardiac chronotropic responsiveness was still increased. No changes in Bmax occurred with the beta 1-selective antagonists acebutolol and atenolol. Thus, despite an equal antihypertensive effect, the four beta-adrenoceptor antagonists appear to have dissimilar effects on cardiac output, renal blood flow, and lymphocyte beta-adrenoceptors. Changes in cardiac output, the circulating blood volume, or angiotensin-mediated vasoconstriction are factors unlikely to be crucial for the antihypertensive effect of beta-adrenoceptor antagonists. Therefore, interference with vasoconstrictor nerve activity through blockade of either central or peripheral prejunctional beta-adrenoceptors could be an alternative explanation of their blood pressure-lowering potential.

Combination therapy with calcium-entry blockers and beta-adrenoceptor antagonists in hypertension

The use of more than one drug to control blood pressure may be necessary in up to 50% of hypertensive patients seen in clinical practice. A rational basis for combination therapy includes 1) the use of drugs that act on different physiological systems involved in blood-pressure control and 2) using a second drug to counteract reflex responses, which may limit the effectiveness of the first, and, 3) as is less commonly practiced, the use of low doses of two drugs that act on the same or different physiological systems to avoid the side effects encountered with higher doses of single agents. The hemodynamic effects of calcium-entry blocking drugs and beta-adrenoceptor blockers are complementary and synergism might be anticipated, particularly with the dihydropyridines and beta-blockers, since the latter prevent the short-term reflex increase in sympathetic activity occurring as a consequence of vasodilation. Although there are many studies advocating the benefits of such combinations, caution is required with combinations of beta-blockers and verapamil or diltiazem because of potential cardiac depressant effects resulting from the more complex effects of these calcium-channel blockers on cardiac myo-cytes and conducting tissue. Such problems would be more likely to be encountered in patients with long-standing hypertension and in whom poor left ventricular function and coro-nary artery disease may be present.

Exercise haemodynamic effects of beta-blockade and intrinsic sympathomimetic activity

Beta-adrenergic blockade with intrinsic sympathomimetic activity (ISA) causes less depression of resting and submaximal heart rate (HR) than non-ISA beta-blockers. The effects of these drugs on exercise haemodynamics have not been well studied. We evaluated effects of pindolol, propranolol and placebo during rest and steady-state exercise on cardiac output, oxygen consumption, calf blood flow, HR and blood pressure in 18 healthy subjects. Pindolol 5 mg and propranolol 80 mg given twice daily, reduced maximal exercise HR by 50 and 52 beats.min-1 respectively, confirming similarity of beta 1-blockade. Resting cardiac output was unchanged in all three groups after one week of therapy. Cardiac output, measured during steady-state exercise decreased in the propranolol group (18.3 vs 15.6 l.min-1) with no significant changes in pindolol (15.7 vs 16.01.min-1) or placebo (18.6 vs 17.3 l.min-1). The rise in cardiac output, from rest to exercise, was similarly attenuated by propranolol but not by pindolol or placebo. Exercise stroke volume increased 12% on pindolol (123-140 cc) and decreased 7% on propranolol (143-133 cc). Neither drug had a detrimental effect on exercise calf blood flow compared to placebo. Thus, unlike propranolol, pindolol with ISA, maintains a normal cardiac output during submaximal exercise.

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.

Hemodynamic and hormonal adaptations to beta-adrenoceptor blockade. A 24-hour study of acebutolol, atenolol, pindolol, and propranolol in hypertensive patients

