Current management of inherited arrhythmia syndromes associated with the cardiac ryanodine receptor

PURPOSE OF REVIEW

Gain-of-function variants in the gene encoding the cardiac ryanodine receptor ( RYR2 ) are associated with catecholaminergic polymorphic ventricular tachycardia (CPVT). The exercise stress test (EST) has long been fundamental in diagnosis and management, but recent work has further explored its role. A new entity termed calcium release deficiency syndrome (CRDS) has been associated with loss-of-function RYR2 variants and a different arrhythmic phenotype.

RECENT FINDINGS

Standard EST is not perfectly reproducible with regards to provocation of arrhythmia in CPVT. A newly described burst EST protocol may be more sensitive in this regard. Nadolol is the most effective beta blocker in CPVT, though arrhythmic events remain frequent and dual therapy with flecainide and/or left cardiac sympathetic denervation may add protection. A recent report renews debate regarding the use of implantable defibrillator therapy in CPVT. CRDS is characterized by later age of presentation, normal/near normal EST, and ventricular arrhythmia induced by a novel ventricular stimulation protocol.

SUMMARY

Burst EST may aid in the diagnosis and management of CPVT. Nadolol is the preferred beta blocker in CPVT, and consideration should be given to early dual therapy. CRDS should be suspected in patients with arrhythmic events, rare RYR2 variants, and a phenotype inconsistent with CPVT.

A HPLC-MS/MS method for the determination of Nadolol in rat plasma: Development, validation, and application to pharmacokinetic study

A sensitive validated method has been developed for the quantification of Nadolol in rat plasma by high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) using deuterated Nadolol (Nadolol D9) as internal standard (IS). The liquid-liquid extraction method using ethyl acetate was employed for the sample pretreatment. The separation was achieved on the Agilent Zorbax XDB C18 column (150  mm  ×  4.6  mm ID., 3.5  μm). The column temperature was controlled at 30°C. The components were eluted by using mobile phase A (10  mM ammonium formate) and mobile phase B (acetonitrile) in the ratio of 20:80  v/v with a flow rate of 0.5  mL/min. And 15  μL aliquot was injected in an isocratic elution mode with a total run time of 2.5  min. The multiple reactions monitoring transitions, m/z 310.20/254.10 for Nadolol and IS 319.20/255.00 were selected to achieve high selective analysis. The method exhibited great selectivity and linearity over the concentration range of 6 to 3000  ng/mL. The lower limit of quantification was found to be 6  ng/mL. The developed method proved acceptable results on selectivity, sensitivity, precision, accuracy, and stability studies as per Food and Drug Administration guidelines. This HPLC-MS/MS assay was successfully applied to get the pharmacokinetics parameters in rat plasma.

Stability of Extemporaneously Compounded Nadolol 10-mg/mL Suspension in Oral Mix in Glass and Plastic Bottles and Plastic Syringes

An oral liquid formulation of nadolol, which is required for administration to patients who cannot swallow intact tablets, is not commercially available. The objective of this study was to evaluate the stability of nadolol 10 mg/mL prepared in Oral Mix vehicle and stored in amber glass, amber polyethylene terephthalate, or amber polyvinyl chloride for 91 days at 4ÆC and 25ÆC; and polypropylene oral plastic syringes at 25ÆC only. Three separate batches of nadolol suspension 10 mg/mL were prepared with Oral Mix. Of the suspension, 50-mL aliquots were stored in 100-mL bottles (amber glass, amber polyethylene terephthalate, or amber polyvinyl chloride). Half of the bottles from each container type were stored at 25ÆC and the other half at 4ÆC. On study days 0, 2, 7, 14, 21, 28, 42, 56, 72, and 91, nadolol concentration was determined using a reverse-phase, stability-indicating liquid chromatographic method from samples drawn from each type of container at each temperature. Oral syringes (3 mL), filled with 2 mL of suspension, were stored at 25ÆC and tested on days 0, 2, 7, 21, 42, and 91. The concentration of nadolol 10 mg/mL in Oral Mix in all study samples from bottles and oral syringes remained within 3.5% of the initial concentration. Based on the fastest degradation rate with 95% confidence, on day 91, between 99% to 100% and 98% to 100% remained in suspensions stored in bottles at 25ÆC and 4ÆC, respectively. Oral syringes at 25ÆC had 94% remaining on day 91. Multiple linear regression analysis demonstrated that the percent remaining was related to study day and container, but not temperature. On day 91, nadolol 10 mg/mL oral suspensions prepared with Oral Mix and stored in all bottle types at 4ÆC will retain more than 98% of the initial concentration compared to 99% at 25ÆC and only 94% when stored in oral syringes.

Vigorous exercise mobilizes CD34+ hematopoietic stem cells to peripheral blood via the β2-adrenergic receptor

