Comparison of the effects on renin release of beta adrenergic antagonists with differing properties

Non-obvious correlations to disease management unraveled by Bayesian artificial intelligence analyses of CMS data

OBJECTIVE

Given the availability of extensive digitized healthcare data from medical records, claims and prescription information, it is now possible to use hypothesis-free, data-driven approaches to mine medical databases for novel insight. The goal of this analysis was to demonstrate the use of artificial intelligence based methods such as Bayesian networks to open up opportunities for creation of new knowledge in management of chronic conditions.

MATERIALS AND METHODS

Hospital level Medicare claims data containing discharge numbers for most common diagnoses were analyzed in a hypothesis-free manner using Bayesian networks learning methodology.

RESULTS

While many interactions identified between discharge rates of diagnoses using this data set are supported by current medical knowledge, a novel interaction linking asthma and renal failure was discovered. This interaction is non-obvious and had not been looked at by the research and clinical communities in epidemiological or clinical data. A plausible pharmacological explanation of this link is proposed together with a verification of the risk significance by conventional statistical analysis.

CONCLUSION

Potential clinical and molecular pathways defining the relationship between commonly used asthma medications and renal disease are discussed. The study underscores the need for further epidemiological research to validate this novel hypothesis. Validation will lead to advancement in clinical treatment of asthma & bronchitis, thereby, improving patient outcomes and leading to long term cost savings. In summary, this study demonstrates that application of advanced artificial intelligence methods in healthcare has the potential to enhance the quality of care by discovering non-obvious, clinically relevant relationships and enabling timely care intervention.

Mode of action of beta-adrenoceptor blocking agents in hypertension. A comparison between metoprolol and pindolol with special reference to peripheral vascular effects

beta-Adrenoceptor blocking drugs are generally recognized as being effective in the treatment of hypertension. The mechanisms whereby these drugs reduce blood pressure are, however, not fully understood. In a double-blind, randomized study either metoprolol, 100--300 mg/day, or pindolol, 5--15 mg/day, was given for 6 months and the effects on blood pressure, heart rate and vascular resistance in the calf and forearm were investigated. Measurements were made at rest, during and after physical exercise, and during postischaemic hyperaemia. Both drugs reduced blood pressure to the same extent both at rest and during and after exercise. Metoprolol reduced heart rate to a greater extent than pindolol at rest and after exercise, whereas no difference was seen during physical exercise. Pindolol reduced the vascular resistance in the calf at rest by 14% (p less than 0.05), whereas metoprolol tended to increase vascular resistance, the difference in effect being highly significant (p less than 0.005). During and after leg exercise, there was no difference in forearm vascular resistance between the two drugs. It may be concluded that pindolol reduced resting blood pressure partly through peripheral vasodilatation. This was probably an effect of beta 2-adrenoceptor stimulation linked to the pronounced intrinsic sympathomimetic activity (ISA) of pindolol. Metoprolol on the other hand, acted mainly through cardiac mechanisms, as suggested by its pronounced reduction of heart rate.

Choosing the right ACE inhibitor. A guide to selection

To find out if there are one or more criteria to guide selection among the ACE inhibitors for the treatment of arterial hypertension, we have reviewed the principal pharmacokinetic and pharmacodynamic aspects of the more frequently used agents of this class of antihypertensive drugs. Among the pharmacokinetic aspects that we have considered, terminal half-life, as related to the duration of the antihypertensive effect, and the route of elimination may have an impact in the clinical selection among the various ACE inhibitors. On the other hand, all the other characteristics have no pragmatic clinical relevance or may be corrected by dosage adjustment. Among the pharmacodynamic aspects, the antihypertensive efficacy of the different ACE inhibitors seems to be very similar, and some of the differences found in different studies are probably due to the population investigated and to the protocol of the study (time of blood pressure measurements, diet, drug dosage etc.). However, some differences can be found among the various ACE inhibitors when the antihypertensive efficacy is evaluated also as trough to peak ratio of blood pressure reduction. Indeed, in respect of the administration schedule of each ACE inhibitor not all the agents of this class have a trough to peak ratio above 50 to 60%, as suggested by the Food and Drug Administration of the US. According to this criterion, especially when blood pressure is measured with 24-hour noninvasive ambulatory blood pressure monitoring, some drugs such as lisinopril, enalapril and trandolapril should be preferred for their higher trough to peak ratios. Left ventricular hypertrophy is significantly reduced by antihypertensive agents, the ACE inhibitors being the most effective. Indeed, the reduction of left ventricle mass for each 1 mm Hg reduction in mean blood pressure is greater for ACE inhibitors than for other classes of antihypertensive agents. However, this effect seems more class related than characteristic of one or more among the various ACE inhibitors. Insulin resistance is elevated in hypertensive patients and it has been thought responsible for or associated with other metabolic abnormalities. ACE inhibitors seem to correct the insulin resistance of hypertensive patients, but this effect also appears to be class related more than limited to one ACE inhibitor or another. Our knowledge of this field is still limited and more studies are necessary, especially to understand the prognostic impact of insulin resistance and/or insulin resistance improvement.(ABSTRACT TRUNCATED AT 400 WORDS)