Comparison of the hemodynamic and hormonal effects of beta-adrenoceptor antagonists with different ancillary properties may help to clarify the antihypertensive mechanism of these drugs. Under strict basal conditions, the effects of acebutolol (400 mg b.i.d.), atenolol (100 mg b.i.d.), pindolol (10 mg b.i.d.), and propranolol (80 mg t.i.d.), were studied for the first 24 hours in 40 hypertensive patients. With pindolol, mean arterial pressure was reduced (p less than 0.05) 1 hour after administration, whereas the cardiac index and the systemic vascular resistance index did not change. With the other three drugs, the fall in mean arterial pressure was delayed 2-3 hours. With these drugs, the fall in mean arterial pressure was preceded by a rise in the resistance index, which compensated for the initial fall in cardiac index. With each drug, the decrements in mean arterial pressure were associated with parallel decrements in the resistance index, and percent changes in mean arterial pressure and the resistance index were always significantly (p less than 0.001) correlated. At the end of the 24-hour period, the four drugs shared an equal antihypertensive effect, which varied 14-17%. This was associated with a return of the cardiac index toward control values by acebutolol, atenolol, and propranolol treatment and a moderately increased cardiac index above pretreatment values (13%, p less than 0.01) with pindolol. The secondary rise in the cardiac index was inversely correlated (p less than 0.001) with the fall in mean arterial pressure with all four drugs. Plasma renin was maximally suppressed 2 hours after treatment, thus before any change in mean arterial pressure had occurred with acebutolol, atenolol, and propranolol. Pretreatment values of active renin and the reduction of mean arterial pressure 24 hours after administration were not correlated in any of the four groups. Despite the "vasodilator" action of the four drugs, plasma norepinephrine did not rise. Our data show that the main hemodynamic change that occurs at the time blood pressure falls after beta-adrenoceptor antagonism is vasodilation. Neither autoregulation of blood flow nor renin suppression can explain this vasodilator action. The absence of an increase in norepinephrine, despite vasodilation, suggests that beta-adrenoceptor antagonism interferes with sympathetic vasoconstrictor nerve activity. This effect may explain the vasodilator and antihypertensive potential of beta-adrenoceptor antagonists.

Xamoterol. A preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use

Xamoterol is a partial agonist at the beta 1-adrenoceptor. Haemodynamic studies indicate that xamoterol moderately increases myocardial contractility, improves diastolic relaxation and lowers left ventricular filling pressure at rest and during moderate exercise. At higher levels of sympathetic activity (e.g. strenuous exercise) it produces negative chronotropic responses whilst the reduced filling pressure is maintained. Studies in patients with mild to moderate chronic heart failure demonstrate an advantage for xamoterol 200mg twice daily over placebo and digoxin with respect to improvement in exercise capacity and symptoms. In limited trials to date the initial response seems to be maintained during periods of up to 12 months. Preliminary small studies suggest that xamoterol is useful in the treatment of some patients with angina pectoris, sinoatrial disease or postural hypotension, although further studies are needed to confirm its clinical role in such patients. Xamoterol appears to be generally well tolerated, but deleterious effects in a small number of patients with asthma, or severe heart failure due to dilated cardiomyopathy indicate the need for cautious use of xamoterol in patients with these diseases. Thus, xamoterol is a promising addition to the drugs available to the physician for treating patients with mild to moderate heart failure although further controlled studies are required to clearly establish its precise role.

Progress in antihypertensive therapy with a multiple-action drug

The beta-blockers in clinical use have been classified into 2 major divisions, nonselective or selective agents, and those with or without intrinsic sympathomimetic activity (ISA). These properties confer differing pharmacological properties with some relevance to the treatment of hypertension. A beta-blocker with significant beta 2-ISA can be regarded as a multiple-action drug. A third division of beta-blockers is a newer development; these agents, besides blocking the beta-receptor, possess important peripheral vasodilator activity. Labetalol was the first drug of this group and prizidolol followed, but has been withdrawn because of toxicity. Several other agents now under evaluation include bucindolol and medroxolol, and carvedilol and dilevalol (1 of the isomers of labetalol), which have been the most widely studied in hypertension. Combined action results in important haemodynamic differences compared with pure beta-blockade. Notably, peripheral resistance is reduced, and there is less reduction in, or no effect on, cardiac output. The 3 following mechanisms have been described as responsible for peripheral vasodilatation: alpha-receptor blockade, beta 2-agonism, and a dilator action independent of either the alpha- or beta-receptors. Evidence for these various mechanisms is more readily obtainable from animal experiments, but some confirmatory evidence has been obtained in man. Inhibition of alpha-stimulation has been found with labetalol and to a small degree with medroxalol and carvedilol. beta 2-Mediated vasodilatation has been shown by dilevalol and medroxolol, and evidence of vasodilatation independent of alpha- or beta-receptors has been obtained with carvedilol. More evidence is required to confirm the exact contribution of each of these mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Haemodynamic effects of new beta-blockers with vasodilatory properties in essential hypertension

