Regulation of human leukocyte beta receptors by endogenous catecholamines: relationship of leukocyte beta receptor density to the cardiac sensitivity to isoproterenol

Neutrophil extracellular traps formation may be involved in the association of propranolol with the development of portal vein thrombosis

BACKGROUND & AIMS

Nonselective β blockers (NSBBs) facilitate the development of portal vein thrombosis (PVT) in liver cirrhosis. Considering the potential effect of NSBBs on neutrophils and neutrophil extracellular traps (NETs), we speculated that NSBBs might promote the development of PVT by stimulating neutrophils to release NETs.

MATERIALS AND METHODS

Serum NETs biomarkers were measured, use of NSBBs was recorded, and PVT was evaluated in cirrhotic patients. Carbon tetrachloride and ferric chloride (FeCl3) were used to induce liver fibrosis and PVT in mice, respectively. After treatment with propranolol and DNase I, neutrophils in peripheral blood, colocalization and expression of NETs in PVT specimens, and NETs biomarkers in serum were measured. Ex vivo clots lysis analysis was performed and portal vein velocity and coagulation parameters were tested.

RESULTS

Serum MPO-DNA level was significantly higher in cirrhotic patients treated with NSBBs, and serum H3Cit and MPO-DNA levels were significantly higher in those with PVT. In fibrotic mice, following treatment with propranolol, DNase I significantly shortened the time of FeCl3-induced PVT formation, lowered the peripheral blood neutrophils labelled by CD11b/Ly6G, inhibited the positive staining of H3Cit and the expression of H3Cit and MPO proteins in PVT tissues, and reduced serum nucleosome level. Furthermore, the addition of DNase I to tissue plasminogen activator (tPA) significantly accelerated clots lysis as compared with tPA alone. Propranolol reduced portal vein velocity in fibrotic mice, but did not influence coagulation parameters.

CONCLUSION

Our study provides a clue to the potential impact of NETs formation on the association of NSBBs with the development of PVT.

Interactions between beta-2 adrenoceptor gene variation, cardiovascular control and dietary sodium in healthy young adults

Dietary sodium affects function of the beta-2 adrenoceptor (ADRB2). We tested the hypothesis that haplotype variation in the ADRB2 gene would influence the cardiovascular and regional vasodilator responses to sympathoexcitatory manoeuvres following low, normal and high sodium diets, and ADRB2-mediated forearm vasodilation in the high sodium condition. Seventy-one healthy young adults were grouped by double homozygous haplotypes: Arg16+Gln27 (n = 31), the rare Gly16+Gln27 (n = 10) and Gly16+Glu27 (n = 30). Using a randomized cross-over design, subjects were studied following 5 days of controlled low, normal and high sodium with 1 month or longer between diets (and low hormone phase of the menstrual cycle). All three visits utilized ECG and finger plethysmography for haemodynamic measures, and the high sodium visit included a brachial arterial catheter for forearm vasodilator responses to isoprenaline with plethysmography. Lymphocytes were sampled for ex vivo analysis of ADRB2 density and binding conformation. We found a main effect of haplotype on ADRB2 density (P = 0.03) with the Gly16+Glu27 haplotype having the greatest density (low, normal, high sodium: 12.9 ± 0.9, 13.5 ± 0.9 and 13.6 ± 0.8 fmol mg(-1) protein, respectively) and Arg16+Gln27 having the least (9.3 ± 0.6, 10.1 ± 0.5 and 10.3 ± 0.6  fmol mg(-1) protein, respectively), but there were no sodium or haplotype effects on receptor binding conformation. In the mental stress trial, there was a main effect of haplotype on cardiac output (P = 0.04), as Arg16+Gln27 had the lowest responses. Handgrip and forearm vasodilation yielded no haplotype differences, and no correlations were present for ADRB2 density and haemodynamics. Our findings support cell-based evidence that ADRB2 haplotype influences ADRB2 protein expression independent of dietary sodium, yet the haemodynamic consequences appear modest in healthy humans.

Short-term erythropoietin treatment does not substantially modulate monocyte transcriptomes of patients with combined heart and renal failure

BACKGROUND

Combined heart and renal failure is associated with high cardiovascular morbidity and mortality. Anti-oxidant and anti-inflammatory, non-hematopoietic effects of erythropoietin (EPO) treatment have been proposed. Monocytes may act as biosensors of the systemic environment. We hypothesized that monocyte transcriptomes of patients with cardiorenal syndrome (CRS) reflect the pathophysiology of the CRS and respond to short-term EPO treatment at a recommended dose for treatment of renal anemia.

METHODS

Patients with CRS and anemia (n = 18) included in the EPOCARES trial were matched to healthy controls (n = 12). Patients were randomized to receive 50 IU/kg/week EPO or not. RNA from CD14(+)-monocytes was subjected to genome wide expression analysis (Illumina) at baseline and 18 days (3 EPO injections) after enrolment. Transcriptomes from patients were compared to healthy controls and effect of EPO treatment was evaluated within patients.

RESULTS

In CRS patients, expression of 471 genes, including inflammation and oxidative stress related genes was different from healthy controls. Cluster analysis did not separate patients from healthy controls. The 6 patients with the highest hsCRP levels had more differentially expressed genes than the 6 patients with the lowest hsCRP levels. Analysis of the variation in log(2) ratios of all individual 18 patients indicated that 4 of the 18 patients were different from the controls, whereas the other 14 were quite similar. After short-term EPO treatment, every patient clustered to his or her own baseline transcriptome. Two week EPO administration only marginally affected expression profiles on average, however, individual gene responses were variable.

CONCLUSIONS

In stable, treated CRS patients with mild anemia, monocyte transcriptomes were modestly altered, and indicated imprints of inflammation and oxidative stress. EPO treatment with a fixed dose has hematopoietic effects, had no appreciable beneficial actions on monocyte transcription profiles, however, could also not be associated with undesirable transcriptional responses.

Basics and dynamics of neonatal and pediatric pharmacology

Understanding the role of ontogeny in the disposition and actions of medicines is the most fundamental prerequisite for safe and effective pharmacotherapeutics in the pediatric population. The maturational process represents a continuum of growth, differentiation, and development, which extends from the very small preterm newborn infant through childhood, adolescence, and to young adulthood. Developmental changes in physiology and, consequently, in pharmacology influence the efficacy, toxicity, and dosing regimen of medicines. Relevant periods of development are characterized by changes in body composition and proportion, developmental changes of physiology with pathophysiology, exposure to unique safety hazards, changes in drug disposition by major organs of metabolism and elimination, ontogeny of drug targets (e.g., enzymes, transporters, receptors, and channels), and environmental influences. These developmental components that result in critical windows of development of immature organ systems that may lead to permanent effects later in life interact in a complex, nonlinear fashion. The ontogeny of these physiologic processes provides the key to understanding the added dimension of development that defines the essential differences between children and adults. A basic understanding of the developmental dynamics in pediatric pharmacology is also essential to delineating the future directions and priority areas of pediatric drug research and development.