Acute dynamic exercise mobilizes CD34+ hematopoietic stem cells (HSCs) to the bloodstream, potentially serving as an economical adjuvant to boost the collection of HSCs from stem cell transplant donors. The mechanisms responsible for HSC mobilization with exercise are unknown but are likely due to hemodynamic perturbations, endogenous granulocyte-colony stimulating factor (G-CSF), and/or β2-adrenergic receptor (β2-AR) signaling. We characterized the temporal response of HSC mobilization and plasma G-CSF following exercise, and determined the impact of in vivo β-AR blockade on the exercise-induced mobilization of HSCs. Healthy runners (n = 15) completed, in balanced order, two single bouts of steady state treadmill running exercise at moderate (lasting 90-min) or vigorous (lasting 30-min) intensity. A separate cohort of healthy cyclists (n = 12) completed three 30-min cycling ergometer trials at vigorous intensity after ingesting: (i) 10 mg bisoprolol (β1-AR antagonist); (ii) 80 mg nadolol (β1 + β2-AR antagonist); or (iii) placebo, in balanced order with a double-blind design. Blood samples collected before, during (runners only), immediately after, and at several points during exercise recovery were used to determine circulating G-CSF levels (runners only) and enumerate CD34+ HSCs by flow cytometry (runners and cyclists). Steady state vigorous but not moderate intensity exercise mobilized HSCs, increasing the total blood CD34+ count by ∼4.15 ± 1.62 Δcells/µl (+202 ± 92%) compared to resting conditions. Plasma G-CSF increased in response to moderate but not vigorous exercise. Relative to placebo, nadolol and bisoprolol lowered exercising heart rate and blood pressure to comparable levels. The number of CD34+ HSCs increased with exercise after the placebo and bisoprolol trials, but not the nadolol trial, suggesting β2-AR signaling mediated the mobilization of CD34+ cells [Placebo: 2.10 ± 1.16 (207 ± 69.2%), Bisoprolol 1.66 ± 0.79 (+163 ± 29%), Nadolol: 0.68 ± 0.54 (+143 ± 36%) Δcells/µL]. We conclude that the mobilization of CD34+ HSCs with exercise is not dependent on circulating G-CSF and is likely due to the combined actions of β2-AR signaling and hemodynamic shear stress.

Effectiveness of low-dose nadolol for ventricular arrhythmias

To determine the minimal effective dose of nadolol to suppress frequent ventricular premature complexes (VPCs), 23 patients with at least 30 VPCs/hour on 2 baseline 24-hour Holter recordings were studied. The initial dose of nadolol was 10 mg/day orally, and this dose was doubled at weekly intervals until arrhythmia suppression was achieved, adverse effects appeared, or a maximal dose of 160 mg/day was reached. After each dose level a 24-hour ambulatory Holter monitor was recorded. A pharmacokinetic trial was conducted in patients who responded to nadolol treatment. Frequent VPCs were suppressed at least 75% by nadolol in 11 of 23 patients (48%) and the minimal effective dose was 10 mg/day in 3 patients, 20 mg/day in 4, 40 mg/day in 3 and 80 mg/day in 1 patient. At these doses, minimal steady-state levels of nadolol in serum (Cmin) ranged from 3.9 to 47.0 ng/ml, and these serum concentrations were proportional to the oral dose of nadolol (r = 0.753, p less than 0.001). No relation, however, was observed between Cmin levels and percent reduction of VPCs. Cmin and heart rate changes were comparable between responders and nonresponders, suggesting that the degree of beta blockade was similar between these 2 groups. Adverse reactions were noted in 6 patients, and 2 had an asymptomatic increase in the frequency of VPCs and 1 patient an increase in beats of ventricular tachycardia. This study details the importance of selecting an individualized dose for nadolol for control of ventricular arrhythmias; in more than half of the patients doses of 20 mg/day or less were effective.

Antiarrhythmic drugs and the modulation of autonomic control of heart rate in rabbits

A model of the components of autonomic control of heart rate was developed and used for the evaluation of quantitative contribution of sympathetic and vagal tone to cardiac function. In conscious rabbits, sequential inhibition of muscarinic and beta receptors was produced and the relative contributions of vagal and sympathetic tone were characterized. Based on the model, the magnitude of presynaptic interaction between the vagal and sympathetic nerve endings was evaluated. From data in the literature, similar analysis of the control of heart rate was performed for the rat, dog, and human subject and compared with that of the rabbit. The results show that the resting rabbit heart is under less vagal tone than sympathetic tone as compared with other species. The effects of acute administration of amiodarone on the sympathetic and parasympathetic control of heart rate as well as intrinsic heart rate were investigated. Amiodarone decreased the heart rate, which resulted from a direct effect on the sinoatrial (SA) node. In addition, it attenuated the vagal as well as the sympathetic effects on the SA node. The effect on vagal component was greater. Further, the effects of other antiarrhythmic drugs on the electrocardiographic PP and PR intervals were studied. The usefulness of this model for the analysis of the effects of antiarrhythmic drugs is presented.

Long-acting beta-adrenergic antagonists as preparation for surgery in thyrotoxicosis

This report describes our experience with 12 patients with thyrotoxic Graves' disease who were prepared for thyroidectomy using only a long-acting orally administered beta-adrenergic blocking agent (nadolol or atenolol); iodides were not used. This form of preparation proved to be very effective, fast acting, and economical. It permitted rapid preparation of patients for surgery and resulted in excellent control of the manifestations of hyperthyroidism in the perioperative period. The surgery was relatively easy and bloodless, and there were no operative complications. We recommend that these long-acting beta-adrenergic blocking agents be considered as the preferred medication for the preparation of thyrotoxic patients for surgery.