Six weeks of treatment with carvedilol, N-696, celiprolol, dilevalol, acebutolol, urapidil, doxazosin and altiopril reduced blood pressure with various changes in heart rate. Cardiac index decreased and total peripheral resistance index (TPRI) stayed at the pretreatment levels in the carvedilol, N-696 and acebutolol groups, whereas TPRI tended to decrease in the celiprolol (p less than 0.05), dilevalol (p less than 0.05), urapidil, doxazosin (p less than 0.05) and altiopril groups; cardiac index was unchanged in these groups. As carvedilol and N-696 have no beta 1-selectivity and no intrinsic sympathomimetic activity (ISA), their direct vasodilating property (and the possible alpha-blocking activity of carvedilol) may precipitate in minimising an increase in TPRI induced by vascular beta 2-blockade and suppressed cardiac pump function. Celiprolol and dilevalol, with beta 2-selective ISA, reduced cardiac index slightly and insignificantly, and decreased TPRI. These results indicate that ISA on vascular beta 2-receptors may induce vasodilatation and ISA on cardiac beta 2-receptors may counteract cardiac beta 2-blockade. Differences in haemodynamic responses between these drugs with ISA and vasodilators such as alpha-blocking agents (urapidil and doxazosin) and an ACE inhibitor, altiopril, may be attributable to manifestation of cardiac beta-blockade as observed in the drugs with ISA.

Drug treatment of hypertension

There are several first choices for the treatment of mild and moderate hypertension. The selection of a drug may be influenced by concomitant pathology, with positive indications for particular drugs, e.g. coexistent angina, indicating use of a beta-receptor blocking drug or calcium antagonist; fluid retention indicating a diuretic; or contraindication e.g. asthma, and beta-adrenoceptor blocking drugs. beta-Adrenoceptor blocking drugs have the advantage of a long history and of possibly being cardioprotective following myocardial infarction, but they have not yet been established as primary preventive agents in hypertensive patients. The alpha-receptor blocking drugs have the advantage of favourably affecting lipid profile and blood pressure. Therefore, there may be advantages in the use of combined alpha- and beta-blockade. The diuretics, which have the advantage of being inexpensive, are widely used but long term metabolic effects, particularly hypokalaemia, cause concern. This is correctable by co-administration of a potassium sparing diuretic and often preventable by using low doses of the diuretic. Diet may be important as hypokalaemia appears to be less of a problem where potassium intake is high. Experience with calcium antagonists is widening but the use of converting enzyme inhibitors is more limited, and some physicians are less ready to use them as first choice in mild hypertension at present. Drugs like methyldopa, clonidine, the adrenergic neurone inhibitory drugs are now used more as reserve agents. More severe cases of hypertension may require drugs from 2 of the 3 major groups: beta-blocking drugs, vasodilators and diuretics. In some cases, drugs from each of these 3 groups will be required.

Effect of acute administration of propranolol and atenolol on baroreflex function in normal man

The acute administration of the beta-adrenoceptor antagonists propranolol (80 mg) and atenolol (50 mg) on baroreflex function were investigated in healthy volunteers. Two h after administration both propranolol and atenolol significantly prolonged the supine R-R interval (1126, 1128 ms respectively) compared to placebo (1012 ms); systolic arterial pressure also fell (102.9, 102.0 mm Hg respectively) compared to placebo (112.6 mm Hg). Baroreflex function, assessed using glyceryl trinitrate to deactivate the baroreceptors was unchanged by these drugs compared to placebo. Baroreflex sensitivity (slope of the linear regression line relating R-R interval to systolic blood pressure) using phenylephrine to activate the baroreceptors, was also unchanged (17.2, 17.9 ms/mm Hg respectively) compared to placebo (19.9 ms/mm Hg). However both regression lines were shifted (p less than 0.05) to the left compared to placebo.