Adrenergic receptors. Methods of determination and mechanisms of regulation

The radioligand binding technique has been proven useful in the study of altered responsiveness after exposure to adrenergic agents. A reduction in receptor number has generally been reported after interventions serving to increase the stimulatory input to the receptors prior to assay. Conversely a decrease in receptor stimulation has been demonstrated to induce an elevation in receptor density. These phenomena have been described for alpha- as well as for beta-adrenoceptors in various tissues under a variety of experimental conditions such as prolonged agonist exposure, chronic receptor blockade, denervation and interference with catecholamine turnover. A number of clinically relevant cardiovascular experimental models have been characterized by altered adrenoceptor densities, possibly reflecting a compensatory resetting of sympathetic tone in response to an aberrant haemodynamic pattern. The mechanisms underlying receptor density changes as those discussed have been suggested to involve an internalization process which may involve phospholipase and transglutaminase activation in the cell membrane.

Long-term beta 1-selective adrenergic blockade and adrenergic receptors in human subcutaneous adipocytes

The influence of beta-adrenergic blockade with metoprolol, a beta 1-selective agent, on the adrenergic regulation of lipid mobilization was explored in subcutaneous adipocytes removed from 13 patients with essential hypertension. Treatment with metoprolol, which was associated with adequate beta-adrenergic blockade and an antihypertensive effect, resulted in a significant increase (p less than 0.05) in the binding of the beta-adrenergic antagonist (-)-(3H)-dihydroalprenolol and a 50% increase (p less than 0.01) in the maximum lipolytic response to the beta-adrenergic agonist isopropylnoradrenaline. In 7 patients with normotriglyceridaemia the total plasma triglyceride level increased significantly (p less than 0.025) during metoprolol treatment, a change that was due to an increase in the very low density lipoprotein triglycerides. The findings suggest that chronic treatment with the beta 1-selective adrenergic blocker metoprolol leads to a significant increase in beta-adrenoceptor density and an increase in the lipolytic response to beta-adrenergic agonists. This latter finding may, in some measure, account for the increased plasma triglyceride level observed.

A 5-year longitudinal study of the relationships between stress, coping, and immune cell beta(2)-adrenergic receptor sensitivity

Caring for a spouse with Alzheimer's disease (AD) is associated with overall health decline and impaired cardiovascular functioning. This morbidity may be related to the effects of caregiving stress and impaired coping on beta(2)-adrenergic receptors, which mediate hemodynamic and vascular responses and are important for peripheral blood mononuclear cell (PBMC) trafficking and cytokine production. This study investigated the longitudinal relationship between stress, personal mastery, and beta(2)-adrenergic receptor sensitivity assessed in vitro on PBMC. Over a 5-year study, 115 spousal AD caregivers completed annual assessments of caregiving stress, mastery, and PBMC beta(2)-adrenergic receptor sensitivity, as assessed by in vitro isoproterenol stimulation. Heightened caregiving stress was associated with significantly decreased receptor sensitivity, whereas greater sense of personal mastery was associated with significantly increased receptor sensitivity. These results suggest that increased stress may be associated with a desensitization of beta(2)-receptors, which may contribute to the development of illness among caregivers. However, increased mastery is associated with increased receptor sensitivity, and may therefore serve as a resource factor for improved health in this population.

Effect of weightlifting upon left ventricular function and markers of cardiomyocyte damage

The purpose of this study was to assess left ventricular (LV) function and biochemical markers of myocyte after prolonged weightlifting activity. Seventeen male subjects (age range 20-34 years) performed a 90-min bout of weightlifting exercise consisting of three sets of 8-10 repetitions at 70% one-repetition maximum. Body mass, heart rate, systolic blood pressure (SBP) and echocardiographically determined indices of LV loading (LV internal diameter during diastole, LV meridonial wall stress), systolic function (stroke volume (SV), ejection fraction (EF), end-systolic pressure volume relationship; SBP/ESV) and diastolic filling (ratio of early to late; E:A) were obtained pre-exercise, immediately after and 24 h post-exercise. A 5-ml venous blood sample was obtained for the assessment of cardiac troponin T (cTnT) via third generation electrochemiluminescence assay. Data were assessed via one-way ANOVA and Pearson's correlation. Although SV declined (80.9 +/- 18.3 vs. 66.9 +/- 17.2, p < 0.05) there was no alteration in LV contractility (EF 62 +/- 6 vs. 59 +/- 7; SBP/ESV 3.51 +/- 1.4 vs. 3.51 +/- 1.4, p > 0.05). The E:A ratio was significantly decreased following exercise (1.78 +/- 0.41 vs. 1.33 +/- 0.37, p < 0.05). This decrease was not fully explained by loading conditions (r2 = 0.05 to 0.24). All values returned to baseline 24 h post-exercise. No cTnT was reported in any of the blood samples. In conclusion, there was no significant evidence of any LV contractile depression and no cTnT was observed post exercise. The small reduction in diastolic filling could not be explained by changes in haemodynamic loading or the post-exercise elevation in heart rate.

Increased beta-adrenergic sensitivity correlates with visceral hypersensitivity in patients with constipation-predominant irritable bowel syndrome

Autonomic imbalance has been proposed to be a pathophysiological factor for irritable bowel syndrome (IBS). The aim of this study was to assess beta-adrenergic abnormalities in IBS and to evaluate their relationship to visceral hypersensitivity and other symptoms of IBS patients. Sixteen IBS patients and 16 control subjects were recruited into this study. Participants were asked to complete a questionnaire regarding bowel symptoms, and in order to study beta-adrenergic sensitivity, isoproterenol stimulation tests were performed and visceral hypersensitivity was evaluated by barostat test. Results showed that beta-adrenergic activity and rectal sensitivity were more pronounced in IBS patients than in normal control patients (P < 0.01). Although both IBS subgroups also exhibited more pronounced beta-adrenergic sensitivity than did the controls (P < 0.05), a significant correlation between beta-adrenergic activity and maximally tolerable pressures on the barostat test was found only in IBS-C patients (P = 0.03, R = 0.855). In addition, patients with "hard or lumpy" stools exhibited a higher degree of beta-adrenergic activity (P = 0.00). We conclude that increased beta-adrenergic activity significantly correlated with visceral hypersensitivity in constipation-predominant IBS and symptoms of hard or lumpy stools in IBS patients.

??-Adrenoceptor-mediated, nitric-oxide-dependent vasodilatation is abnormal in early hypertension

BACKGROUND

It is unknown whether beta-adrenoceptor-mediated vasodilatation is altered in early hypertension and whether it can be modulated by L-arginine.

