Power spectrum analysis of heart rate fluctuations provides a quantitative noninvasive means of assessing the functioning of the short-term cardiovascular control systems. We show that sympathetic and parasympathetic nervous activity make frequency-specific contributions to the heart rate power spectrum, and that renin-angiotensin system activity strongly modulates the amplitude of the spectral peak located at 0.04 hertz. Our data therefore provide evidence that the renin-angiotensin system plays a significant role in short-term cardiovascular control in the time scale of seconds to minutes.
Aortic aneurysm and dissection are manifestations of Marfan syndrome (MFS), a disorder caused by mutations in the gene that encodes fibrillin-1. Selected manifestations of MFS reflect excessive signaling by the transforming growth factor-beta (TGF-beta) family of cytokines. We show that aortic aneurysm in a mouse model of MFS is associated with increased TGF-beta signaling and can be prevented by TGF-beta antagonists such as TGF-beta-neutralizing antibody or the angiotensin II type 1 receptor (AT1) blocker, losartan. AT1 antagonism also partially reversed noncardiovascular manifestations of MFS, including impaired alveolar septation. These data suggest that losartan, a drug already in clinical use for hypertension, merits investigation as a therapeutic strategy for patients with MFS and has the potential to prevent the major life-threatening manifestation of this disorder.
Spectral analysis of spontaneous heart rate fluctuations were assessed by use of autonomic blocking agents and changes in posture. Low-frequency fluctuations (below 0.12 Hz) in the supine position are mediated entirely by the parasympathetic nervous system. On standing, the low-frequency fluctuations increase and are jointly mediated by the sympathetic and parasympathetic nervous systems. High-frequency fluctuations, at the respiratory frequency, are decreased by standing and are mediated solely by the parasympathetic system. Heart rate spectral analysis is a powerful noninvasive tool for quantifying autonomic nervous system activity.
We conducted a multicenter randomized double-blind clinical trial among 626 men with mild to moderate hypertension to determine the effects of captopril, methyldopa, and propranolol on their quality of life. Hydrochlorothiazide was added if needed to control blood pressure. After a 24-week treatment period, all three groups had similar blood-pressure control, although fewer patients taking propranolol required hydrochlorothiazide. Patients taking captopril alone or in combination with a diuretic were least likely to withdraw from treatment because of adverse effects (8 percent vs. 20 percent for methyldopa and 13 percent for propranolol). The treatment groups were similar in scores for sleep dysfunction, visual memory, and social participation. However, patients taking captopril, as compared with patients taking methyldopa, scored significantly higher (P less than 0.05 to less than 0.01) on measures of general well-being, had fewer side effects, and had better scores for work performance, visual-motor functioning, and measures of life satisfaction. Patients taking propranolol also reported better work performance than patients taking methyldopa. Patients taking captopril reported fewer side effects and less sexual dysfunction than those taking propranolol and had greater improvement (P less than 0.05 to less than 0.01) on measures of general well-being. Our findings show that antihypertensive agents have different effects on the quality of life and that these can be meaningfully assessed with available psychosocial measures.