The total vascular burden, peripheral and coronary: vasodilator effects of nifedipine

While the total ischemic burden on the left ventricle represents the combined effects of both symptomatic and asymptomatic myocardial ischemia, the total vascular burden has many components including an increased systemic peripheral vascular resistance, an increased pulmonary vascular resistance, and an increased coronary vascular resistance. These factors may all influence ventricular function. Hypertension contributes significantly to the vascular burden, especially when combined with left ventricular hypertrophy, which predisposes to ischemia by multiple mechanisms. In patients with hypertension and cardiomegaly, sublingual nifedipine has been shown to increase left ventricular (LV) ejection fraction and the average diastolic filling rate. In the presence of acute myocardial infarction, nifedipine moves the LV function curve onto a better Frank-Starling relationship as pulmonary wedge pressure falls or stays the same and cardiac output rises. However, because of the delicate balance between myocardial perfusion and the benefits of afterload reduction, including improved remodelling, nifedipine should be given only to selected patients. In congestive heart failure, low-dose nifedipine reduces the afterload and has been shown to have beneficial effects in the majority of patients. Two specific adverse outcomes in only two patients have been reported, one with initial hypotension and one given high-dose nifedipine. Combination nifedipine-beta blocker therapy has been shown to be favorable in the treatment of all varieties of angina, hypertension, and hypertrophic cardiomyopathy. Therefore, when administered appropriately, nifedipine reduces the total vascular burden on the heart in a variety of cardiovascular diseases, with consequent improvement in LV function and a diminished threat of potential myocardial ischemia.

Celiprolol. A preliminary review of its pharmacodynamic and pharmacokinetic properties and its therapeutic use in hypertension and angina pectoris

Celiprolol is a new 'cardioselective' beta-adrenoceptor blocking drug with intrinsic sympathomimetic (partial agonist) activity and a weak vasodilating effect. Celiprolol appears not to cause bronchoconstriction or inhibit the effect of bronchodilating drugs in asthmatic patients and there is some evidence that it may have mild bronchodilating activity in such patients. Some studies suggest that celiprolol, because of vasodilation, may be less likely to reduce blood flow to the peripheries than other beta-adrenoceptor blocking drugs and hence cause fewer peripheral vascular side effects. Significant inhibition of exercise tachycardia occurs 24 hours after a single oral dose of celiprolol. In preliminary therapeutic trials celiprolol 200 to 600mg once daily was similar in efficacy to propranolol 40mg to 80mg twice daily or atenolol 100mg once daily in patients with mild to moderate hypertension or angina pectoris. If the apparent pharmacodynamic advantages of celiprolol are confirmed in well designed therapeutic trials then celiprolol should represent a definite advance in beta-adrenoceptor blocking therapy.

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.

Pharmacologic aspects of intrinsic sympathomimetic activity in beta-blocking drugs

The possession of intrinsic sympathomimetic activity (ISA) by a beta-adrenoceptor blocking drug results in a number of different pharmacologic properties. Most profound are the central hemodynamic effects. A drug with a significant degree of ISA results in less of a decrease in heart rate at rest and cardiac output, and, at least partly because of this, less of a decrease in peripheral blood flow. If prevailing sympathetic tone is low enough (e.g., during sleep) and the degree of ISA is sufficient, an increase in heart rate may be seen from an ISA-possessing drug. If the drug possesses beta 2 ISA, then a peripheral vasodilation action from stimulation of beta 2 vasodilator receptors may also be relevant. If high levels of exercise and full dosages of the drugs are used, a beta-blocking drug with ISA produces less of a decrease in heart rate. In asthmatic subjects, the modest beta-stimulant action on bronchial smooth muscle is not important, as these patients are potentially sensitive to any receptor blockade. Isoprenaline responses are inhibited to a similar degree compared with inhibition of exercise tachycardia, by nonselective drugs with and without ISA, whereas beta 1 selective agents produce much less inhibition of isoprenaline-induced tachycardia. A drug with ISA "down regulates" beta receptors; thus, when the drug is withdrawn there is no post-beta-blocking drug hypersensitivity in contrast to agents without ISA. There is evidence that ISA results in less of a disturbance in certain metabolic processes, particularly lipid metabolism and the metabolism of liver-metabolized drugs.

Fetal and uteroplacental haemodynamics during short-term atenolol treatment of hypertension in pregnancy

Fetal circulation was studied by means of combined real-time and pulsed Doppler ultrasound in 14 women with pregnancy-associated hypertension before and during the first and third days of treatment with the beta 1-selective blocker, atenolol; in seven of the women the maternal uterine arcuate blood velocity waveform was also studied. Blood flow characteristics were normal both in the fetus and in the maternal arcuate artery, compared with those in uncomplicated pregnancies of corresponding gestational ages. Volume blood flow remained unchanged in the fetal descending aorta, and in the umbilical vein during atenolol treatment, whereas the pulsatility index increased in the fetal descending aorta and in the arcuate artery. This suggests that the peripheral vascular resistance, both on the maternal and fetal side of the placenta, increased during short-term antihypertensive treatment with atenolol.