METHODS AND DESIGN

We measured changes in forearm blood flow by plethysmography in response to acetylcholine (9 and 37 microg/min), sodium nitroprusside (200 and 800 ng/min) and the beta-receptor agonist, isoproterenol (50 and 200 ng/min) in 12 patients with essential hypertension (group EH) and in healthy volunteers with (group PFH; n = 14) and without (group NFH; n = 14) a family history of essential hypertension, before and during concomitant infusion of L-arginine (10 micromol/min). In five individuals from each group, infusion of acetylcholine and isoproterenol was repeated during the concurrent blockade of nitric oxide synthesis by N-monomethyl-L-arginine (L-NMMA; 4 micromol/min).

RESULTS

The response to acetylcholine was reduced in groups EH and PFH compared with group NFH (both P < 0.05), whereas the vasodilator effects of isoproterenol and sodium nitroprusside were similar in all three groups. Acetylcholine- and isoproterenol-induced vasodilatation did not change during infusion of the nitric oxide precursor, L-arginine, in group NFH, but were significantly enhanced by L-arginine in groups PFH and EH [forearm blood flow before and after isoproterenol 200 ng/min: group PFH 11.8 +/- 1.02 and 13.3 +/- 1.08 ml/min, respectively (P < 0.05); group EH: 11.3 +/- 1.57 and 14.9 +/- 1.91 ml/min, respectively (P < 0.01)]. Co-infusion of L-NMMA blunted the response to acetylcholine and isoproterenol in group NFH (P < 0.05), but did not significantly modify vasodilatation in groups PFH and EH.

CONCLUSIONS

Although beta-adrenergic vasodilatation seemed to be unaltered in early hypertension, L-arginine enhanced the response to isoproterenol, whereas concomitant inhibition of nitric oxide synthase by L-NMMA had no significant effect. These findings suggest that the nitric oxide component of isoproterenol-mediated vasodilatation is impaired in early hypertension and possibly compensated by increased beta-adrenoceptor responsiveness of smooth muscle cells. In this setting, supplementation of the nitric oxide precursor, L-arginine, enhances the vasodilator response to beta-adrenergic stimulation.

Catecholamine-induced Regulation in Vitro and ex Vivo of Intralymphocyte Ionized Magnesium

Despite the importance of the adrenergic activity and of the metabolism of magnesium in some important cardiovascular pathologies, very little is known about how intracellular ionized magnesium (Mgi2+) is regulated by catecholamines. We made an in-vitro study of the variations in the concentration of ionized magnesium in human lymphocytes using the fluorescent probe furaptra in response to different catecholamines. We also made an ex-vivo study of the changes in intracellular ionized magnesium in lymphocytes in 20 subjects with essential arterial hypertension, 10 treated with 120 mg/d of propranolol and 10 with placebo. Norepinephrine and isoproterenol significantly decrease Mgi2+ and this effect is blocked by beta-blockers but not by alpha-blockers. The EC50 of the effect of norepinephrine is within the range of concentrations physiologically present in plasma. The substitution of extracellular sodium with choline blocks the decrease in intracellular ionized magnesium induced by norepinephrine, which leads us to suppose that the magnesium-reducing effect of catecholamines is a result of the activation of a Na+-Mg2+ exchanger. We were not able to demonstrate any change in intracellular ionized magnesium after 1 and 17 days of active treatment in essential hypertensives. The impossibility of demonstrating ex vivo the mechanism of catecholamine-mediated regulation that is evident in vitro is perhaps due to our experimental conditions or to substances which in vivo inhibit the action of the catecholamines on magnesium, such as insulin and/or glucose.

Dopexamine and cellular immune functions during systemic inflammation

An immune-neuroendocrine interaction that is mediated via beta2-adrenergic receptors has been demonstrated previously. Dopexamine is a substance with strong beta2-adrenergic effects and is used in the treatment of critically ill patients. We therefore investigated the effect of dopexamine infusion on survival and cellular immune functions during systemic inflammation. Sepsis (CLP) was induced in male NMRI mice that received either 0.9% saline, dopexamine (0.05 mg/kg/hour ip, DPX), the selective beta2-adrenergic antagonist ICI 118.551 (0.5 mg/kg ip every 12 hours, ICI) or a combination of both drugs. 48 hours after onset of sepsis, survival rate, splenocyte apoptosis, splenocyte proliferation, splenocyte IL-2, IL-6 and IFN-gamma release, and leukocyte distribution were monitored. Dopexamine increased splenocyte apoptosis and normalized the distribution of circulating lymphocytes but did not affect sepsis-induced mortality. ICI 118.551 induced a dramatic increase of mortality paralleled by a decreased splenocyte proliferation and the strongest increase in splenocyte apoptosis. Co-administration of dopexamine abolished the ICI 118.551-induced alterations but this effect seemed to be mediated via a pathway other than adrenergic beta2-receptors. We conclude that dopexamine modulates cellular immune functions during systemic inflammation and that different receptor systems are involved in the mediation of this process. Furthermore, the immunomodulatory effect of beta2-adrenergic blockade was demonstrated.

Heart rate monitoring: applications and limitations

Over the last 20 years, heart rate monitors (HRMs) have become a widely used training aid for a variety of sports. The development of new HRMs has also evolved rapidly during the last two decades. In addition to heart rate (HR) responses to exercise, research has recently focused more on heart rate variability (HRV). Increased HRV has been associated with lower mortality rate and is affected by both age and sex. During graded exercise, the majority of studies show that HRV decreases progressively up to moderate intensities, after which it stabilises. There is abundant evidence from cross-sectional studies that trained individuals have higher HRV than untrained individuals. The results from longitudinal studies are equivocal, with some showing increased HRV after training but an equal number of studies showing no differences. The duration of the training programmes might be one of the factors responsible for the versatility of the results.HRMs are mainly used to determine the exercise intensity of a training session or race. Compared with other indications of exercise intensity, HR is easy to monitor, is relatively cheap and can be used in most situations. In addition, HR and HRV could potentially play a role in the prevention and detection of overtraining. The effects of overreaching on submaximal HR are controversial, with some studies showing decreased rates and others no difference. Maximal HR appears to be decreased in almost all 'overreaching' studies. So far, only few studies have investigated HRV changes after a period of intensified training and no firm conclusions can be drawn from these results. The relationship between HR and oxygen uptake (VO(2)) has been used to predict maximal oxygen uptake (VO(2max)). This method relies upon several assumptions and it has been shown that the results can deviate up to 20% from the true value. The HR-VO(2) relationship is also used to estimate energy expenditure during field conditions. There appears to be general consensus that this method provides a satisfactory estimate of energy expenditure on a group level, but is not very accurate for individual estimations. The relationship between HR and other parameters used to predict and monitor an individual's training status can be influenced by numerous factors. There appears to be a small day-to-day variability in HR and a steady increase during exercise has been observed in most studies. Furthermore, factors such as dehydration and ambient temperature can have a profound effect on the HR-VO(2) relationship.