Assessment of renin dependency of hypertension with a dipeptide renin inhibitor

To evaluate the participation of the renin-angiotensin system in sustaining hypertension, we administered the specific dipeptide renin inhibitor enalkiren (A-64662) to 18 patients with essential hypertension. Ascending intravenous bolus doses (0.03, 0.1, 0.3, and 1.0 mg/kg) of the inhibitor were each given at 45-minute intervals to patients maintained on an ad libitum sodium diet who were studied while in bed in the semirecumbent posture. Enalkiren produced marked decreases in plasma renin activity (PRA) that were still evident 8 hours after completion of dosing. Systolic and diastolic blood pressures were decreased in a dose-dependent fashion without an effect on heart rate. Repetition of this procedure after patients were subjected to sodium depletion by 1 week of thiazide treatment produced amplified decreases in blood pressure. Despite the short plasma half-life of the inhibitor, these blood pressure-lowering effects were sustained for 4-8 hours when compared with parallel placebo administration in the same patients. Both the baseline PRA and the inhibitor-induced changes in PRA correlated significantly with blood pressure changes during the unstimulated and the sodium-depleted studies. However, effects of the inhibitor on diastolic blood pressure in the latter study correlated most closely with actual increases in renin produced by diuretic pretreatment. Thus, this specific renin inhibitor has demonstrated the dependency of blood pressure on the renin-angiotensin system even during basal conditions in hypertensive patients. Moreover, renin response to sodium depletion appears to be an attribute that additionally characterizes individual hypertensive patients.

Prevention of arterial disease in experimental renal hypertension

1. This study examined the effect of various antihypertensive agents on the development of polyarteritis nodosa lesions along the mesenteric artery system over a 10 week period after renal artery clipping in uninephrectomized rats (lKlC). 2. Of the agents, only hydralazine, enalapril and diltiazem significantly inhibited systolic blood pressure (SBP) rise over the 10 week period (P less than 0.001). 3. All agents except hydralazine reduced the severity of arteritic lesions compared with lKlC rats, but only with enalapril (P less than 0.001), nifedipine (P less than 0.001), diltiazem (P less than 0.005), propranolol (P less than 0.001) and reserpine (P less than 0.05) was this reduction statistically significant. 4. There was a positive correlation between the degree of arteritic change and SBP, but the correlation coefficient was neither high (r = 0.68) nor highly significant (P = 0.03, d.f. = 9). On examining the data, this was due on the one hand to nifedipine, propranolol and reserpine reducing the severity of lesions without significantly inhibiting SBP, and on the other to hydralazine reducing SBP without significantly affecting the extent of arteritic change. 5. These findings suggest that factors other than mere SBP alone are involved in the pathogenesis of these arteritic lesions.

Beta blockers in hypertension

Beta-adrenoceptor antagonists are effective in the management of patients with mild-to-moderate hypertension. Noncardioselective agents, cardioselective agents and beta blockers with intrinsic sympathomimetic activity (ISA) are equally effective, provided they are used in equipotent doses. Beta blockers can be used as first-line therapy in the management of hypertension and can be safely combined with diuretics, vasodilators, or both, for a better control of blood pressure. The exact mechanism by which beta blockers decrease blood pressure remains speculative, but they all reduce cardiac output during long-term therapy; drugs with ISA lower cardiac output and heart rate less than do drugs without ISA. Pharmacokinetic properties of beta blockers differ widely; drugs metabolized by the liver have shorter plasma half-lives than drugs primarily excreted by the kidneys. Although many of the side effects of various beta blockers are similar, differences in water and lipid solubility account for a higher incidence of central nervous system side effects with lipid-soluble drugs (such as propranolol and metoprolol) than with hydrophilic drugs (such as atenolol and timolol). The incidence of cold extremities has been reported to be less with drugs with ISA, and the incidence of bronchospasm less with cardioselective drugs. In the management of uncomplicated mild-to-moderate hypertension, all beta blockers are equally effective and produce less troublesome side effects than alternative antihypertensive agents. For effective therapy beta blockers can be used in 2 divided daily doses or even once daily.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of beta 1-adrenoceptor agonism on plasma renin activity in normal men

The contribution of beta 1-adrenoceptors to the regulation of plasma renin activity was investigated in nine healthy sodium-replete volunteers: seven subjects received a cumulative intravenous dose of 75 micrograms/kg prenalterol, a predominant beta 1-adrenoceptor agonist, and two subjects only vehiculum. In the seven actively treated subjects beta 1-adrenoceptor agonism increased (P less than 0.001) systolic intra-arterial pressure by an average of 16 +/- 4 mm Hg and heart rate by 19 +/- 3 beats min. These increases were significantly (P less than 0.04) different from the changes observed in the two control subjects (+ 3 +/- 4 mm Hg and -1 +/- 4 beats/min, respectively). Plasma renin activity, however, tended to decrease in both the actively (-38%) and saline (-28%) treated subjects. Predominant beta 1-adrenoceptor agonism, powerful enough to increase systolic pressure and heart rate does not increase plasma renin activity in supine sodium-replete normal man.