Effects of nicotine on body weight, food intake and brown adipose tissue thermogenesis

Chronic treatment with nicotine results in reduced body weight gain without a change in food intake. To evaluate the role of brown adipose tissue (BAT) thermogenesis in this effect of nicotine, male Sprague-Dawley rats were chronically treated (3X daily, IP) over a 14 day period with either saline, 0.8 mg/kg nicotine, 10 mg/kg caffeine or a combination of 0.8 mg/kg nicotine and 10 mg/kg caffeine and were pretreated (once daily) with either saline or 20 mg/kg nadolol, a long-acting beta-adrenergic receptor blocker. Nicotine significantly reduced body weight gain but not food intake and nadolol did not reverse the effect of nicotine on body weight gain. To evaluate whether nicotine induces BAT thermogenesis, rats were injected IP with either saline or 0.8, 1.2 or 1.6 mg/kg nicotine hydrogen tartrate, with 5 mg/kg dl-phenylpropanolamine (dl-PPA) or with a combination of 0.8 mg/kg nicotine and 10 mg/kg caffeine with interscapular BAT (IBAT) temperatures recorded for 30 minutes after injection. No dose of nicotine produced a change in IBAT temperature whereas a combination of caffeine and nicotine produced a temperature increase in IBAT (0.95 degree C) 63% of that induced by 5 mg/kg dl-PPA. These data suggest that changes in body weight gain induced by nicotine treatment are not the result of an action of nicotine on BAT thermogenesis.

Effect of nadolol on liver haemodynamics and function in patients with cirrhosis

Beta-adrenoceptor blockers used in the medical management of portal hypertension decrease liver blood flow. The sporadic onset of hepatic encephalopathy during propranolol treatment was ascribed to this decrease. The aim of the present study was to evaluate the effect of chronic treatment with nadolol on liver blood flow and liver function. Nadolol, a non-cardioselective beta-adrenoceptor blocker, has been reported to be as powerful as propranolol in decreasing portal pressure. Before and after 1 month of treatment with nadolol at a dose reducing heart rate by 25%, in 15 cirrhotic patients with portal hypertension, the following parameters were determined: hepatic venous pressure gradient, hepatic blood flow, galactose eliminating capacity, aminopyrine metabolic activity, ICG clearance and intrinsic hepatic clearance. Hepatic venous pressure gradient and hepatic blood flow were decreased by nadolol. However liver function was not affected by the drug. We conclude that, despite a lowered hepatic blood flow, liver function is not affected by 1 month of nadolol treatment.

Influence of beta blockade and intrinsic sympathomimetic activity on hemodynamics, inotropy and respiration at rest and during exercise

The degree of intrinsic sympathomimetic activity (ISA) is reported to influence the effects of beta blockade at rest, but the effects during exercise are not well documented. Heart rate, blood pressure and left ventricular (LV) function (as assessed by systolic time intervals) were measured at rest and during upright bicycle exercise as well as with flow-volume spirometry at rest in 13 healthy volunteers. The measurements were performed before and 4 and 24 hours after a single oral dose of pindolol (10 mg), nadolol (80 mg) and acebutolol (400 mg) in a double-blind, randomized, crossover manner. All drugs reduced heart rate, but nadolol had the most pronounced and longest bradycardic effect at rest. Diastolic blood pressure was only slightly influenced by the drugs, whereas systolic pressure was significantly lower compared with control values, especially during exercise (p less than 0.001). Neither preejection period (PEP) nor LV ejection time (LVETc) was changed at rest after pindolol, but PEP increased and LVETc decreased significantly after nadolol (p less than 0.05 for PEP and p less than 0.01 for LVETc) and acebutolol (p less than 0.05 for both). During exercise, PEP and LVET were significantly longer after all 3 drugs compared with control values. Only nadolol, which lacks ISA, significantly decreased expiratory flow values (p less than 0.05). Thus, unlike the other beta blockers, pindolol (with strong ISA) did not depress LV function at rest, while during exercise all 3 beta blockers had equal adverse effects. The degree of ISA appears to be important in determining the hemodynamic effects of beta-blocking drugs.

Is low-dose hydrochlorothiazide effective?

In a double-blind crossover study, 13 patients with pretreatment diastolic blood pressure between 95 and 109 mm Hg received nadolol, 80 mg/day, plus placebo of hydrochlorothiazide and nadolol, plus three different doses of active hydrochlorothiazide. Patients remained on each active regimen for 3 weeks, with an intervening placebo period of 2 to 4 weeks. With 12.5 mg of hydrochlorothiazide daily plus nadolol, there was no greater reduction of blood pressure than with nadolol alone. A dose of 25 mg of hydrochlorothiazide was associated with a significantly greater decrease in systolic but not diastolic pressure, as compared with nadolol alone. A significantly greater reduction in both systolic and diastolic blood pressure was obtained only with the 50 mg/day dose of hydrochlorothiazide. Extension to 6 weeks of treatment with 12.5 mg/day failed to lower the blood pressure more than the level seen at 3 weeks. These results suggest that in combination with nadolol, 12.5 mg of hydrochlorothiazide per day has no significant antihypertensive effect. There was no evidence of a flat dose-response curve in the daily dose range of 12.5 to 50 mg. For most patients, a dose of 50 mg of hydrochlorothiazide was required to lower both systolic and diastolic blood pressure significantly below the level obtained with nadolol alone.

Beta-adrenergic blockers for the control of aggressive behaviors in patients with chronic schizophrenia

The authors conducted a chart review to determine the effect of beta blockers on chronic assaultiveness in seven patients with chronic schizophrenia. Six of the patients showed improvement. Four of the seven showed a greater than 70% decrease in actual assaults.