Does the human heart fatigue subsequent to prolonged exercise?

A reduction in left ventricular systolic and diastolic function subsequent to prolonged exercise in healthy humans, often called exercise-induced cardiac fatigue (EICF), has recently been reported in the literature. However, our current understanding of the exact nature and magnitude of EICF is limited. To date, there is no consensus as to the clinical relevance of such findings and whether such alterations in function are likely to impact upon performance. Much of the existing literature has employed field-based competitions. Whilst ecologically valid, this approach has made it difficult to control many factors such as the duration and intensity of effort, fitness and training status of subjects and environmental conditions. The impact of such variables on EICF has not been fully evaluated and is worthy of further research. To date, most EICF studies have been descriptive, with limited success in elucidating mechanisms. To this end, the assessment of humoral markers of cardiac myocyte or membrane disruption has produced contradictory findings partially due to controversy over the validity of specific assays. It is, therefore, important that future research utilises reliable and valid biochemical techniques to address these aetiological factors as well as develop work on other potential contributors to EICF such as elevated free fatty acid concentrations, free radicals and beta-adrenoceptor down-regulation. In summary, whilst some descriptive evidence of EICF is available, there are large gaps in our knowledge of what specific factors related to exercise might facilitate functional changes. These topics present interesting but complex challenges to future research in this field.

Adhesion molecules, catecholamines and leucocyte redistribution during and following exercise

The circulating blood normally contains no more than 1-2% of the body's population of leucocytes. The numbers and phenotypes of circulating leucocyte subsets can change dramatically during and immediately following exercise. The surface expression of adhesion molecules makes an important contribution to such responses by changing patterns of cell trafficking. Alterations in the surface expression of adhesion molecules could reflect a shedding of molecules, selective apoptosis or differential trafficking of cells with a particular phenotype, effects from mechanical deformation of the cytoplasm, active biochemical processes involving cytokines, catecholamines, glucocorticoids or other hormones, or changes in the induction of adhesion molecules. The expression of adhesion molecules changes with maturation and activation of leucocytes. Typically, mature cells express lower densities of L-selectin (CD62L), the homing receptor for secondary lymphoid organs, and higher densities of LFA-1 (CD11a), the molecule associated with trafficking to non-lymphoid reservoir sites. The neutrophils and natural killer cells that are mobilised during exercise also express high levels of Mac-1 (CD11b), a marker associated with cellular activation. Possibly, exercise demarginates older cells that are awaiting destruction in the spleen. Plasma concentrations of catecholamines rise dramatically with exercise, and there is growing evidence that catecholamines, acting through a cyclic adenosine monophosphate second messenger system, play an important role in modifying the surface expression of adhesion molecules. Analogous changes can be induced by other forms of stress that release catecholamines or by catecholamine infusion, and responses are blocked by beta(2)-blocking agents. Catecholamines also modify adherence and expression of adhesion molecules in vitro. Cell trafficking is modified by genetic deficiencies in the expression of adhesion molecules, but leucocyte responses to exercise and catecholamines are generally unaffected by splenectomy. A number of clinical conditions including atherogenesis and metaplasia are marked by an altered expression of adhesion molecules. The effects of exercise on these molecules could thus have important health implications.

Virus associated immune and pharmacologic mechanisms in disorders of respiratory and cutaneous atopy

Anaphylaxis represents non-atopic immediate hypersensitivity, whereas manifestations of atopic immediate hypersensitivity include bronchial asthma, hay fever, allergic rhinitis, chronic urticaria, and atopic dermatitis. In spite similar antigen exposure, only a minority of the population shown some form of atopic disease. Atopic disease with its spontaneous pattern of familial occurrence cannot be induced at will.

The exact pathogenesis of atopy is yet to be elucidated. Two theories prevail: 1) atopy is a primary disorder of the immune system with sequelae in the various effector tissues; and 2) a concept of atopy as a primary autonomic imbalance, essentially beta adrenergic in character, with sequelae in effector cells, including those engaged in the production of antibodies. The autonomic imbalance is perceived as caused not by some disorder of the autonomic nervous system itself but by a defector functioning of its effector cells. These two concepts are not mutually exclusive. The IgE antibody, which mediates allergic reactions, is essentially identical with atopic reagin in various animal species.

The beta adrenergic theory regards atopic disorders (i.e., perennial and seasonal allergic rhinitis, bronchial asthma, and atopic dermatitis) not as immunologic diseases but as unique patterns of altered reactivities to a broad spectrum of immunologic, psychic, infectious, chemical and physical stimuli. The antigen-antibody interaction is given the same role as that of a broad category of nonspecific stimuli that function only to trigger the same defective homeostatic mechanism in the various effector cells involved in immediate hypersensitivities. Current evidence favors the possibility that there are inherited and/or acquired multiple abnormalities in the receptor—adenylate cyclase—cyclic AMP system of all effector cells that are critical in the organization of immune reactivities.

Atopic abnormality may be 1) acquired by functional receptor regulatory shifts caused by hormonal changes, infection (viral, bacterial, etc), allergic tissue injury or other event; 2) genetically determined; or 3) caused by autoimmune disease. One, two or all three of these effector mechanisms may be operative in a particular disease.

There is an important relationship between asthma and viral respiratory infection. A history of childhood viral respiratory illness is a risk factor for the development of chronic obstructive airway syndromes in later life. Asthmatic attacks occurred only when the infection produced fever, malaise, cough or coryza. The dominant role of fever in these episodes immediately suggests the profound involvement of adrenergic effector mechanisms. The presence of autoantibodies to beta-adrenoceptors in patients correlated well with a reduced beta—and an increased alpha-adrenergic responsiveness. Virus infections can elicit autoantibody formation.

In patients with atopic dermatitis an increased susceptibility and abnormal host response to viral infections in general. Defective cytotoxic T cells, abnormally functioning macrophages and natural killer cells, a reduced production of IFNα in children, and of IFNγ in atopic patients with food allergy has recently been demonstrated. Lymphocytic cyclic AMP-phosphodiesterase, that destroys cyclic AMP, is increased in atopic dermatitis and in allergic respiratory disease of adults, and this increased activity correlated closely with histamine release from basophils. Peripheral blood leukocytes and lymphocytes in atopic dermatitis have frequently demonstrated impaired beta adrenergic reactivity.

Allergic tissue injury may be initiated by antigen-specific IgE antibodies that combine with Fcε receptors on various cell types and trigger mediator release upon encounter with the antigen. Various noxious agents that are capable of triggering asthma are capable of releasing inflammatory mediators from the same target cells. Accounting only for those pharmacologic mediators where the cell-type has been identified, the spectrum of mediator-storing, synthesizing, or transporting cells includes neutrophil leucocytes, basophilic leucocytes eosinophilic leucocytes; mast cells, “chromaffin-positive” mast cells, enterochromaffin cells, chromaffin cells; platelets, neurosecretory cells and nerve cells that potentially produce all amine-mediators as well as prostaglandins and kinins.