Pindolol: a review of its pharmacology, pharmacokinetics, clinical uses, and adverse effects

Pindolol is a new noncardioselective beta adrenergic blocking agent with intrinsic sympathomimetic activity. In the treatment of mild to moderate hypertension, pindolol provides effective control of blood pressure in a large majority of patients when administered alone or, more commonly, when combined with a thiazide diuretic. Pindolol is approximately as effective as propranolol in the therapy of hypertension, but in some crossover trials central nervous system side effects were more frequent with pindolol. A "ceiling effect" may be observed as dosages are titrated upward above approximately 20 to 30 mg per day, such that further blood pressure reductions may not be achievable. Some patients will exhibit a paradoxical increase in blood pressure with an increase in dosage. In patients who respond to modest doses of pindolol, twice or even once daily dosing is often adequate. This prolonged duration of hypotensive activity, while not suggested by the kinetics of this or similar drugs, is probably common to most beta blockers. Investigations in small numbers of patients with angina pectoris have reported variable but generally beneficial results with pindolol.

Beta-blockers and renal function

alpha-, beta 1- and beta 2-adrenergic receptors in the kidney mediate vasoconstriction, renin secretion and vasodilatation, respectively. Blockade of beta-receptors may therefore be expected to influence renal blood flow and possibly glomerular filtration rate by intrarenal effects as well as by reducing cardiac output and blood pressure. Since the various beta-adrenergic blocking drugs available differ in the degree to which they block beta 2-receptors (cardioselectivity) and also in their intrinsic sympathomimetic activity, they would be expected to have different effects on renal function. The acute administration of beta-blockers usually results in a reduction in effective renal plasma flow and glomerular filtration rate, whether or not the drug is cardioselective or has intrinsic sympathomimetic activity, with the exceptions of nadolol, which has actually increased effective renal plasma flow in some studies and of tolamolol. With chronic oral administration, the non-cardioselective beta-blockers reduced glomerular filtration rate and effective renal plasma flow. The cardioselective drugs do not usually produce significant reductions in glomerular filtration rate or effective renal plasma flow, although small increases in serum urea during treatment do occur. Interestingly, in contrast to findings with intravenous administration, orally administered nadolol produced a slight reduction in glomerular filtration rate in 1 study, so the effect of this agent on renal function under clinical conditions remains uncertain. It seems likely that beta-blockers reduce renal function predominantly by blocking beta 2-receptors in the kidney. To keep area of discussion in perspective, it is important to realise that although there have been isolated reports of serious deterioration in renal function coinciding with beta-blocker treatment, the great majority of reports are of reduction in glomerular filtration rate which are not of clinical significance, even in patients with pre-existing impairment of renal function. The beta-blockers with low lipid solubility-i.e. atenolol, nadolol and sotalol-are not metabolised, and their dose must be reduced in renal failure. Propranolol has active metabolites and its dose must also be reduced slightly in uraemia.

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

1 A survey has been made of the literature on acute and long-term haemodynamic effects of ten different β-adrenoceptor antagonists.

The β-adrenoceptor blockers are: pindolol, practolol, alprenolol, oxprenolol, acebutolol, penbutolol, metoprolol, atenolol, propranolol and timolol. The total numbers of patients included in this review are 396 patients in 41 acute studies and 410 patients in 36 long-term studies.

2 The effects of β-adrenoceptor blockers on the concentrations of plasma noradrenaline have also been reviewed. Ten studies including 110 patients on non-ISA-β-adrenoceptor blockers and eight studies including 116 patients on pindolol are presented.

3 In the acute studies (i.e. 15-90 min) arterial pressure was lowered by 1-7% and in the long-term studies (i.e. 3 days-5 years) by 6-17%.

4 The degree of cardio-depression induced by the various β-adrenoceptor blockers was inversely correlated with their pharmacologically defined quantity of intrinsic sympathomimetic activity (ISA) both in acute and in long-term studies.

5 In the acute studies the increments in peripheral vascular resistance were directly correlated with the degree of cardio-depression. This suggests that a fall in arterial pressure immediately after administration of a β-adrenoceptor blocker is prevented by increased vasoconstrictor nerve activity mediated through the arterial baroreflex.

6 The compensatory response of vascular resistance to cardio-depression was similar for β₁-selective and non-selective blockers, thereby indicating that extra-junctional vascular β-receptors are relatively unimportant for maintaining basal vascular tone.

7 In the long-term studies the correlation between changes in cardiac output and changes in vascular resistance was shifted to a lower level of vascular resistance. This means that the onset of blood pressure reduction during β-adrenoceptor blockade was associated with a fall in vascular resistance at any level of cardiac output. Thus vascular resistance was higher during treatment with a non-ISA-β-adrenoceptor blocker than during treatment with an ISA-β-adrenoceptor blocker.

8 The level of vascular resistance ultimately attained during treatment with the various β-adrenoceptor blockers appears to be inversely related to their effects on plasma renin activity.

9 The concentration of noradrenaline in plasma rose by approximately 30% during treatment with non-ISA-β-adrenoceptor blockers and fell by more than 30% after pindolol.

10 There is evidence that under propranolol, which reduces cardiac output and hepatic blood flow, the plasma noradrenaline clearance is diminished. Since noradrenaline is mainly cleared from the circulation by the lungs and by the liver, and since pindolol has no effect on cardiac output and hepatic blood flow, one may expect the plasma noradrenaline clearance not to be diminished by pindolol.

11 The reported effects of β-adrenoceptor blockers on plasma noradrenaline may indicate that the release of neurotransmitter is diminished, but in the case of non-ISA-β-adrenoceptor blockers this effect is not reflected by a decreased concentration of noradrenaline in plasma, because its clearance is also reduced.