The main aim of the trial was to determine whether drug treatment of mild hypertension (phase V diastolic pressure 90-109 mm Hg) reduced the rates of stroke, of death due to hypertension, and of coronary events in men and women aged 35-64 years. Subsidiary aims were: to compare the course of blood pressure in two groups, one taking bendrofluazide and one taking propranolol, and to compare the incidence of suspected adverse reactions to these two drugs. The study was single blind and based almost entirely in general practices; 17 354 patients were recruited, and 85 572 patient years of observation have accrued. Patients were randomly allocated at entry to take bendrofluazide or propranolol or placebo tablets. The primary results were as follows. The stroke rate was reduced on active treatment: 60 strokes occurred in the treated group and 109 in the placebo group, giving rates of 1.4 and 2.6 per 1000 patient years of observation respectively (p less than 0.01 on sequential analysis). Treatment made no difference, however, to the overall rates of coronary events: 222 events occurred on active treatment and 234 in the placebo group (5.2 and 5.5 per 1000 patient years respectively). The incidence of all cardiovascular events was reduced on active treatment: 286 events occurred in the treated group and 352 in the placebo group, giving rates of 6.7 and 8.2 per 1000 patient years respectively (p less than 0.05 on sequential analysis). For mortality from all causes treatment made no difference to the rates. There were 248 deaths in the treated group and 253 in the placebo group (rates 5.8 and 5.9 per 1000 patient years respectively). Several post hoc analyses of subgroup results were also performed but they require very cautious interpretation. The all cause mortality was reduced in men on active treatment (157 deaths versus 181 in the placebo group; 7.1 and 8.2 per 1000 patient years respectively) but increased in women on active treatment (91 deaths versus 72; 4.4 and 3.5 per 1000 patient years respectively). The difference between the sexes in their response to treatment was significant (p = 0.05). Comparison of the two active drugs showed that the reduction in stroke rate on bendrofluazide was greater than that on propranolol (p = 0.002). The stroke rate was reduced in both smokers and non-smokers taking bendrofluazide but only in non-smokers taking propranolol. This difference between the responses to the two drugs was significant (p = 0.03).(ABSTRACT TRUNCATED AT 400 WORDS)
Ventricular arrhythmias and contractile dysfunction are the main causes of death in human heart failure (HF). In a rabbit HF model reproducing these same aspects of human HF, we demonstrate that a 2-fold functional upregulation of Na(+)-Ca(2+) exchange (NaCaX) unloads sarcoplasmic reticulum (SR) Ca(2+) stores, reducing Ca(2+) transients and contractile function. Whereas beta-adrenergic receptors (beta-ARs) are progressively downregulated in HF, residual beta-AR responsiveness at this critical HF stage allows SR Ca(2+) load to increase, causing spontaneous SR Ca(2+) release and transient inward current carried by NaCaX. A given Ca(2+) release produces greater arrhythmogenic inward current in HF (as a result of NaCaX upregulation), and approximately 50% less Ca(2+) release is required to trigger an action potential in HF. The inward rectifier potassium current (I(K1)) is reduced by 49% in HF, and this allows greater depolarization for a given NaCaX current. Partially blocking I(K1) in control cells with barium mimics the greater depolarization for a given current injection seen in HF. Thus, we present data to support a novel paradigm in which changes in NaCaX and I(K1), and residual beta-AR responsiveness, conspire to greatly increase the propensity for triggered arrhythmias in HF. In addition, NaCaX upregulation appears to be a critical link between contractile dysfunction and arrhythmogenesis.
Substantial evidence from animal studies suggests that enhanced memory associated with emotional arousal results from an activation of beta-adrenergic stress hormone systems during and after an emotional experience. To examine this implication in human subjects, we investigated the effect of the beta-adrenergic receptor antagonist propranolol hydrochloride on long-term memory for an emotionally arousing short story, or a closely matched but more emotionally neutral story. We report here that propranolol significantly impaired memory of the emotionally arousing story but did not affect memory of the emotionally neutral story. The impairing effect of propranolol on memory of the emotional story was not due either to reduced emotional responsiveness or to nonspecific sedative or attentional effects. The results support the hypothesis that enhanced memory associated with emotional experiences involves activation of the beta-adrenergic system.
Infections are a leading cause of death in stroke patients. In a mouse model of focal cerebral ischemia, we tested the hypothesis that a stroke-induced immunodeficiency increases the susceptibility to bacterial infections. 3 d after ischemia, all animals developed spontaneous septicemia and pneumonia. Stroke induced an extensive apoptotic loss of lymphocytes and a shift from T helper cell (Th)1 to Th2 cytokine production. Adoptive transfer of T and natural killer cells from wild-type mice, but not from interferon (IFN)-gamma-deficient mice, or administration of IFN-gamma at day 1 after stroke greatly decreased the bacterial burden. Importantly, the defective IFN-gamma response and the occurrence of bacterial infections were prevented by blocking the sympathetic nervous system but not the hypothalamo-pituitary-adrenal axis. Furthermore, administration of the beta-adrenoreceptor blocker propranolol drastically reduced mortality after stroke. These data suggest that a catecholamine-mediated defect in early lymphocyte activation is the key factor in the impaired antibacterial immune response after stroke.