Relationship between 24-hour rhythm in antiviral effect of interferon-beta and interferon-alpha/beta receptor expression in mice

The influence of interferon-beta (IFN-beta) dosing time on antiviral activity was investigated in ICR male mice under light-dark cycle conditions (lights on at 07:00, off at 19:00) with food and water available ad libitum. There was a significant dosing time-dependent change in 2',5'-oligoadenylate synthetase (2',5'-OAS) activities, as an index of antiviral activity, in liver at 12 h after IFN-beta (15 MIU/kg, i.v.) injection. IFN-beta-induced 2',5'-OAS activity was more potent after the drug injection during the late dark phase. The higher antiviral effect of IFN-beta was observed when the interferon-alpha/beta receptor (IFNAR) expression in the liver increased, and the lower effect was observed when its expression decreased. IFN-beta-induced fever was more serious after IFN-beta injection from the late dark phase to the early light phase. A significant dosing time-dependent change was demonstrated for plasma IFN-beta concentrations, which showed a higher level during the light phase and a lower level during the dark phase. The dosing time-dependent change of plasma IFN-beta concentrations was not associated with that of the antiviral effect or fever induced by IFN-beta. These results suggest that selecting the most suitable dosing time of IFN-beta, associated with the 24-h rhythm of IFNAR expression in the liver, may be important to increase effectively the antiviral activity of the drug in experimental and clinical situations.

Effects of chronic lesions of the anteroventral region of the third ventricle on cardiac beta-adrenoceptor function in conscious rats

This study examined whether cardiac beta-adrenoceptor (beta-AR) function was altered in conscious rats with lesions surrounding the anteroventral third ventricle (AV3V). The findings were: (1) beta(1,2)-AR-mediated tachycardia was similar in sham and AV3V-lesion rats, (2) beta(3)- and/or atypical beta-AR-mediated tachycardia elicited by isoproterenol (10 microg/kg, i.v.; ISO) was diminished in AV3V-lesion rats treated with beta(1,2)-AR antagonists, but was not in similarly-treated sham-lesion rats, and (3) the tachycardia elicited by the membrane permeable cAMP-analogue, 8-(4-chlorophenylthiol)-cAMP (10 micromol/kg, i.v.), was similar in AV3V- and sham-lesion rats. The possibility that increased plasma sodium/osmolality in AV3V-lesion rats down-regulated cardiac beta(3)- and/or atypical beta-ARs, but not beta(1,2)-ARs or intracellular cAMP signaling is discussed.

Cardiac effects of beta-adrenoceptor antagonists with intrinsic sympathomimetic activity in humans: beta1- and/or beta2-adrenoceptor mediated?

The aim of this study was to find out whether cardiac responses to the beta-adrenoceptor antagonists with intrinsic sympathomimetic activity (ISA) xamoterol and celiprolol are mediated by cardiac beta1- or beta2-adrenoceptors or both. For this purpose we assessed, in six healthy male volunteers, the effects of xamoterol (100 and 200 mg, p.o.) and celiprolol (200, 600, and 1,200 mg, p.o.) on blood pressure, heart rate, and heart rate-corrected duration of the electromechanical systole (QS2c, as a measure of inotropism). Xamoterol, in both doses, increased systolic blood pressure and heart rate, transiently decreased diastolic blood pressure, and shortened QS2c; all these effects were attenuated after pretreatment of the volunteers with the beta1-adrenoceptor antagonist bisoprolol. Celiprolol, in all three doses, increased heart rate, decreased diastolic blood pressure, and shortened QS2c but only marginally increased systolic blood pressure. Bisoprolol did not attenuate these celiprolol effects but rather enhanced celiprolol effects on systolic blood pressure and heart rate. In a further set of experiments, we studied cardiovascular effects of celiprolol in six healthy volunteers whose beta2-adrenoceptors had been desensitized by a 2-week treatment with 3x5 mg/day terbutaline. Under these conditions, celiprolol failed to increase heart rate or to shorten QS2c. We conclude that, under resting conditions, in healthy volunteers, beta-adrenoceptor antagonists with ISA can exert increases in heart rate and contractility that are mediated by either cardiac beta1-adrenoceptor (xamoterol) or cardiac beta2-adrenoceptor (celiprolol) stimulation. Thus in the human heart, the ISA of beta-adrenoceptor antagonists can be a beta1- or beta2-adrenoceptor agonistic component.

Modulation by dietary salt of verapamil disposition in humans

BACKGROUND

The intestine is an increasingly well-recognized site of first-pass drug metabolism. In this study, we determined the influence of dietary salt on the steady-state disposition of verapamil, a drug that undergoes extensive first-pass metabolism.

METHODS AND RESULTS

Eight normal volunteers received 120 mg of racemic verapamil orally twice a day for 21 days. The disposition kinetics of verapamil enantiomers were determined after coadministration of intravenous deuterated verapamil with the morning oral dose on days 7, 14, and 21. Each study day was preceded by 7 days on a fixed-salt diet: in 5 subjects, the initial study was conducted during a low-salt (10 mEq/d) diet, the second study during a high-salt (400 mEq/d) diet, and the third during a low-salt diet, whereas in the other 3 subjects, the sequence of diets was reversed. Plasma concentrations of both unlabeled enantiomers (ie, from oral therapy) were significantly (P<0.05) lower during the high-salt phase (eg, mean area under the time-concentration curve [0 to 12 hours] for S-verapamil: 7765+/-2591 ng. min. mL-1 [high salt] versus 12 514+/-3527 ng. min. mL-1 [low salt], P<0.05). Peak plasma concentrations were significantly lower and the extent of PR interval prolongation significantly blunted with the high-salt diet. In contrast, data with labeled drug (ie, reflecting the intravenous route) were nearly identical for the 2 diets.

CONCLUSIONS

These data indicate that a clinically important component of presystemic drug disposition occurs at the prehepatic (presumably intestinal) level and is sensitive to dietary salt.