12 The hypotensive effect of β-adrenoceptor blockers appears to be independent of blockade of postjunctional cardiac-β-receptors, juxtaglomerular-β-receptors and extrajunctional vascular β-receptors. This indicates that blockade of β-receptors at other sites (i.e. centrally and/or prejunctionally) is more important.

Two types of hypotensive effect of beta-blocking agents

In anesthetized and immobilized rats, an hour-long continuous intravenous injection of dl-propranolol (PR; 3 mg/kg), pindolol (PI; 1 mg/kg), oxprenolol (OX; 3 mg/kg) or atenolol (AT; 3 mg/kg) invariably resulted in moderate hypotension. When the drug-induced hypotension was plotted against the control arterial pressure (AP), two types of correlation were found. The hypotension induced by PR or PI, both known to accumulate in the brain at a high concentration was positively correlated to the control AP, whereas the hypotension produced by OX or AT, both known to penetrate the blood-brain-barrier poorly, was not. To test the hypothesis that the observed difference was attributable to the presence or lack of sympathoinhibitory action of the drug, the effect of these agents on the renal nerve activity (RNA) was examined. PR or PI diminished the tonic and reflexly evoked RNA, when the evoked RNA was elicited by sciatic nerve stimulation. No such changes were induced by OX or AT. These results demonstrate a modulatory role of sympathoinhibitory effect of beta-blocking agents in their hypotensive action.

Acid phosphatase activity in the aorta of spontaneously hypertensive rats and the effect of various antihypertensive drugs

In an attempt to obtain information about the arterial lysosomal enzymes in hypertension, we biochemically investigated acid phosphatase (Ac-Pase) activity in the aorta of spontaneously hypertensive rats (SHR) and the effects of various antihypertensive drugs. Ac-Pase activity in SHR was always higher than that in age-matched control rats. The enzyme activity tended to increase progressively with advancing age, a tendency which was more pronounced in SHR than in control rats. The aging process expressed by the Ac-Pase activity seems to be accelerated under hypertensive conditions. Antihypertensive drugs such as reserpine, hydrochlorothiazide, hydralazine and propranolol significantly suppressed the rise of blood pressure and decreased the aortic Ac-Pase activity in SHR. In particular reserpine and propranolol lowered Ac-Pase activity more effectively than it did blood pressure. Hypertension as well as catecholamine seem to be involved in the increase in the aortic lysosomal enzyme activity in SHR.

Effect of prenalterol, a beta-1-adrenoceptor agonist, on renin secretion rate in the anaesthetized dog

The effects of the beta-1-adrenoceptor agonist, prenalterol, 20 microgram/kg intravenously on renin secretion rate (RSR), renal haemodynamics and sodium excretion were examined in anaesthetized dogs with innervated or denervated kidneys. In dogs with innervated kidneys, prenalterol increased RSR from 1.1 +/- 0.2 to 7.9 +/- 0.1 units X min.-1 X g-1 (P less than 0.01). Prenalterol did not affect mean arterial pressure, renal blood flow, glomerular filtration rate or sodium excretion. Heart rate was increased by 53 +/- 17 beats/min. (P less than 0.01). The increase in RSR produced by prenalterol was independent of intact renal innervation as RSR increased to the same extent in dogs with denervated kidneys. Pretreatment with the beta-1-adrenoceptor antagonist, metoprolol 0.5 mg/kg intravenously, abolished the increase in RSR produced by prenalterol. These findings suggest that prenalterol directly activates renal beta-1-adrenoceptors to increase RSR.

An investigation into the type of beta-adrenoceptor mediating sympathetically activated renin release in the cat

1 Stimulation of the renal nerves in the cat was previously shown to cause renin release which could be blocked by propranolol. An attempt was made in this study to determine the type of beta-adrenoceptor mediating this response.2 In anaesthetized, unilaterally nephrectomized cats, a comparison was made of the ability of two selective beta-adrenoceptor antagonists to block the tachycardia and hypotension caused by isoprenaline (mediated respectively by beta(1)- and beta(2)-adrenoceptors) and the release of renin caused by renal nerve stimulation.3 Isoprenaline (mean dose of 0.224 +/- 0.022 nmol/kg), increased heart rate by approximately 43 beats/min and decreased mean blood pressure by 47 mmHg. Stimulation of the distal cut ends of the renal nerves, at a rate sufficient to reduce renal blood flow by 30%, resulted in an approximately 150% increase in plasma renin activity.4 Administration of the selective beta(1)-adrenoceptor antagonist, atenolol (0.38 to 11.28 mumol/kg), caused a dose-related inhibition of nerve stimulated renin release and of isoprenaline-induced tachycardia, with no diminution of the vasodepressor response to isoprenaline; in contrast, the selective beta(2)-adrenoceptor antagonist, erythro-DL-(7-methylindan-4-yloxy)-3-isopropylamino-butan-2-ol (ICI 118, 551, 0.03 to 2.86 mumol/kg), caused a dose-related inhibition of the isoprenaline-induced vasodepression without altering the increase in plasma renin activity caused by renal nerve stimulation. Only at the highest dose of ICI 118, 551 was there a reduction of isoprenaline-induced tachycardia, by about 40%.5 The selective inhibition of neurally activated renin release by atenolol but not by ICI, 118, 551 is consistent with the suggestion that the beta-adrenoceptors mediating renin release resemble those in the heart more closely than those in peripheral blood vessels.