Minoxidil, nadolol, and a diuretic. Once-a-day therapy for resistant hypertension

We tested a once-a-day antihypertensive regimen using minoxidil, nadolol, and a diuretic in 55 patients with resistant hypertension. Forty-seven patients had evidence of end-organ damage. Twelve had mild renal insufficiency (serum creatinine concentration, 2.5 +/- 0.3 mg/dL). In 34 patients, treatment with nadolol and a diuretic was started with minoxidil added one to four weeks later. In the remainder, minoxidil, nadolol, and a diuretic were begun simultaneously because of severe hypertension. Initial supine and standing blood pressure (BP) in the 55 patients were 186 +/- 4/111 +/- 2 and 180 +/- 4/108 +/- 2 mm Hg, respectively. After 7 +/- 1 weeks, BP was controlled in 46 patients (84%) with the supine and standing BP reduced to 140 +/- 3/80 +/- 1 and 134 +/- 3/80 +/- 1, respectively. In six patients, BP was controlled but intolerable side effects occurred, making the regimen therapeutically successful in 40 patients (73%). The BP remained controlled during a follow-up of 43 +/- 5 weeks. In 31 patients, BPs measured 24 hours after the last dose were not different from random measurements. Mean serum creatinine levels remained stable in the 12 patients with renal insufficiency.

Comparison of four beta-blockers as assessed by 24-hour ECG recording

beta-Blockers are used as if they were equivalent. With ECG recordings in 42 patients we investigated the effect on sinus heart rate of four beta-blockers given at three successive daily doses. Heart rate was dose-dependently decreased by all drugs except acebutolol, the effect of which decreased at a higher dosage. The maximal effects of metoprolol, nadolol, and propranolol were similar but the drugs differed in potency (dosage producing 50% of maximal effect, calculated from the dose-effect relationships; nadolol, 0.3 mg/day; metoprolol, 120 mg/day; propranolol, 47 mg/day). Similar relationships were found with drug plasma concentrations (concentration producing 50% of maximal effect: nadolol, 3.5 ng/ml; metoprolol, 21 ng/ml; propranolol, 36 ng/ml) and with supine or upright heart rates and blood pressures. However, the drugs were not equivalent: In addition to its greater potency, nadolol differed from propranolol and metoprolol in the slope of its dose-response curve. We conclude that beta-blockers can be compared by ECG recordings and that nadolol is different from the other beta-blockers without intrinsic sympathomimetic activity.

Effects of nadolol on systemic and renal hemodynamics in patients with renoparenchymal hypertension and various degrees of renal function

It has been shown that renal hemodynamic changes following the decrease in cardiac output (CO) after therapy with beta-blockers may affect glomerular filtration rate (GFR), therefore limiting the effectiveness of these drugs; obviously more serious effects might be expected in nephropathic patients with previously reduced renal function. Recent clinical studies have demonstrated that nadolol, a non-cardioselective beta-blocker, preserves the renal blood flow (RBF) and the GFR. In this study, the drug was administered alone (80 mg once daily) for 2 months to 9 male renal parenchymal hypertensive patients with normal or moderately reduced renal function. Systemic and renal hemodynamics, plasma volume (PV), plasma renin activity (PRA) and urinary aldosterone excretion (UA) were evaluated before and after treatment. As blood pressure (BP) fell so did the cardiac index (4.27 +/- 1.05 l/min/m2 to 3.14 +/- 0.48 p less than 0.01), while the peripheral resistance index (TPRI) rose slightly (2257 +/- 658 to 2459 +/- 498 p = NS). No change in PV, RBF, GFR and renal vascular resistance was observed. An increasing trend in PRA (0.81 +/- 0.56 to 1.27 +/- 0.95 ng/ml/h) and no change in UA were observed. Our data show that nadolol was both well tolerated and effective in lowering BP, that it caused systemic hemodynamic alterations similar to those described for other beta-blockers, and preserved RBF and GFR also in renal hypertensive patients with reduced non-azotemic renal function.

A toxicological review of beta-adrenergic blockers

The use of various beta-adrenergic blockers has become extensive as they have been found to be efficacious in the treatment of a number of cardiovascular problems including cardiac arrhythmias, angina pectoris, and hypertension. The widespread and chronic use of these drugs has generated a concern for their potential chronic toxicity. Eighteen beta-adrenergic blockers have been reviewed and the available literature pertaining to their potential carcinogenicity, mutagenicity, and teratogenicity has been summarized and compared.

Effects of bucumolol, nadolol and nifenalol on maximum upstroke velocity of action potential in guinea pig papillary muscles

The effects of bucumolol (BUC), nadolol (NAD) and nifenalol (NIF) on contractile forces and on action potentials (APs) were investigated in isolated guinea pig atrial and papillary muscles, respectively. Log 1/ED40 values for the negative inotropic effects of these drugs were 0.097, 10 and 0.74 mmol/l in this order. BUC (50 mumol/l), NAD (0.5 mmol/l) and NIF (0.2 mmol/l) produced about 60, 20 and 20% reduction of Vmax at 1 Hz. The frequency-dependent reductions at these and higher concentrations were greatest for BUC, intermediate for NAD and least for NIF. These potencies at certain frequencies were, as a whole, consistent with log P-potency relationship established in our previous papers (Harada et al. 1981; Ban et al. 1985). The reductions of Vmax in APs in response to premature stimuli during basic stimuli at the rate of 0.25 or 0.027 Hz decayed exponentially during diastolic intervals (DI). The time constants of these decay process (tau) estimated by linear and nonlinear regression analyses and by eye were 12.2-9.6 s for BUC (50-100 mumol/l) and 2.9-4.8 s for NAD (1-2 mmol/l) and 57-87 ms for NIF (0.2-1 mmol/l). In terms of the molecular weight (MW)-log tau relationship (Ban et al. 1985), these tau values are within the 95% fiducial limit for BUC and NAD and deviated from the lower fiducial limit for NIF. The frequency-dependent reductions of Vmax by these drugs were explained in terms of a function of tau and the intercept Ao. Based on the study made by Cohen et al.(ABSTRACT TRUNCATED AT 250 WORDS)