A comparison between clenbuterol, salbutamol and terbutaline in relation to receptor binding and in vitro relaxation of equine tracheal muscle

Beta2-adrenoceptor agonists are used as bronchodilators in both humans and horses. Of these drugs, clenbuterol is the one most frequently used when treating chronic obstructive pulmonary disease in the horse, while salbutamol and terbutaline are used in the treatment of human asthma. Little is known of the properties of the latter two drugs in equine medicine. We have compared salbutamol and terbutaline with clenbuterol in relation to their ability to relax muscle strips from equine tracheal muscle, precontracted with 40 nM carbachol, in tissue chambers. The affinities of these drugs to the beta2-adrenoceptors in homogenates of the same muscle tissue were also examined. These experiments were performed with radioligand binding studies using the very potent beta-adrenoceptor antagonist 125I-cyanopindolol. The three drugs were almost equipotent in relaxing the muscle strips. The EC50-values for salbutamol, terbutaline and clenbuterol were 5.6, 13.8 and 2.1 nM, respectively, and all three drugs relaxed the preparations completely. In the competitive binding study, however, the Kd-value of clenbuterol was much lower (24 nM) than that of salbutamol and terbutaline (1100 nM and 3900 nM, respectively). The amount of receptors bound at the EC50-value of clenbuterol was 8% compared to less than 1% for salbutamol and terbutaline. This indicates a lower intrinsic efficacy of clenbuterol than of the other two drugs. The beta-adrenoceptor density was 45 +/- 14.3 fmol/mg protein (mean +/- SD) and the Kd-value of 125I-cyanopindolol was 11.4 +/- 3.3 pM.

Vasoactive drugs inhibit oxygen radical production of neutrophils

A concentration response study was performed to clarify whether vasoactive drugs, routinely used in intensive care patients, inhibit oxygen radical production of neutrophils. Moreover, in a cell-free system, it was investigated whether these drugs exert free radical scavenging properties. Vasoactive agents were incubated with neutrophils from healthy human volunteers, which were stimulated by N-formyl-methionyl-leucyl-phenylalanine (FMLP) and by opsonized zymosan to produce oxygen radicals, detected by chemiluminescence measurements. Sympathomimetics (epinephrine greater than norepinephrine, dopamine and dobutamine) as well as phosphodiesterase-inhibitors (amrinone and enoximone) inhibited FMLP-induced and zymosan-induced oxygen radical production of neutrophils in a concentration-dependent and drug-specific fashion. With the exception of amrinone, FMLP-induced chemiluminescence of neutrophils was impaired nearly 10-fold more markedly than zymosan-induced chemiluminescence. Glyceryl trinitrate, nifedipine and prostacyclin had no effect on oxygen radical production of neutrophils. In the cell-free system, epinephrine, norepinephrine, dopamine, amrinone and enoximone demonstrated oxygen free radical scavenging properties. This study shows that vasoactive drugs, frequently used in the clinical setting, may suppress oxidative burst after FMLP-receptor stimulation. As demonstrated in the cell-free system, this suppression was, at least in part, due to oxygen radical scavenging.

Expression and in-vivo modulation of alpha- and beta-adrenoceptors on human natural killer (CD16+) cells

Expression and in-vivo modulation of beta- and alpha-adrenoceptors on peripheral human natural killer (CD16+) cells was investigated. Ligand binding studies revealed that CD16+ lymphocytes express beta2, alpha1-, alpha2- but not beta1-adrenoceptors. Infusion of adrenaline, but not noradrenaline, significantly decreased beta2- and alpha1-adrenoceptor numbers on NK cells. Both catecholamines did not appreciably alter alpha2-adrenoceptor numbers. Additional analyses showed that adrenaline administration increases alpha2-adrenoceptor numbers on peripheral mononuclear blood cells (PBMC) and T-cell subsets (CD4+, CD8+) in contrast to decreased receptor numbers on CD16+ cells. These data demonstrate a specific effect of increasing levels of circulating catecholamines on beta2-adrenoceptors on NK cells.

Short-term aortic barodenervation diminishes alpha 1-adrenoceptor reactivity in rat aortic smooth muscle

Our previous studies have shown that aortic baroreceptor denervation elicits acute increases in blood pressure and significant elevations of sympathetic activity and peripheral vascular resistance. This study investigated the short-term (3 and 48 h) effect of aortic barodenervation and associated sympathetic hyperactivity on the functional activity of alpha 1-adrenoceptors in rat aortic smooth muscle. Compared with sham operation, aortic barodenervation caused acute rises in blood pressure and heart rate and reductions in baroreflex sensitivity. Blood pressure and heart rate remained elevated when measured in conscious aortic barodenervated rats 3 h after surgery but subsided to sham-operated levels at 48 h; the baroreflex sensitivity, however, remained attenuated. Hexamethonium (0.5-4 mg/kg, i.v.) elicited significantly (P < 0.05) greater depressor responses in conscious aortic barodenervated rats than in sham-operated rats at both 3 and 48 h, suggesting a higher sympathetic activity in denervated rats. Exposure of aortic rings from aortic barodenervated and sham-operated rats to cumulative addition of phenylephrine (alpha 1-adrenoceptor agonist, 3 x 10(-8)-1 x 10(-4) M) resulted in concentration related contractile responses that were similar in the two groups of rats at 3 h in contrast to significantly (P < 0.05) smaller contractions in rings from denervated rats at 48 h. The maximum contraction developed (Emax) at 48 h showed approximately 50% reduction in rings from aortic barodenervated compared with sham-operated rats (239 +/- 16 vs. 558 +/- 15 mg tension/mg tissue). The pA2 value for prazosin (alpha 1-adrenoceptor antagonist) was not altered by aortic barodenervation at 3 h but showed significant (P < 0.05) increases, compared with sham-operated values, at 48 h. It is concluded that short-term aortic barodenervation results in an elevation of sympathetic activity that coincides with reduced responsiveness of aortic smooth muscle to alpha 1-adrenoceptor activation. The aortic barodenervation-induced alpha 1-adrenoceptor desensitization is not a result of decreased receptor affinity but may involve an alteration of receptor density or in the post-receptor activation events.

Intermittent warm blood cardioplegia preserves myocardial beta-adrenergic receptor function

BACKGROUND

Left ventricular dysfunction is frequently observed in patients after hypothermic cardioplegic arrest, and often inotropic intervention is necessary for patients to be successfully weaned from cardiopulmonary bypass (CPB). A myocardial beta-adrenergic receptor (beta AR) desensitization has been noted to occur after hypothermic CPB in patients undergoing coronary artery bypass grafting. This randomized study was undertaken to determine the effect of cardioplegic solution temperature on cardiac beta ARs.

METHODS

Two groups of patients (20 patients in each) scheduled for elective coronary artery bypass grafting underwent CPB with either intermittent warm or cold blood cardioplegia. The density of the beta ARs, the proportion of beta 1- to beta 2-adrenergic receptors, and the beta AR coupling capacity to adenylate cyclase were determined in specimens of the right atrial tissue at baseline, during CPB, and after discontinuation of CPB. Plasma concentrations of catecholamines were also measured in both arterial and coronary sinus samples.