Atrial fibrillation (AF) can be initiated by ectopic beats originating from the atrial or great venous tissues. This study investigated the anatomic characteristics and electrophysiological properties of pulmonary veins (PVs), as well as the possible mechanisms and response to drugs of ectopic foci, and assessed the effects of radiofrequency (RF) ablation on AF initiated by ectopic beats originating from PVs.
Seventy-nine patients with frequent episodes of paroxysmal AF and 10 control patients were included. Distal PVs showed the shortest effective refractory periods (ERPs), and right superior PVs showed a higher incidence of intra-PV conduction block than left superior PVs. Superior and left PVs had longer myocardial sleeves than inferior and right PVs, respectively. These electrophysiological characteristics were similar between AF and control patients. Propranolol, verapamil, and procainamide suppressed ectopic beats that originated from the PVs. Of 116 ectopic foci that initiated AF, 103 (88.8%) originated from PVs. A mean of 7+/-3 RF applications completely eliminated 110 ectopic foci (94.8%). During the 6+/-2-month follow-up period, 68 patients (86. 1%) were free of AF without any antiarrhythmic drugs. Follow-up transesophageal echocardiogram showed 42.4% of ablated PVs had focal stenosis. One patient had mild exertional dyspnea after ablation, but it resolved 3 months later; 1 patient had onset of mild exertional dyspnea 5 months after ablation.
Electrophysiological characteristics of PVs are different from those in the atria. Ectopic beats from PVs can initiate AF, and beta-adrenergic receptor blocker, calcium channel blockers, and sodium channel blockers can suppress these ectopic beats. Careful mapping and elimination of these ectopic foci can cure paroxysmal AF.
Animal studies have shown that fear memories can change when recalled, a process referred to as reconsolidation. We found that oral administration of the beta-adrenergic receptor antagonist propranolol before memory reactivation in humans erased the behavioral expression of the fear memory 24 h later and prevented the return of fear. Disrupting the reconsolidation of fear memory opens up new avenues for providing a long-term cure for patients with emotional disorders.
The beta-Blocker Heart Attack Trial (BHAT) was a National Heart, Lung, and Blood Institute-sponsored, multicenter, randomized, double-blind, and placebo-controlled trial designed to test whether the regular administration of propranolol hydrochloride to men and women who had experienced at least one myocardial infarction would result in a significant reduction in total mortality during a two- to four-year period. During a 27-month interval, 3,837 persons between the ages of 30 and 69 years were randomized to either propranolol (1,916 persons) or placebo (1,912 persons), five to 21 days after the infarction. Depending on serum drug levels, the prescribed maintenance dose of propranolol hydrochloride was either 180 or 240 mg/day. The trial was stopped nine months ahead of schedule. Total mortality during the average 24-month follow-up period was 7.2% in the propranolol group and 9.8% in the placebo group. Arteriosclerotic heart disease (ASHD) mortality was 6.2% in the propranolol group and 8.5% in the placebo group. Sudden cardiac death, a subset of ASHD mortality, was 3.3% among the propranolol patients and 4.6% among the placebo patients. Serious side effects were uncommon. Hypotension, gastrointestinal problems, tiredness, bronchospasm, and cold hands and feet occurred more frequently in the propranolol group. Based on the BHAT results, the use of propranolol in patients with no contraindications to beta-blockade who have had a recent myocardial infarction is recommended for at least three years.