[Regression of left-ventricular myocardial hypertrophy in patients with hypertension during long-term treatment with beta-adrenergic blockaders]

Thirty-nine patients with second-stage essential hypertension were treated with Beta-adrenoblockers of different classes for 2.5 to 3 years. Two groups of patients were distinguished: 23 patients showing a regression of left-ventricular myocardial weight (group 1) and 16 patients without such developments (group 2). A significant decrease in arterial blood pressure (by 20-24%) and heart rate (by 15 to 18%) was recorded in both groups. Total peripheral resistance was changed insignificantly in group 1 and by 9.7% (p less than 0.05) in group 2. The end diastolic volume decreased by 5.4% (p less than 0.05) in group 1, and increased by 4.7% (p less than 0.05) in group 2. The end systolic volume decreased by 10.6% (p less than 0.05) in group 1 and increased by 5% (p greater than 0.1) in group 2. Myocardial contractility declined significantly in both groups (by 9.5% and 10.6%, respectively). Intramyocardial tension dropped by 13-20% (p less than 0.001) in both groups. Therefore, the regression of left-ventricular myocardial hypertrophy was shown to have a favorable effect on cardiac function.

Effects of amrinone on contraction and K+-induced contracture of normal and subacutely failed cat ventricular muscle

Normal right ventricular muscles and similar preparations obtained from cats with signs of subacute right ventricular failure (RVF) (3 to 14 days after pressure overload induced by pulmonary artery coarctation) were studied during stimulation (at 0.5 Hz) and exposure to high-K+ Tyrode's solution. Twitch force, rate of force development (dP/dt), and rate of relaxation (-dP/dt) were significantly lower in RVF muscles compared with control muscles; duration of the twitch was significantly longer. Time to peak force was unchanged. Amrinone (5.3 x 10(-4)M) increased twitch force and dP/dt in normal muscle; however, the drug had no significant effects on twitch force and dP/dt in RVF muscles. Also unlike its action in control muscle, duration of the twitch was reduced by amrinone in failed muscle. Amrinone reduced K+ contracture force similarly in control and RVF muscle. In control and RVF muscles, isoproterenol (1.0 x 10(-6)M) significantly increased twitch force and dP/dt and reduced K+ contracture, while ouabain increased twitch force, dP/dt, and K+ contracture. The differential effects of amrinone on RVF and control muscles may reflect cellular defects associated with experimental ventricular failure.

Renin and beta-blockade: prorenin and aldosterone may explain the controversy

The role of the renin-aldosterone system in predicting the hypotensive effect of beta-blockade is controversial. We have measured blood pressure, heart rate, plasma active renin, prorenin and aldosterone in 44 hypertensive patients before and after 18 weeks treatment with either nadolol or metoprolol in a double blind randomized study. Prorenin increased and active renin decreased with treatment, total renin and aldosterone remaining unchanged. After beta-blockade the correlation between active renin and prorenin improved from p less than 0.025 to p less than 0.001, and both variables attained a correlation with aldosterone. There was a weak correlation between the reduction in diastolic pressure and both pretreatment active renin and pretreatment prorenin (p less than 0.05). However, using a multiple regression analysis there was a highly significant correlation between the combination of the pretreatment values of active renin, prorenin and aldosterone and the reduction in diastolic pressure with both nadolol (p less than 0.001) and metoprolol (p less than 0.003). This indicates that the combination of active renin with prorenin and aldosterone is a reliable guide to the hypotensive effects of beta-blockade and that the failure to detect this in previous studies is most likely due to errors in the measurement of renin.

Effect of a long acting beta-adrenoceptor blocker on diurnal variation of cardiac dysrhythmias

To investigate circadian variation of cardiac arrhythmias ambulatory electrocardiogram monitoring was carried out before and after one week's treatment with a long acting beta-adrenoceptor blocker, nadolol, in 26 patients who presented with symptoms attributable to arrhythmias. Analysis of the 24 hour profile of premature ventricular contractions showed a significantly (P less than 0.05) higher frequency during midday to midnight than between midnight and midday. The frequency of supraventricular tachycardia was significantly (P less than 0.05) higher during the periods from 12.00 hours to 16.00 hours (11.0 +/- 12) and 16.00 hours to 20.00 hours (11.3 +/- 11) than during the periods of 00.00 hours to 04.00 hours (3.6 +/- 3) and 04.00 hours to 08.00 hours (6.0 +/- 8). The period of the highest incidence of all arrhythmias was between 16.00 hours to 24.00 hours, and that of lowest during the period between 04.00 hours to 12.00 hours (P less than 0.01). After one week's treatment with nadolol the frequency of all arrhythmias was strikingly reduced but their pattern of occurrence remained unchanged. These studies suggest that patients who present with symptoms attributable to arrhythmias tend to have these more frequently during the physical and mental activities of the day and evening presumably due to the accompanying sympathetic overactivity.