RESULTS

In both cardioplegia groups, no significant modification in either the beta AR density or the proportion of beta 1- to beta 2-adrenergic receptors was detected. However, a significant decrease in adenylate cyclase activity after stimulation with isoproterenol was observed in the cold blood cardioplegia group during CPB (p < 0.01) and 30 minutes after its discontinuation (p < 0.05). Moreover, a significant decrease in adenylate cyclase activity during CPB was detected in this group after stimulation with sodium fluoride (p < 0.05), but this pattern was found to be completely reversed by 30 minutes after discontinuation of CPB. No modification in the basal or stimulated adenylate cyclase activity was observed in the warm blood cardioplegia group during or after CPB.

CONCLUSIONS

Our results confirm the finding from previous studies of a cardiac beta AR desensitization after hypothermic cardioplegic arrest, and provide evidence of the advantages of intermittent warm blood cardioplegia in preserving the autonomic sympathetic function of the heart.

Dietary salt increases first-pass elimination of oral quinidine

BACKGROUND

Some cytochrome P450 (CYP) enzymes, including CYP3A, are expressed not only in the liver but also in the intestine; the latter may therefore be an important site of drug disposition. Animal data suggests that dietary salt modulates expression of renal CYPs. We therefore hypothesized that intestinal CYP3A may be similarly modulated by dietary salt.

METHODS

The effect of changes in dietary salt on the disposition of two CYP3A substrates, quinidine (administered orally and intravenously) and 14C-erythromycin (administered intravenously) were determined after normal volunteers were given high-salt (400 mEq/day) and low-salt (10 mEq/day) diets for 7 to 10 days each.

RESULTS

Plasma concentrations after oral quinidine were significantly lower during the high-salt phase, with the difference between the two treatments attributable to changes within the first 1 to 4 hours after administration. For example, the area under the plasma concentration-time curve for the first hour after drug administration was 0.56 +/- 0.38 microgram.hr/ml for the high-salt diet compared with 1.57 +/- 0.60 micrograms.hr/ml for the low-salt diet (p < 0.05). Similarly, the peak plasma concentration (Cmax) achieved was lower and the time to reach Cmax was later for the high-salt diet (p < 0.05). In contrast, the terminal phase elimination half-lives were similar for the two diets, and no differences in disposition were found with the intravenous drug. The erythromycin breath test was unaffected by the dietary treatments.

CONCLUSIONS

These results indicate an effect of dietary salt on the presystemic disposition of orally administered quinidine. Although the mechanism(s) of CYP3A activity modulation is unknown, this finding may be important in determining drug availability in conditions associated with abnormal salt homeostasis.

Epinephrine-induced changes in serum potassium and cardiac repolarization and effects of pretreatment with propranolol and diltiazem

Although increases in serum epinephrine are known to cause hypokalemia, the epinephrine dosages and concentrations at which this effect occurs, and the electrocardiographic consequences, have not been evaluated. Because epinephrine infusion is now being used to provoke arrhythmias in some patients, we have determined the physiologic effects of a range of dosages of epinephrine. The effects of pretreatment with propranolol and diltiazem on these indexes of epinephrine effect were also evaluated. Epinephrine dose ranging started at 10 ng/kg/min, with doubling of the dose every 10 minutes until a predetermined end point was reached. At the end of each dosage level, serum electrolytes, catecholamines, and an electrocardiogram were recorded. Whereas even the lowest dosage of epinephrine significantly increased heart rate, serum glucose levels increased and serum potassium decreased only when dosages of 160 to 320 ng/kg/min were administered. Plasma concentrations of epinephrine at these dosages were mean +/- SD 1,328 +/- 902 pg/ml, comparable to those observed in these subjects during maximal exercise (1,003 +/- 527 pg/ml). The major electrocardiographic effect of epinephrine infusion was a dose-related increase in QTc, but pretreatment with propranolol blunted this effect and tended to shorten QTc. At an epinephrine dose of 40 ng/kg/min, QTc prolongation persisted and was inhibited by diltiazem. These data suggest that the major electrocardiographic effect of epinephrine infusion is mediated by increased calcium current. At dosages > 80 ng/kg/min, plasma epinephrine concentrations are comparable to those observed with severe stress, and hypokalemia is common. The use of epinephrine as an electrophysiologic provoker at dosages > 80 ng/kg/min results in both a direct effect, as well as an indirect effect due to hypokalemia.

Relationship between alterations in lymphocyte and myocardial beta-adrenoceptor density in patients with left heart valvular disease

1. We have evaluated the possibility that alterations in lymphocyte beta-adrenoceptor density may be related to changes in the myocardial population in left heart valvular diseases. Receptor density and their binding affinities were estimated using [125I]-iodocyanopindolol. 2. The lymphocyte (LC) beta-adrenoceptor density was 43.4 +/- 5.6 fmol/mg protein in the controls (n = 35) and 81% lower in heart valvular patients (n = 86). In myocardial controls (n = 18), the left ventricular (LV) receptor density was 167.2 +/- 29.8 fmol/mg protein, right ventricular (RV) density was 123.1 +/- 14.6 fmol/mg, left atrial (LA) density was 81.6 +/- 10.5 fmol/mg and right atrial (RA) 108.1 +/- 14.5 fmol/mg. Compared with this group, the receptor density of the study patients (n = 47) decreased by 67, 43, 24 and 32% in the LV, RV, LA and RA, respectively. The decrease in LC was twice that of the average total myocardial receptor density. 3. When patients were classified according to their left ventricular load conditions as having either left ventricular pressure overload (LVP), left ventricular volume overload, mixed lesions (MOL) and no left ventricular overload (mitral stenosis; NOL), the attenuation in LC receptor density reached statistical significance for all four groups, without showing significant difference between the individual groups. In contrast, the decrease in all chambers was predominantly due to volume overload. MOL and NOL exerted intermediate effects that were significant in the LV, while LVP did not contribute to the changes in the LA. 4. Accordingly, the reduction in peripheral beta-adrenoceptor density may reflect the extent to which particularly the volume overload exerts its influence on myocardial beta-adrenoceptors in left heart valvular patients.

A sustained increase in beta-adrenoceptors during long-term therapy with metoprolol and bisoprolol in patients with heart failure from idiopathic dilated cardiomyopathy

Effects of long-term therapy with beta 1-selective antagonists (metoprolol, bisoprolol) on beta-adrenoceptors in lymphocytes of patients with idiopathic dilated cardiomyopathy (DCM) were examined. There was a significant reduction in the number of lymphocyte beta-adrenoceptors in patients with DCM compared to that in healthy volunteers, as demonstrated by a selective decrease in maximum number of binding sites (Bmax) for (-)-[125I]iodocyanopindolol (CYP). A therapy with metoprolol and bisoprolol in these patients caused a marked increase in lymphocyte beta-adrenoceptor density. The significant increase was observed from 2 or 3 months after the start of therapy with these drugs, and it was maintained during the therapy for 24 months. The left ventricular ejection fraction in patients with DCM was improved by the long-term therapy with metoprolol and bisoprolol, and this effect seems to be correlated with an observed enhancement of lymphocyte beta-adrenoceptors in the time course. Also, the increase in lymphocyte beta-adrenoceptors appears to be correlated with a gradual amelioration in circulating catecholamine levels by the long-term therapy with beta-adrenoceptor antagonists in patients with DCM. Thus, the present study suggests that beta-adrenoceptors in lymphocytes of patients with DCM are up-regulated by a long-term therapy with metoprolol and bisoprolol.

