Systemic and renal vasodilation after beta-adrenoceptor blockade with pindolol: a hemodynamic study on the onset and maintenance of its antihypertensive effect

Assessment of arterial ventricular coupling changes in patients under therapy with various antihypertensive agents by a non-invasive echocardiographic method

BACKGROUND

The integration between arterial and ventricular function has been studied by mostly invasive techniques. We considered assessing the influence of various antihypertensive medications on arterial-ventricular coupling (AVC) with the use of a non-invasive echocardiographic method.

METHODS

A total of 9037 patients, who had been under treatment for essential arterial hypertension were studied echocardiographically at baseline prior to therapy and after 6 months of antihypertensive monotherapy (diuretics, beta-blockers without intrinsic sympathomimetic activity (ISA), beta-blockers with ISA, a-blockers, angiotensin converting enzyme inhibitors (ACEI), angiotensin II receptor blockers (AIIRA), non-dihydropyridine calcium antagonists, and dihydropyridine calcium antagonists). The AVC was calculated by echocardiographic measurements based on the equation: AVC=ESV/SV (ESV, end systolic volume; SV, stroke volume).

RESULTS

ACEI, AIIRA, and dihydropyridine calcium antagonists decreased (P<0.0001 for all) while diuretics, alpha-blockers, both beta-blocker groups, and non-dihydropyridines increased significantly the AVC values compared to baseline measurements (P<0.0001 for all, except P=0.02 for alpha-blockers). Changes in AVC were the most highly correlated with changes in EF (r=-0.979, P<0.0001).

CONCLUSION

Various antihypertensive drugs have a differential effect on AVC with ACEI, AIIRA, and dihydropyridine calcium antagonists having the most favorable effect on this index. AVC provides a meaningful index of cardiovascular performance in hypertension and offers the possibility of wide employment and serial follow-up in large numbers of patients because of its completely non-invasive nature.

Renal and limb vasodilatation during acute beta-adrenoceptor blockade with indenolol

Indenolol is a noncardioselective beta-adrenoceptor blocking drug with partial agonist activity. The mechanism of its acute antihypertensive activity has been evaluated in a double-blind, inpatient, crossover, randomized study versus placebo in 12 patients (eight men, four women, mean age 53 +/- 13 yr) with I and II WHO grade essential hypertension. Patients discontinued all antihypertensive and diuretic drugs at least 4 weeks before entry into the study. The effects of indenolol (120 mg) and placebo (2 weeks apart) were measured, in the same patient, 2 hours after a single oral administration. Variations of cardiac function were assessed by radionuclide angiocardiography, renal blood flow by sequential scintigraphy, and leg blood flow by strain-gauge plethysmography. Compared with placebo, indenolol reduced systolic blood pressure by 27.9 mm Hg and diastolic blood pressure by 17.1 mm Hg. Heart rate was also significantly decreased. The hemodynamic profile of indenolol activity was characterized by a decrease of cardiac index, without significant changes in systemic vascular resistance. Both renal and leg blood flow were increased by indenolol, and vascular resistance in these districts was considerably reduced. The percent reduction of renal vascular resistance was correlated significantly with the percent reduction of mean blood pressure. In conclusion, acute administration of indenolol exerts a considerable antihypertensive activity associated with a marked vasodilation in vascular districts involved in the progression of hypertensive disease such as the renal and muscular vasculature.

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

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

Sleep patterns and blood pressure variability in patients with pure autonomic failure

Sleep patterns and 24-h blood pressure variability were studied in four female patients (age range: 56-82 years) with pure autonomic failure. All patients had severe symptomatic postural hypotension, without neurological deficits. In these patients the following patterns were observed: (i) a reversed diurnal blood pressure pattern, with the highest values observed at sleep onset; (ii) a prolonged sleep latency and increased amount of stage 3 sleep; (iii) difficulty with getting up after awakening in the morning, due to severe postural hypotension; (iv) an absence of prominent respiratory abnormalities during sleep; and (v) a dissociation between respiratory and haemodynamic findings. It is concluded that isolated deficiency of presumed postganglionic autonomic function influences sleep architecture, probably through absence of buffering of diurnal haemodynamic alterations, such as by postural hypotension and its consequences for body fluid volume regulation. This may be of relevance when sleep patterns are studied in other types of autonomic failure with postural hypotension involving central or preganglionic lesions, as in patients with the Shy-Drager syndrome or multiple system atrophy.

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.

Support for adrenaline-hypertension hypothesis: 18 hour pressor effect after 6 hours adrenaline infusion

In a double blind, crossover study 6 h infusions of adrenaline (15 ng/kg/min; 1 ng = 5.458 pmol), noradrenaline (30 ng/kg/min; 1 ng = 5.911 pmol), and a 5% dextrose solution (5.4 ml/h), were given to ten healthy volunteers in random order 2 weeks apart. By means of intra-arterial ambulatory monitoring the haemodynamic effects were followed for 18 h after the infusions were stopped. Adrenaline, but not noradrenaline, caused a delayed and protracted pressor effect. Over the total postinfusion period systolic and diastolic arterial pressure were 6 (SEM 2)% and 7 (2)%, respectively, higher than after dextrose infusion (ANOVA, p less than 0.001). Thus, "stress" levels of adrenaline (230 pg/ml) for 6 h cause a delayed and protracted pressor effect. These findings are strong support for the adrenaline-hypertension hypothesis in man.

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.