Effect of pindolol on blood pressure, plasma renin activity, and catecholamines in hypertensive patients

The effects of 45 mg pindolol daily on blood pressure, heart rate, plasma renin activity, and plasma catecholamines were assessed on 11 hospitalized hypertensive patients. Blood pressure decreased significantly after nine days of treatment, but heart rate remained unchanged. Plasma renin activity was in the same average range before and during treatment, with individual values variably increasing, decreasing, or remaining unchanged. Blood pressure changes were independent from the baseline level of plasma renin activity or the change in renin activity observed during treatment. Plasma epinephrine and norepinephrine levels also remained unchanged during treatment. Lack of change in heart rate and hormonal levels may be attributed to the combined effects of the beta-antagonistic and partial agonistic properties of this agent. Thus, pindolol used as monotherapy at this dose significantly lowered blood pressure, but not to normal levels, with only minimal side effects. Because of its combined adrenergic agonistic and antagonistic effects, it may be a preferable alternative to pure antagonists in selected patients.

Control of canine renin release: macula densa requires prostaglandin synthesis

1. The macula densa mechanism of renin release was functionally isolated in uninephrectomized, anaesthetized dogs by producing renal denervation, beta-adrenoceptor blockade, and maximum renal vasodilation with an infusion of papaverine into the renal artery. 2. A suprarenal aortic clamp was adjusted to reduce renal perfusion pressure by 50% which resulted in a 90% reduction in urinary sodium excretion and a two to threefold increase in plasma renin activity within 10 min. 3. Indomethacin (8 mg/kg) or meclofenamic acid (10 mg/kg) inhibited the rise plasma renin activity produced by the decrease in renal perfusion pressure in this model, although a comparable decrease in urinary sodium excretion was achieved. 4. We conclude that the macula densa mechanism of renin release is blocked by inhibition of prostaglandin synthesis.

Effects of a beta 1-selective adrenergic agonist in normal human volunteers

In healthy volunteers, the effects of prenalterol, a new beta 1-adrenoceptor agonist, on renal hemodynamics, excretory function, plasma-renin-activity, plasma cAMP concentration, and plasma and urinary norepinephrine were studied. Besides an increase in blood pressure, which was adjusted to about 20 mmHg above the resting values, and an increase of heart rate, prenalterol induced only transient decreases of urinary volume and free water clearance and in increase of sodium excretion. The other parameters measured did not change. Thus prenalterol mainly exerts positive inotropic and chronotropic effects and does not affect renal circulation.

beta blockade with pindolol: differential cardiac and renal effects despite similar plasma kinetics in normal and uremic man

Cardiac and renal effects (measured as the reduction in exercise-induced tachycardia and PRA, respectively) and circulating drug concentrations after acute beta blockade with intravenous pindolol were compared between seven normal volunteers and six patients with terminal renal failure. Kinetic parameters were similar in both groups (total body clearance, 450 mg/min), indicating enhanced extrarenal elimination in patients. For any given drug concentration, however, the uremic patients responded to beta blockade with a greater decrease in pulse rate than did normal volunteers (P less than 0.001). Moreover, in the same group, the decrease of PRA was more marked (from 13.3 to 5.7 vs. 3.3 to 1.9 ng/ml/hr) and lasted longer (8 hours and more vs. 2 hours). Plasma aldosterone remained unchanged. These data reveal an increased dependency of both heart rate and renin release on beta adrenergic-mediated mechanisms in uremic man. They also show that kinetic findings in normal subjects cannot always be extrapolated to predict kinetic behavior in disease, and that similar kinetics do not imply similar effectiveness.

Antihypertensive action of beta-adrenoceptor blockade and the renin-angiotensin system

1 The regulation of renin secretion is mediated by way of adrenoceptors. The role of alpha-adrenoceptors remains controversial, whereas it is generally accepted that activation of beta-adrenoceptors stimulates renin and their blockade suppresses renin. 2 Although experimental renin regulation appears to be a beta 2-receptor function, clinical studies suggest that in man it is a beta 1 effect. 3 beta-Adrenoceptor-blocking agents are effective antihypertensive agents, but have variable effects on renin secretion; this variability may be attributable to different degrees of instrinsic partial beta-agonistic activity and/or different receptor or organ selectivity of various compounds. 4 Antihypertensive effectiveness seems unrelated in magnitude or timing to the baseline levels or the changes of plasma renin activity for the majority of beta-adrenoceptor-blocking drugs.

Selective and non-selective beta-blockade in renin release

The effects of two beta-adrenergic receptor blocking drugs, the non-selective propranolol and the beta1selective metoprolol, were studied on hemodynamics and plasma renin activity (PRA) of healthy volunteers in an ergometric exercise test. Oral doses of 160 mg of propranolol and 200 mg of metoprolol were tested against placebo. The drug plasma concentrations were determined. Heart rate and systolic blood pressure were equal and significantly lower during treatment with both active drugs when compared to placebo. The effect of drugs on exercise heart rate was correlated with the logarithm of drug plasma concentration with both propranolol and metoprolol. Propranolol, but not metoprolol, decreased the basal level of PRA. The ergometric exercise induced a significant rise in PRA after placebo but this increase was partially inhibited by the both active drugs. On the basis of these findings it is suggested that in man the basal level of PRA could be decreased mainly by blocking the beta2-adrenoceptors. Instead the exercise induced increase of PRA could be inhibited by blocking the beta1-adrenergic receptors.