Ophthalmic beta-blockers since timolol

In the twenty years since beta-blockers were proposed for treatment of glaucoma, use of topical timolol has increased to account for 70% of all glaucoma medications used. The objective of this article is to review the "newer" beta-blockers, and to address the generalization that "all ophthalmic beta-blockers are the same." The review concentrates on agents that have been studied as topical treatments for patients with elevated intraocular pressure. Sections on pharmacology and design of clinical trials are included to aid the ophthalmologist in evaluating the new drugs and published clinical reports. The major questions to consider in evaluating the therapeutic potential of a new beta-blocker for the treatment of glaucoma involve efficacy and safety: Is the drug as effective as timolol? Does it have a duration of action at least as long as timolol? Does it have ocular toxicity? Is it comfortable? What are its systemic effects?

Is beta 1-antagonism essential for the antihypertensive action of beta-blockers?

Both nonselective beta-blockers and beta 1-selective blockers are effective antihypertensive agents. beta 1-Blockade generally is considered to be responsible for their antihypertensive action, whereas beta 2-blockade is regarded as undesirable. These common assumptions notwithstanding, the mechanism by which beta-blockers lower blood pressure remains unknown. To examine the possibility that beta 2-blockade may contribute to the antihypertensive action of beta-blocker therapy, we studied the cardiovascular effects of compound ICI 118551, a beta 2-selective blocker. First, we showed that 50 mg t.i.d. orally is a beta 2-selective dose. In contrast to propranolol, 80 mg t.i.d., or atenolol, 100 mg once a day, 50 mg of ICI 118551 t.i.d. failed to block beta 1-mediated inotropic stimulation and stimulation of renin by isoproterenol. We then performed a double-blind, placebo-controlled trial in patients with mild essential hypertension to compare this compound with propranolol, 80 mg t.i.d., and showed that ICI 118551 significantly decreased systolic and diastolic blood pressure. This antihypertensive effect was demonstrated by direct as well as by indirect blood pressure measurements. Thus, contrary to prevailing thought, beta 2-blockade has an antihypertensive effect independent of, and distinct from, beta 1-blockade.

Interaction between two calcium antagonists and two beta blockers in conscious rabbits: hemodynamic consequences of differing cardiodepressant properties

The interaction between beta-adrenoreceptor blockers and calcium antagonists may occasionally be dangerous. The effects of the new calcium antagonist PN 200-110 (isradipine) were compared with those of verapamil in 3 groups of conscious rabbits pretreated with either pindolol 0.3 mg/kg, propranolol 1 mg/kg intravenously or placebo. Each animal received PN 200-110 (0.01, 0.03 and 0.1 mg/kg) and 2 or more days later verapamil (0.1, 0.3 and 1 mg/kg). The calcium antagonists were given to lower mean blood pressure to the same extent as in the placebo group. This blood pressure effect remained unchanged after pretreatment with pindolol or propranolol. Both PIN 200-110 and verapamil increased heart rate to the same extent as in the placebo group. Both beta blockers blunted the effect of PN 200-110 on heart rate but converted the verapamil-induced tachycardia to bradycardia. Propranolol blunted the PN 200-110-induced increase in cardiac output and total peripheral conductance, whereas the high verapamil dose decreased cardiac output and caused peripheral vasoconstriction in propranolol-pretreated animals. Thus, both agents lowered blood pressure by peripheral vasodilatation in the placebo group, after beta blockade; however, the mechanism of the verapamil-induced blood pressure decrease changed from pure vasodilation to a decrease in cardiac output, i.e., cardiac depression. Verapamil but not PN 200-110 prolonged the PQ interval, especially in animals who had received beta blockade. Most differences in the interaction were attributable to differences between the 2 calcium antagonists; the differences between the beta blockers were small and in favor of pindolol.