Consolidation is a process through which labile memories are made persistent [Science 287 (2000) 248]; [Annu Rev Psychol 55 (2004) 51]. When retrieved, a consolidated memory is rendered labile again and undergoes reconsolidation [Learn Mem 7 (2000) 73]; [Trends Neurosci 26 (2003) 65]). Reconsolidation thus offers the opportunity to manipulate memory after it is formed, and may therefore provide a means of treating intrusive memories associated with post-traumatic stress disorder (PTSD). Reconsolidation is most usually studied using protein synthesis inhibitors, which is not practical in humans. However, the beta adrenergic receptor antagonist propranolol impairs consolidation of declarative memory in humans [Science 287 (2000) 248]; [Nature 371 (1994) 702] and consolidation and reconsolidation of inhibitory avoidance learning in rats [Brain Res 368 (1986) 125]; [J Neurosci 19 (1999) 6623]. Here, we show that systemic or intra-amygdala infused propranolol blocks reconsolidation but not consolidation. If the effects on reconsolidation are verified in humans, the results would suggest the possibility that propranolol after memory retrieval might be an effective way of treatment of intrusive memories in PTSD. That the systemic effects of propranolol on reconsolidation are achieved via an action in the amygdala is especially important in light of the fact that PTSD involves alterations in the amygdala [Arch Gen Psychiatry 53 (1996) 380].
We investigated the hypothesis that beat-to-beat variability in hemodynamic parameters reflects the dynamic interplay between ongoing perturbations to circulatory function and the compensatory response of short-term cardiovascular control systems. Spontaneous fluctuations in heart rate (HR), arterial blood pressure, and respiration were analyzed by spectral analysis in the 0.02- to 1-Hz frequency range. A simple closed-loop model of short-term cardiovascular control was proposed and evaluated in a series of experiments: pharmacological blockades of the parasympathetic, alpha-sympathetic, beta-sympathetic, and renin-angiotensin systems were used to open the principal control loops in order to examine changes in the spectral pattern of the fluctuations. Atrial pacing was used to examine blood pressure variability in the absence of HR variability. We found that respiratory frequency fluctuations in HR are parasympathetically mediated and that blood pressure fluctuations at this frequency result almost entirely from the direct effect of centrally mediated HR fluctuations. The sympathetic nervous system appears to be too sluggish to mediate respiratory frequency variations. Low-frequency (0.02-0.09 Hz) fluctuations in HR are jointly mediated by the parasympathetic and beta-sympathetic systems and appear to compensate for blood pressure fluctuations at this frequency. Low-frequency blood pressure fluctuations are probably due to variability in vasomotor activity which is normally damped by renin-angiotensin system activity. Blockade of the alpha-adrenergic system, however, does not significantly alter low-frequency blood pressure fluctuations.
Preclinical considerations suggest that treatment with a beta-adrenergic blocker following an acute psychologically traumatic event may reduce subsequent posttraumatic stress disorder (PTSD) symptoms. This pilot study addressed this hypothesis.
Patients were randomized to begin, within 6 hours of the event, a 10-day course of double-blind propranolol (n = 18) versus placebo (n = 23) 40 mg four times daily.
The mean (SD) 1-month Clinician-Administered PTSD Scale (CAPS) score of 11 propranolol completers was 27.6 (15.7), with one outlier 5.2 SDs above the others' mean, and of 20 placebo completers, 35.5 (21.5), t = 1.1, df = 29, p =.15. Two propranolol patients' scores fell above, and nine below, the placebo group's median, p =.03 (sign test). Zero of eight propranolol, but six of 14 placebo, patients were physiologic responders during script-driven imagery of the traumatic event when tested 3 months afterward, p =.04 (all p values one-tailed).
These pilot results suggest that acute, posttrauma propranolol may have a preventive effect on subsequent PTSD.