The effect of beta-adrenergic blockade on patterns of urinary sodium excretion, blood pressure and plasma renin activity in patients with essential and renovascular hypertension

The effects of beta-adrenergic blockade, using oxprenolol, were studied in plasma renin activity, urinary sodium excretion and blood pressure in ten normal subjects and in 120 patients with essential and renovascular hypertension. Blood pressure was reduced by oxprenolol administration. The hypotensive action of the drug was independent of either the basal plasma renin activity or of the plasma renin activity response. Oxprenolol decreased plasma renin activity in normal subjects and in patients with essential hypertension with normal or high basal plasma renin activity. Patients with low plasma renin activity may show a lack of response to the beta-blockade. In patients with renovascular disease the response of plasma renin activity to oxprenolol was not a discriminant factor between patients cured or not cured by surgery. Some renovascular patients were unresponsive to beta-blockade with oxprenolol.

Effects of prolonged infusion of beta-adrenergic agonists on uterine and umbilical blood flow in pregnant sheep

We have extended our evaluation of the effects of three beta-adrenergic agents in near-term pregnant sheep to include a period of infusion three times longer than previously studied. This extension has provided the following information: (1) Initial depression of uterine blood flow and mean arterial pressure associated with administration of ritodrine or salbutamol abate with time despite continued drug infusion; (2) the uterine hyperemia associated with salbutamol and fenoterol are drug-related rather than postinfusion-related phenomena; (3) increased uterine vascular resistance is found with ritodrine, and decreased uterine vascular resistance occurs with salbutamol and fenoterol.

Prevention by somatostatin of rise in blood pressure and plasma renin mediated by beta-receptor stimulation

The interrelationships of increased plasma renin and elevated blood pressure following acute beta-stimulation by orcipernaline and its prevention by somatostatin was studied in normal man. During somatostatin infusion basal values of renin and blood pressure were unchanged. Following orciprenaline both variables increased significantly. Combination of somatostatin and orciprenaline reduced the rise in plasma renin activity by 49%, mean arterial blood pressure by 21% and heart rate by 19%, compared with beta-stimulation alone. The results indicate that the inhibitory action of somatostatin on plasma renin activity may be mediated via beta-receptors. The lesser increase of blood pressure under somatostatin plus orciprenaline also indicates a possible inhibitory effect of somatostatin on beta-adrenergic receptors.

Effect of a new beta-adrenergic blocker, l-bunolol, on blood pressure and on the renin-aldosterone system

The antihypertensive effect of a new beta-adrenergic receptor blocker, l-bunolol, was evaluated in 11 hospitalized hypertensive patients of whom four belonged to the high-renin, five to the normal-renin, and two to the low-renin subgroup. There was a significant decrease in blood pressure in most patients, often to normal. Moreover, plasma renin levels were nearly always markedly suppressed, and this suppression preceded the fall in blood pressure. While most high and normal renin patients responded, the numbers of patients within each subgroup were too small to correlate the blood pressure responses with changes in renin levels. There was a significant induced decrease in aldosterone excretion, which usually paralleled the renin suppression. Pulse rate was also consistently reduced during treatment. No weight gain was observed, except in one patient who developed overt congestive cardiac failure. No other side effects were recorded. Ii is concluded that l-bunolol is another beta-blocking drug with significant antihypertensive action. It was found to be effective in cases that were resistant to propranolo. It is well tolerated and safe to use, provided that early evidence of fluid retention is sought for and treated immediately.

Antihypertensive and renin angiotensin effects of metolazone with and without propranolol

Renin angiotensin system parameters and blood pressure (B.P.) were followed monthly in patients with essential hypertension on metolazone, 5 mg daily for three months and with added propranolol, 40 to 160 mg, for the subsequent three months. On metolazone alone at three months, sitting B.P. declined from 166/108 +/- 14/11 mm Hg to 145/98 +/- 14/9 mm Hg (P less than 0.005). Plasma renin activity (PRA) increased from 3.9 +/- ng/ml/hr to 10.4 +/- 8.6 ng/ml/hr (P less than 0.005); plasma angiotensinogen did not change. Venous blood angiotensin I and II levels (pg/ml) rose initially but returned toward control values. A significant decline in plasma renin substrate reactivity (PRSr) in index occurred. Propranolol addition caused further lowering of only systolic B.P. and predominantly in the standing position, more marked at one month (40 mg) than at three months (160 mg). No significant further changes were observed in any of the measured parameters of renin angiotensin system, except for a rise in PRSr index concomitant with B.P. elevation at three months. Metolazone-induced changes in B.P. showed significant correlations at three months with changes in PRSr index. It is concluded that during chronic metolazone administration, the overall activity of the renin angiotensin system was diminished or unchanged. Propranolol did not inhibit metolazone stimulated PRA but did cause further decline in B.P. in the first two months, unrelated to renin angiotensin system.