[Comparison of the effect of a selective and a nonselective beta receptor blocker on the ischemic ST segment, lung function and stress-induced decrease in blood glucose]

This study was designed to compare the antihypertensive and anti-ischemic effects of the newly developed cardioselective beta-blocking agent, betaxolol, with the non-selective agent, nadolol, both of which have hydrophilic long acting properties, over a period of 48 hours. Additionally, the study was intended to determine whether betaxolol exerts a lesser influence on pulmonary function and whether beta-1- and beta-2-adrenergic blocking agents also induce a decrease in blood glucose levels during standard bicycle ergometry for three to nine minutes, similar to that reported in association with exercise of longer duration and, if so, whether this effect can be circumvented by the use of a selective agent. Ten patients with angiographically documented CAD, stable exercise angina pectoris and reproducible ST-segment depression of at least 1 mm received on day 1, in a single blind fashion, one tablet of placebo, on day 2 and day 7, in a double-blind, randomized and cross-over fashion, 20 mg betaxolol or 80 mg nadolol, respectively. Bicycle ergometry was performed before, four, 24 and 48 hours after drug with fixed work loads, blood glucose determination before and after ergometry four hours after drug and airway resistance and maximal ventilatory capacity studies were carried out five hours after drug administration. As compared with placebo, betaxolol and nadolol led to reductions of ST-segment depression of 65% (p less than 0.01) and 74% (p less than 0.005) at four hours, of 53% (p less than 0.025) and 56% (p less than 0.01) at 24 hours and 41% (p less than 0.05) and 44% (p less than 0.05) at 48 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Temperature and isoproterenol modulation of beta-adrenergic receptor characteristics

Since agonists and temperature affect receptor affinity, and since these factors may influence the actual determination of receptor affinity, we assessed the in vitro effects of temperature and isoproterenol on the high and low affinity states of beta-adrenergic receptors in rat membrane preparations. There was a temperature-dependent decrease in beta-adrenergic receptor agonist affinity which was further promoted by the presence of isoproterenol. The decrease in receptor agonist affinity was reflected by a decrease in the number of receptors in the high affinity state. These data suggest that receptor desensitization may occur in membrane preparations in vitro and that the present methodology used to assess agonist affinity in vitro may itself alter the very properties being measured.

Effects of celiprolol on reflex control of the cardiovascular system in essential hypertension

We have previously shown that baroreceptor control of the cardiovascular system and the cardiopulmonary receptor control of peripheral circulation are preserved or only moderately reduced during antihypertensive treatment with acebutolol or nadolol, which indicates that treatment with beta blockers with or without intrinsic sympathomimetic activity does not impair fundamental neural mechanisms involved in circulatory homeostasis. In the present study we have investigated the reflex control of circulation before and during antihypertensive treatment with celiprolol, which, in addition to its beta-blocking action, has vasodilator properties that may stem from interference with neural cardiovascular control. In six essential hypertensive subjects we measured blood pressure (intraarterial catheter), heart rate (ECG recording), central venous pressure (right atrial catheter), and forearm blood flow and resistance (plethysmography) before and during alterations in the activity of the arterial baroreceptors obtained by means of lower body suction and passive leg raising. The study was performed before and after 5-7 days of oral administration of celiprolol at 200-400 mg once a day. Compared to the values obtained in the control, condition celiprolol caused a reduction in blood pressure, a slight change in heart rate, and an increase in forearm blood flow, which indicated the occurrence of a clear-cut forearm vasodilatation. The heart rate responses to arterial baroreceptor manipulation were unchanged by celiprolol which reset the carotid baroreflex so that its tonic restraint on blood pressure increased despite the hypotension induced by the drug. The inhibitory restraint tonically exerted by the cardiopulmonary receptors on peripheral circulation was also increased by celiprolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Catechol-O-methyltransferase: substrate-specificity and stereoselectivity for beta-adrenoceptor agents

Isoprenaline, isoetharine, rimiterol, dobutamine and nadolol were investigated as substrates for purified pig-liver catechol-O-methyltransferase using a sensitive spectrophotometric assay. Kinetic parameters, Km and Vmax, were defined and the apparent first-order rate constant (Vmax/Km) was derived. On the basis of the apparent first-order rate constant, rimiterol was found to be a 1.5-fold and dobutamine a 5-fold better substrate for catechol-O-methyltransferase than isoprenaline; isoetharine shows no improvement over isoprenaline. Nadolol is not a substrate for catechol-O-methyltransferase. O-Methylation of isoprenaline- and noradrenaline-enantiomers was found to be stereoselective: catechol-O-methyltransferase shows selectivity towards the laevo (-) isomer with respect to the (+) form or racemic mixture. The investigation indicated stereochemical and steric determinants important in the interaction of catechol-O-methyltransferase with physiologically and clinically important beta-adrenoceptor agents.

The antihypertensive effects of doxazosin: a clinical overview

Doxazosin is a long-acting selective alpha 1-adrenoceptor antagonist which has been shown to be effective and well tolerated in the treatment of hypertension given in once-daily doses as monotherapy for up to 1 year or as an adjunct to thiazide or beta-adrenoceptor blockers. Doxazosin has a pharmacokinetic profile in both young adult and elderly subjects which is compatible with once-daily administration. This has been confirmed by measurement of steady state pharmacokinetics in patients receiving long-term doxazosin therapy. In controlled double-blind studies involving approximately 550 patients on doxazosin 1-16 mg once daily, significant reductions in both standing and supine BP were maintained throughout the 24 h dosing interval. Effectiveness of doxazosin in terms of BP lowering and proportion of responders was similar to that achieved with hydrochlorothiazide 25-100 mg once daily, atenolol 50-100 mg once daily, nadolol 40-160 mg once daily, metoprolol 100-200 mg per day given twice daily, or prazosin 1-20 mg per day given twice daily. Doxazosin was as effective in elderly patients as in the younger age group and was as effective in blacks as in caucasians. Doxazosin was well tolerated. Side-effects were generally mild to moderate in severity. Overall incidence, including postural effects early in treatment, was similar to that seen with the comparative agents. In comparison with placebo, doxazosin favourably increased (P less than 0.05) the HDL/total cholesterol ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Desensitization and resensitization of beta-adrenergic receptors in a smooth muscle cell line