The structural relationships between interstitial cells of Cajal (ICC), varicose nerve fibers, and smooth muscle cells in the gastrointestinal tract have led to the suggestion that ICC may be involved in or mediate enteric neurotransmission. We characterized the distribution of ICC in the murine stomach and found two distinct classes on the basis of morphology and immunoreactivity to antibodies against c-Kit receptors. ICC with multiple processes formed a network in the myenteric plexus region from corpus to pylorus. Spindle-shaped ICC were found within the circular and longitudinal muscle layers (IC-IM) throughout the stomach. The density of these cells was greatest in the proximal stomach. IC-IM ran along nerve fibers and were closely associated with nerve terminals and adjacent smooth muscle cells. IC-IM failed to develop in mice with mutations in c-kit. Therefore, we used W/W(V) mutants to test whether IC-IM mediate neural inputs in muscles of the gastric fundus. The distribution of inhibitory nerves in the stomachs of c-kit mutants was normal, but NO-dependent inhibitory neuro-regulation was greatly reduced. Smooth muscle tissues of W/W(V) mutants relaxed in response to exogenous sodium nitroprusside, but the membrane potential effects of sodium nitroprusside were attenuated. These data suggest that IC-IM play a critical serial role in NO-dependent neurotransmission: the cellular mechanism(s) responsible for transducing NO into electrical responses may be expressed in IC-IM. Loss of these cells causes loss of electrical responsiveness and greatly reduces responses to nitrergic nerve stimulation.
Treatment of turkey erthrocyte membranes with cholera toxin caused an enhancement of the basal and catecholamine-stimulated adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 184.108.40.206] activities. Both of these activities required the presence of GTP. The toxin effect on the adenylate cyclase activity concided with an inhibition of the catecholamine-stimulated guanosinetriphosphatase activity. Inhibition of the guanosinetriphosphatase, as well as enhancement of the adenylate cyclase activity, showed the same dependence on cholera toxin concentrations, and the effect of the toxin on both activities was dependent on the presence of NAD. It is proposed that continuous GTP hydrolysis at the regulatory guanyl nucleotide site is an essential turn-off mechanism, terminating activation of the adenylate cyclase. Cholera toxin inhibits the turn-off guanosinetriphosphatase reaction and thereby causes activation of the adenylate cyclase. According to this mechanism GTP should activate the toxin-treated preparation of adenylate cyclase, as does the hydrolysis-resistant analog guanosine 5'-(beta,gamma-immino)triphosphate [Gpp(NH)p]. Indeed, the toxin-treated adenylate cyclase was maximally activated, in the presence of isoproternol, by either GTP or Gpp(NH)p, while adenylate cyclase not treated with toxin was stimulated by hormone plus GTP to only one-fifth of the activity achieved with hormone plus Gpp(NH)p. Furthermore, the toxin-treated adenylate cyclase activated by isoproterenol plus GTP remained active for and extended period (half-time of 3 min) upon subsequent addition of the beta-adrenergic blocker, propranolol. The native enzyme, however, was refractory to propranolol only if activated by Gpp(NH)p but not by GTP.
Cessation of drug use in chronic opiate abusers produces a severe withdrawal syndrome that is highly aversive, and avoidance of withdrawal or associated stimuli is a major factor contributing to opiate abuse. Increased noradrenaline in the brain has long been implicated in opiate withdrawal, but it has not been clear which noradrenergic systems are involved. Here we show that microinjection of beta-noradrenergic-receptor antagonists, or of an alpha2-receptor agonist, into the bed nucleus of the stria terminalis (BNST) in rats markedly attenuates opiate-withdrawal-induced conditioned place aversion. Immunohistochemical studies revealed that numerous BNST-projecting cells in the A1 and A2 noradrenergic cell groups of the caudal medulla were activated during withdrawal. Lesion of these ascending medullary projections also greatly reduced opiate-withdrawal-induced place aversion, whereas lesion of locus coeruleus noradrenergic projections had no effect on opiate-withdrawal behaviour. We conclude that noradrenergic inputs to the BNST from the caudal medulla are critically involved in the aversiveness of opiate withdrawal.