[Effect of the beta-receptor-blocker prindolol on renal hypertension (author's transl)]

Under standardised conditions Prindolol-therapy (3 X 5 mg/die) was carried out in patients with renal hypertension in addition to the preexisting anti-hypertensive treatment during a period of 8 weeks. After administration of Prindolol for 4 and 8 weeks a significant (p less than 0.05) reduction of blood pressure (systolic and diastolic) was observed. 3 weeks after discontinuing the Prindolol-therapy blood pressure rose again, but it clearly remained below pretreatment level. Peak values of blood pressure during the day were markedly lowered. Antihypertensive efficacy was age-related. Lowering of blood pressure occurred in 70% of our patients. There existed no relation between plasma-renin-level and reactivity of the patients to the antihypertensive effect of Prindolol. Renal function (creatine-clearance) did not alter significantly by Prindolol-treatment.

[Cyclic AMP and plasma renin activity in renal vein blood after amitryptiline, theophylline, furosemide and beta adrenergic blocking substances (author's transl)]

The influence of amitryptiline, theophylline and furosemide on the concentration of cyclic-AMP and plasma renin activity (PRA) was investigated in renal vein plasma. Additionally, the stimulating effect of furosemide on the PRA after application of the beta-adrenergic receptor antagonists propranolol and practolol and the cyclic AMP concentration in the plasma were measured. All drugs were given intravenously. After amitryptiline cyclic-AMP concentration increased about 1.5-fold compared with the basal value,PRA was not altered. After theophylline cyclic-AMP concentration increased about 1.2-fold, PRA 2.0-fold compared with the basal value, PRA was not altered. After theophylline cyclic-AMP concentration increased about 1.2-fold, PRA 2.0-fold coa increased within 7 min and no further increase was observed till the 15th min. After practolol cyclic-AMP concentration and PRA decreased about 20% compared with the basal value within 10 min. The stimulating effect of subsequently applied furosemide on PRA was not altered, but the cyclic-AMP concentration was not changed in this time by furosemide. After propranolol cyclic-AMP concentration and PRA decreased about 20% compared with the basal value. The cyclic-AMP concentration was not influenced by the following furosemide application, in agreement with the findings after practolol, however, PRA could be stimulated only in 36% of these patients under beta-receptor blockade. Our results show that changes of the concentrations of cyclic-AMP and of PRA are independent of each other. An elevated intracellular cyclic-AMP level due to the inhibition of phosphodiesterase is as a single factor unable to stimulate renin release. Our results give no evidence of a direct involvement of the adenylcyclase-system in the mechanism of renin release. The effect of propranolol and practolol on the basal value of PRA and cyclic-AMP is equal. The different influence of 10 mg propranolol and 20 mg practolol on the stimulating effect of 40 mg furosemide on the PRA can be interpreted as a dosage problem.

Beta-adrenergic receptor blocking drugs in spontaneous hypertension

Eleven beta-adrenergic receptor blocking agents and derivatives were evaluated for their ability to affect systolic arterial blood pressure and pulse rate in unanesthetized, male spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto (WKY) controls. Animals ranged from 7 to 76 weeks of age. The subcutaneous injection of 5 and 45 mg/kg metoprolol in 52 to 64 week old SHRs and 45 mg/kg twice a day to 26 to 29 week old SHRs produced a significant decrease in blooc pressure. The subcutaneous injection of pindolol (0.1 and 1.0 mg/kg) produced a greater and more consistent depressor effect in mature SHRs. The subcutaneous administration of sotalol (100 mg/kg) and alprenolol (20 mg/kg) resulted in a depressor action which was significant 120 minutes after injection of the drug. In the doses used, propranolol, oxprenolol, 4-hydroxypropranolol and K9-1366 produced pressor effect in SHRs. Propranolol did not cause this pressor effect in prehypertensive (seven week old) SHRs. Practolol, dextro-propranolol and KO-1313 had no effect on blood pressure in the doses used. Propranolol, pindolol, metoprolol, dextro-propranolol, 4-hydroxypropranolol, practolol, oxprenolol, KO-1366 and KO-1313 produced no significant effects on blood pressure in normotensive WKY controls in the doses tested. Placing oral doses of 160 mg/kg/day of metoprolol in the drinking water for seven days significantly lowered blood pressure in 14 week old SHRs previously exposed to ineffective doses of 77 mg/kg/day for 24 days. The administration of oral doses of oxprenolol (40 mg/kg/day) in drinking water for three weeks had a slight but insignificant pressor effect. Smaller doses of metoprolol (15 and 39 mg/kg/day for three to four weeks) and practolol (70 to 85 mg/kg/day for two weeks) had no effect on 52 week old SHRs. Oral doses of pindolol, metoprolol, practolol and oxprenolol had no significant effect on blood pressure in WKY controls. There was no clear relationship between the effects of the drugs on blood pressure and their ability to affect the pulse rate. Similarly, there did not appear to be any consistent relationship between the potency of the beta-blocking drug and the blood pressure lowering action. In addition, neither cardioselective beta-blockade nor sympathomimetic properties allowed the prediction of blood pressure responses to the administration of those agents possessing these features. Although SHRs provide a valuable model of human essential hypertension, the variable effects reported here and elsewhere in the literature require caution as to the applicability and usefulness of testing and evaluating beta-adrenergic blocking drugs for theri potential anti-hypertensive effects in this particular form of experimental hypertension.

Is the adrenergic control of renin release dominant in man?