Exposure to the beta-adrenergic agonist, metaproterenol, elicits extensive receptor loss and desensitization of adenylate cyclase activity in the hamster DDT1, MF-2 cell line. The reappearance of beta-adrenergic receptors and restoration of adenylate cyclase activity were investigated. Receptor reappearance was investigated under conditions in which lost receptors were not detectable either on the cell surface or within the cell. Exposure to metaproterenol resulted in a 3-5-fold decrease in beta-adrenergic receptor affinity for agonist, an 85% reduction in beta-adrenergic receptor number per cell, and a 65% reduction in isoproterenol-stimulated adenylate cyclase activity without any change in NaF-stimulated enzyme activity. The rate of reappearance of the lost receptors was proportional to the concentration of metaproterenol to which the cells were initially exposed. Metaproterenol, at a concentration of 250 microM, induced long-term receptor loss which required 16 days in fresh media devoid of metaproterenol before the full complement of receptors reappeared. This prolonged receptor loss may be due to residual metaproterenol; however, the resensitization of isoproterenol-stimulated adenylate cyclase activity was restored 2 days after removal of metaproterenol. The lag period for the reappearance of receptors was shortened by incubation with either the beta-adrenergic antagonist, nadalol, or the glucocorticoid, methylprednisolone. Both pharmaceuticals reversed receptor down-regulation and up-regulated receptor number in control cells, although the extent and time course of restoration were different. These data suggest that the process of resensitization in DDT1 cells involves rapid restoration of adenylate cyclase activity and a slower reappearance of receptors over a time period of six population doublings.

The management of severe hypertension with minoxidil in a once-a-day treatment regimen

We evaluated the antihypertensive efficacy of "once-a-day" minoxidil, given in conjunction with a diuretic and sympatholytic, and the effect of this simple regimen on patient compliance. Twenty-one severely hypertensive patients had their existing antihypertensive regimens changed to a single daily dose of chlorthalidone (50-100 mg) and either nadolol (160 mg) or reserpine (.25 mg) for a 3-week period. After stabilization on these two drugs, a single daily dose of minoxidil (2.5 mg) was added to each patient's regimen. Doses were titrated as necessary to achieve diastolic blood pressures of less than 90 mmHg. After 3 and 6 months of maintenance therapy, blood pressures were measured 24 hours after the previous day's dosing to evaluate the persistence of the antihypertensive effect. Twenty-four-hour blood pressure control was achieved on 76% of these occasions, and on at least one occasion in 90% of the patients. In addition, compliance was excellent.

Effect of beta blockade on singing performance

The symptoms associated with performance anxiety, or the so-called stage fright syndrome, are similar to those of alpha and beta adrenergic stimulation. Suppression of symptoms and improvement in instrumentalist's performance after beta blockade suggest that this modality would be of benefit for singers as well. To evaluate the dose-effect relationship of beta blockade upon singing performance and the possible effect of these agents upon performance maturation, we studied 34 singing students during end of semester juries, using a double-blind crossover paradigm. Students performed once with either placebo, 20, 40, or 80 mg of nadolol, and again 48 hours later, with placebo. There was a significant dose-related, limiting effect upon intraperformance cardiac rate. A small, but statistically significant, dichotomous effect upon performance rating was noted: low-dose nadolol tended to enhance performance, whereas larger doses impaired performance. We conclude that the effects of low dose beta blockade upon singing are minimally helpful and high doses may detract from performance ability.

[Use of ion-exchange sorbents for determining drug preparations and their metabolites in biological fluids by high-performance liquid chromatography]

High performance liquid chromatography has acquired great importance recently for an analysis of the drugs in biological fluids of the body. Phase inversion sorbents are particularly widely used today. However, the use of ion-exchange sorbents is fairly promising for an analysis of the drugs capable of ionizing in an aqueous solution. The authors illustrate the use of the latter ones for determination in the blood, urine and saliva of man of a number of the cardiologic drugs (etmozine, nonachlazine, verapamil, prazosin, propranolol, nadolol). Ion-exchange sorbents make it possible to attain better results than inverse phase ones, since they retain the drugs selectively and do not retain the endogenous substances of lipid nature. As regards verapamil, prazosin and propranolol, the unchanged drug and polar metabolites could be determined jointly, with such a determination being not feasible with the use of phase inversion sorbents. Separation of the diastereoisomers of nadolol was achieved in the blood and urine of patients who received the drug.

Myocardial hypertrophy in rats with renal insufficiency

Increased defatted dry wt of the heart and increased heart calcium content were observed in subtotally nephrectomized male Sprague-Dawley rats compared with sham-operated pairfed controls. Increased heart wt contrasted with no change of the weight of viscera (liver, spleen) and markedly decreased weight of striated muscle. Heart wt was unchanged after 5 days of renal insufficiency, but significantly increased after 14 or 21 days. Increased heart wt persisted despite effective beta adrenoreceptor blockade (2 X 10 mg metroprolol/kg/day i.p.) or effective alpha-1-adrenoreceptor blockade (2 X 2 mg prazosin/kg/day i.p.). Increased heart wt was also demonstrable despite normalization of basal blood pressure (intraarterial blood pressure measurement in conscious animals): blood pressure was lowered in one series with hydralazine/nadolol in drinking water (calculated to deliver 20 and 2 mg/kg/day, respectively) and in another series with furosemide in drinking water (15 mg/kg/day) combined with metoprolol (2 X 10 mg/kg/day i.p.). Increased heart wt was also noted despite correction of anemia by blood transfusion (Hct greater than 40%) and after parathyroidectomy in animals kept eucalcemic with high dietary calcium. Micromorphometry of left ventricular myocardium in perfusion-fixed tissue showed no significant change of the relative proportion of connective tissue and myocardial fibers. Myocardial isomyosin pattern was changed with an increase of fast-migrating V1 isomyosin in animals with renal insufficiency compared to sham-operated pairfed controls.