Comparison of the onset of the antihypertensive action of pindolol and propranolol. A 24 h haemodynamic study

1. Haemodynamic changes during the onset of the antihypertensive action of pindolol, 10 mg twice daily, and propranolol, 80 mg three times daily, were studied for 24 h in two groups of 10 patients with uncomplicated essential hypertension. 2. Baseline haemodynamics were not different between the two groups. 3. Pindolol, with considerable intrinsic sympathomimetic activity (ISA) exerted its maximal antihypertensive efficacy within 3-4 after dosing (-15 +/- 3%, mean +/- s.e. mean, P less than 0.001). This effect was maintained for 24 h. 4. After propranolol, which is devoid of ISA, arterial pressure fell more gradually, but after 24 h the two drugs shared an equal antihypertensive effect. 5. Cardiac output rose after pindolol by 16 +/- 5% (P less than 0.01). It decreased transiently by 16 +/- 6% (P less than 0.01) 1-4 h after propranolol. At that time vascular resistance had risen by 18 +/- 5% (P less than 0.001). 6. The onset of the antihypertensive action of the two drugs was associated with reductions in vascular resistance. Since reflex vasoconstriction did not occur after pindolol, vascular resistance was always lower on this drug than on propranolol (-29 +/- 4%, P less than 0.001 vs -15 +/- 5%, P less than 0.01). 7. Cardiac filling pressures, pulmonary artery pressure and pulmonary vascular resistance did not change after pindolol but they rose after propranolol. 8. During the onset of the vasodilator and antihypertensive effects of the two beta-adrenoceptor blockers heart rate, stroke volume and cardiac output rose, despite cardiac beta-adrenoceptor blockade, suggesting a reduction of parasympathetic tone and an increase in venous return.(ABSTRACT TRUNCATED AT 250 WORDS)

Large arteries in hypertension: heterogeneous haemodynamic response to beta-adrenoceptor antagonists with and without intrinsic sympathomimetic activity

1. Hypertension is associated with a distension of the large arteries and consequently a marked reduction in arterial compliance, which does not result merely from the mechanical effects of elevated arterial pressure but also from early functional and/or structural changes in the arterial walls. This suggests that one of the aims of antihypertensive therapy should be to reverse these arterial abnormalities in the hope of protecting the patient from the atherosclerotic complications of hypertension. 2. Studies have been carried out to compare the effects of equieffective antihypertensive doses of pindolol and propranolol on the arterial circulation in patients suffering from essential hypertension. After 3 months therapy pindolol produced a dilatation of the brachial artery with an increase in arterial compliance and blood flow. In contrast, propranolol, despite comparable antihypertensive effects, did not influence brachial artery circulation. 3. These different effects on the arterial circulation presumably reflect the differing pharmacological properties of the two beta-adrenoceptor antagonists and suggest that the intrinsic sympathomimetic activity of pindolol may be responsible for the qualitative differences in the arterial responses to the two drugs. 4. The results reviewed here reveal that even when two drugs of the same class are used to treat patients with essential hypertension the effects of these agents on arterial haemodynamics can vary greatly and are unrelated to the degree of blood pressure lowering. Thus, pindolol, in contrast to propranolol, not only lowers blood pressure but also reverses some of the changes in arterial haemodynamics which are characteristic of hypertensive disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac effects of beta-adrenoceptor blockade with intrinsic sympathomimetic activity during submaximal exercise

1. beta-adrenoceptor blocking agents with intrinsic sympathomimetic activity (ISA) are characterized by lesser depression of cardiac performance during low levels of sympathetic stimulation than beta-adrenoceptor blocking agents lacking ISA. Studies of the effects of ISA on cardiac output and on the determinants of myocardial oxygen demand during submaximal exercise are described and distinct differences between beta-adrenoceptor antagonists with and without ISA emerge. 2. At doses which produce similar effects on maximal exercise heart rate, and resting and exercise systolic blood pressure, pindolol, a beta-adrenoceptor blocking agent with substantial ISA, allows a higher submaximal exercise cardiac output and submaximal heart rate X systolic blood pressure product than does propranolol, a beta-adrenoceptor antagonist without ISA. 3. These findings may have clinical relevance in specific groups of patients such as those with arterial hypertension, where the preservation of cardiac function may allow for a more physiologic exercise response. Implications in patients with coronary artery disease and chronic heart failure await further study.

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.