Two beta-blocking agents with different properties were used to define the adrenergic component of the renin release which follows orthostasis. Five normal young subjects were tilted to 85 degrees for 30 min on four separate occasions. In two control studies the release of renin, as indicated by changes in plasma-renin activity, was highly reproducible. The effects of intravenous oxprenolol and intravenous propranolol, were then compared under the same experimental conditions. Oxprenolol attenuated the renin response in all subjects without completely abolishing it. Propranolol completely abolished the renin response. The difference in the ability of these agents to suppress renin release may be related to the presence (oxprenolol) or absence (propranolol) of intrinsic sympathomimetic activity. The increased rate of renin release in orthostasis seems to be mediated entirely by the adrenergic nervous system.

[Interrelations between blood pressure, blood volume, plasma renin and urinary catecholamines during beta-blockade in essential hypertension (author's transl)]

Studies in 55 patients with benign essential hypertension showed that the beta-blockers bufuralol (22 patients) and propranolol (33 patients) at a dose ratio of 1:4, possess comparable antihypertensive efficacy despite different properties regarding intrinsic sympathomimetic activity. Beta-blocker-monotherapy normalized blood pressure ( less than 140/90 mm Hg) in one fourth of the patients. Body weight and plasma and blood volumes remained unchanged during beta-blockade of four to six weeks duration, the mean plasma potassium was slightly increased. The inhibition of plasma renin activity (PRA) was more pronounced with propranolol (-69%) than with bufuralol (-47%). Wirth both beta-blockers decreases in blood pressure correlated inversely with pre-treatment PRA (p less than 0.05). Propranolol-induced changes in blood pressure correlated also with associated changes in PRA (p less than 0.005); in contrast, no such relationship was observed with bufuralol. The blood pressure effects of bufuralol, however, correlated significantly with changes in urinary noradrenaline excretion (r=0.41; p less than 0.05). Patient sub-groups with low, normal or high pre-treatment PRA in the average showed a comparable pattern of pre-treatment noradrenaline excretion and patients with normal renin levels exreted more adrenaline than those with low renin levels (p less than 0.001). These data are consistent with the concept that in untreated essential hypertension PRA may be an index of adrenergic activiity, the latter representing an important determinant of blood pressure response to beta-blockade. The blood pressure lowering effects of bufuralol in benign essential hypertension seem to be independent of renin and may be related, at least partly, to diminished free peripheral noradrenaline levels.

Renin, aldosterone and arterial pressure responses to acute beta-adrenergic receptor blockage in hypertensive patients

The effect of acute (intravenous) beta-adrenergic blockade with propranolol or pindolol on arterial pressure (BP), plasma renin activity (PRA), and plasma concentration of aldosterone (PA) was evaluated in 20 essential hypertensive men. BP, PRA and PA were determined during continuous recumbency over-night (8 p.m. to 6 a.m.) every 30 min. Two groups of patients were observed. Patients of group 1 exhibited a characteristic day-night rhythm of PRA with low values before midnight and large increases early in the morning. Conversely, no rhythm and very low PRA values were observed in patients of group II. BP was higher in group II than in group I. In group I following intravenous propranolol or pindolol, BP fell within minutes and levels as well as rhythms of PRA were converted to those of group II without treatment. In group II day-night profiles of PRA and BP remained unchanged. Rhythm and concentration of PA in the two groups were not influenced by either drug. In 4 patients of group I infusion of angiotensin II inhibitor did not lower BP. The observations suggest that in the two groups dissimilarities in rhythms of PRA as well as in BP responses to beta-blockade may reflect differences in neuro-adrenergic tone.

Acute and long-term studies of the mechanisms of action of beta-blocking drugs in lowering blood pressure

The antihypertensive effect of intravenous (acute) and oral (long-term) beta-adrenergic blockade with propranolol or pindolol was evaluated in 46 male patients with either borderline (group I; 23 patients) or sustained (group II; 23 patients) essential hypertension. Arterial pressure, plasma renin activity and plasma concentration of aldosterone were determined during continuous recumbency overnight every 30 minutes before and after treatment. Patients of group I exhibited a marked variation of their recumbent plasma renin activity with relatively low values before midnight and large increases early in the morning. In contrast, low plasma renin activity values and only minimal fluctuations in renin were observed in patients of group II. Plasma renin activity had a consistent relationship with blood pressure both after acute (r = 0.79) and long-term (r = 0.4) beta-blockade. In four patients of group I, who had high plasma renin activity and had responded to intravenous propranolol, infusion of angiotensin II inhibitor did not lower pressure. In group I following beta-blockade, day-night profiles of renin were similar to those observed in group II before treatment. Thus in this latter subgroup, low renin profiles might reflect reduced beta-adrenergic activity. Acute as well as long-term beta-blockade consistently eliminated the day-night rhythm of plasma renin activity, but it did not change rhythm of plasma concentration of aldosterone. Plasma concentration of aldosterone was lower in group II but appeared to be inappropriately high relative to renin levels. These observations suggest that in hypertensive patients classified according to blood pressure and recumbent plasma renin activity profiles a significant relationship exists between changes in plasma renin activity and arterial pressure responses. Thus, patients with high renin levels respond better to treatment than patients with low renin levels. We conclude that in the patients studied, sympathetic nervous system activity mainly determined renin levels as well as antihypertensive effectiveness of the beta-blocking drugs.