Effects of nadolol and propranolol on renal function in hypertensive patients with moderately impaired renal function

Effects of oral administration of equipotent antihypertensive doses of propranolol and nadolol on renal function were examined in 20 hypertensive patients with moderately impaired renal function. Creatinine clearance increased, and serum beta 2-microglobulin concentrations decreased, when patients were switched from propranolol to nadolol therapy (creatinine clearance = 46.7 +/- 4.9 ml min-1 on propranolol and 52.7 +/- 5.9 on nadolol; beta 2-microglobulin = 6.14 +/- 0.66 mg l-1 on propranolol and 5.62 +/- 0.62 on nadolol). When patients were put back on propranolol, their creatinine clearances (45.9 +/- 5.0 ml min-1) and serum beta 2-microglobulin concentrations (6.51 +/- 0.67 mg l-1) returned to values comparable to those obtained before the change to nadolol was made. Serum beta 2-microglobulin concentrations correlated significantly with creatinine clearance (r = -0.819, P less than 0.001).

Tremor: an alternative approach for investigating adrenergic mechanisms in thyrotoxicosis?

The effects of nadolol (or placebo) and carbimazole on thyrotoxic tremor were investigated in 18 thyrotoxic patients. Both nadolol and carbimazole produced significant reductions in tremor power although nadolol did not cause any change in serum free tri-iodothyronine and free thyroxine concentrations. The results are discussed in terms of the pathogenesis of thyrotoxic tremor and the potential usefulness of tremor in the investigation of adrenergic mechanisms in thyrotoxicosis.

Interactions of beta-adrenoceptor antagonists and thyroid hormones in the control of heart rate in the dog

Propranolol, sotalol and nadolol have been infused into conscious dogs, and doses at which the three drugs are equipotent as beta-adrenoceptor antagonists determined. In euthyroid dogs, sotalol was more effective at lowering heart-rate than an equivalent dose of propranolol, while an equivalent dose of nadolol was without effect. Hyperthyroidism potentiated the lowering of heart-rate by sotalol, but inhibited that by propranolol. The effect of sotalol on heart-rate was correlated with its prolongation of the Q-T interval of the ECG. That of propranolol was correlated with its prolongation of the P-R interval. Nadolol did not affect P-R interval or Q-T interval except at relatively high dosage. We conclude that the tachycardia of hyperthyroidism is not affected by blockade of beta-adrenoceptors and therefore that it is not mediated by adrenergic mechanisms. The effectiveness of propranolol and sotalol in lowering heart-rate must be due to actions peculiar to those drugs, and not to beta-adrenoceptor antagonism.

The effect of a once-daily oral dose of nadolol on intraocular pressure in normal volunteers

We compared the effects of once-daily oral administration of 20 mg and 40 mg of nadolol vs placebo in 40 normal volunteers in a randomized, double-masked trial. Each of 23 women and 17 men (ranging in age from 18 to 50 years) had intraocular pressure, pulse rate, blood pressure, pupil size, amplitude of accommodation, and near point measured immediately before treatment and then at 24 hours, day 8, and day 15 after treatment. Both dosages of nadolol produced significant decreases in intraocular pressure at three hours (P less than .001). Although both dosages decreased intraocular pressure at 24 hours compared with placebo, only the change with the 40-mg dose was significant (P less than .05). Although both dosages produced significant decreases in pulse rate and blood pressure, side effects were minimal.

The clinical and metabolic responses to early surgical treatment for hyperthyroid Graves' disease: a comparison of three pre-operative treatment regimens

We have compared the clinical and metabolic responses of three groups of patients undergoing subtotal thyroidectomy for hyperthyroid Graves' disease. These patients were prepared for surgery with propranolol alone, propranolol plus potassium iodide or the long acting beta-adrenoceptor antagonist nadolol plus potassium iodide. Pre-treatment with potassium iodide reduced serum T4 to normal or subnormal in all patients. Patients in the propranolol group had significantly higher pulse rates and temperatures after operation and one patient developed an exacerbation of the hypermetabolic state. The perioperative rise in serum cortisol and blood glucose was delayed in patients in the propranolol group and this was also noted in one severely hyperthyroid patient on propranolol + potassium iodide. Nadolol was administered once daily as compared to multiple daily doses with propranolol. Despite this, plasma nadolol levels were consistently higher throughout the perioperative period while propranolol levels in patients on both propranolol alone and propranolol + potassium iodide were highly variable and sometimes undetectable. We conclude that, in the rapid preparation of patients with hyperthyroid Graves' disease for surgery, the combination of nadolol + potassium iodide has significant advantages over the other two regimens.

Neonatal effects of maternal nadolol therapy

Described is the case of an infant, exposed during gestation to the beta-blocker nadolol, who experienced cardiorespiratory depression, mild hypoglycemia, and growth retardation. The longer duration of action of nadolol and the fact that it is only 30% protein bound make it less desirable than propranolol for use as a beta-blocker during pregnancy.