Dietary sodium intake modulates systemic but not forearm norepinephrine release

INTRODUCTION

Sodium intake has profound effects on systemic and renal sympathetic activity, but its effects on sympathetic activity in skeletal muscle vascular beds, a site at which local regulatory mechanisms could alter vascular tone directly, are unclear.

METHODS

To determine the effect of dietary sodium intake on basal and isoproterenol-stimulated systemic and forearm norepinephrine kinetics, we studied seven healthy male volunteers twice, 4 weeks apart, while they were receiving a low-sodium (10 mmol sodium/24 hours) diet and a high-sodium diet (250 mmol sodium/24 hours). Forearm blood flow, measured by plethysmography, and systemic and forearm norepinephrine spillover, measured by radioisotope dilution, were determined before and after intra-arterial infusion of 60 and 400 ng/min isoproterenol.

RESULTS

Baseline (before isoproterenol) systemic norepinephrine spillover was higher when subjects received the low-sodium diet (448.1 +/- 55.7 ng/min) compared with the high-sodium diet (269.7 +/- 42.7 ng/min; p < 0.05). In contrast, sodium intake did not affect local forearm norepinephrine spillover, either at baseline (low-sodium diet, 2.05 +/- 0.48 ng/min versus high-sodium diet, 2.63 +/- 0.79 ng/min; p = 0.50) or after stimulation with isoproterenol in doses of 60 ng/min (low-sodium diet, 8.84 +/- 2.2 ng/min versus high-sodium diet, 6.1 +/- 1.9 ng/min; p = 0.38) or 400 ng/min (low-sodium diet, 16.4 +/- 4.5 ng/min versus high-sodium diet, 16.7 +/- 2.5 ng/min; p = 0.93).

CONCLUSIONS

Under conditions of low sodium intake, systemic norepinephrine spillover was increased but forearm norepinephrine spillover was not, suggesting that alteration in sodium intake may produce a differential effect on norepinephrine spillover in different tissues but that decreased local sympathetic activity in skeletal muscle is not the likely mechanism by which a low-sodium diet may lower blood pressure or attenuate stress-induced pressor responses.

Forearm beta adrenergic receptor-mediated vasodilation is impaired, without alteration of forearm norepinephrine spillover, in borderline hypertension

Impaired beta adrenoceptor-mediated vasodilation associated with enhanced sympathetic activity has been reported in established hypertension. We examined whether altered beta adrenoceptor-mediated vasodilation occurs early in the disease process, when structural vascular changes are likely to be less marked, by measurement of forearm blood flow by strain gauge plethysmography after the intraarterial administration of increasing doses of a beta receptor agonist, isoproterenol, in eight subjects with borderline hypertension (BHT) and 13 normotensive (NT) controls. To determine the role of sympathetic activation in the regulation of responsiveness, we measured local sympathetic activity in the forearm by a radioisotope dilution technique. Vasodilation in response to isoproterenol, measured either as changes in forearm blood flow or forearm vascular resistance, was impaired in the BHT group so that flow at the highest dose of isoproterenol (400 ng/min) increased less (15.2 +/- 1.5 ml/100 ml per min) than in the NT group (24.4 +/- 2.4 ml/100 ml per minute) (P < 0.001). Although, systemic norepinephrine spillover was significantly greater in BHT, the difference in blood flow response to isoproterenol was not accounted for by increased local sympathetic activity since forearm norepinephrine spillover at baseline (BHT 1.0 +/- 0.4 ng/min vs. NT 0.64 +/- 0.13 ng/min) and after the administration of isoproterenol 60 ng/min (BHT 5.2 +/- 1.4 ng/min vs. NT 6.0 +/- 1.5 ng/min) and 400 ng/min (BHT 13.5 +/- 2.9 ng/min vs. NT 16.5 +/- 2.7 ng/min) did not differ between the two groups. We therefore conclude that vasodilation in response to isoproterenol is impaired in subjects with BHT and that this impairment is not explained by locally increased basal, or stimulated, sympathetic activity.

Tachyphylaxis of human forearm vascular responses does not occur rapidly after exposure to isoproterenol

In vitro and limited in vivo data suggest that rapid desensitization of beta-adrenoceptor responses occurs after exposure to agonist. Tachyphylaxis to a beta-adrenoceptor agonist would represent a potentially important mechanism for the short-term regulation of vascular tone. The effects of a 4-hour infusion of 400 ng/min intra-arterial isoproterenol on forearm blood flow and presynaptic beta-adrenoceptor-mediated norepinephrine release were determined in eight healthy volunteers. Intra-arterial isoproterenol at 400 ng/min resulted in a significant increase in forearm blood flow in all eight subjects at all time points, with no evidence of tachyphylaxis. In fact, forearm blood flow after 4 hours of the isoproterenol infusion (22.8 +/- 3.3 mL/100 mL per minute) was significantly greater than after 7 minutes (14.6 +/- 2.8 mL/100 mL per minute), 15 minutes (15.4 +/- 2.4 mL/100 mL per minute), and 30 minutes (17.4 +/- 3.0 mL/100 mL per minute) of the infusion (P < .05). Similarly, presynaptic beta-adrenoceptor responses showed no evidence of tachyphylaxis, so forearm norepinephrine spillover values after 7 minutes (6.6 +/- 0.94 ng/min), 15 minutes (7.6 +/- 1.5 ng/min), and 4 hours (8.8 +/- 1.1 ng/min) of isoproterenol infusion were increased and similar. Minimal systemic effects were observed, and there was no evidence of tolerance, there being no difference in heart rate after 7 minutes (70.7 +/- 2.7 beats per minute) and 4 hours (72.2 +/- 3.6 beats per minute) of isoproterenol infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced adenylyl cyclase activation with no decrease in beta-adrenergic receptors in basenji greyhound leukocytes: relevance to beta-adrenergic responses in airway smooth muscle

Mononuclear leukocytes (MNLs) have been used as a model of beta-adrenergic responsiveness of airway smooth muscle, but the relevance of this model remains controversial. The basenji greyhound (BG) dog model of airway hyperresponsiveness shares some features with human asthma, and airway smooth muscle shows a selective impairment in isoproterenol-stimulated adenylyl cyclase activity. In this study, MNL membranes were obtained from these same dogs, and the beta-adrenergic receptor-adenylyl cyclase cascade function was compared with that in airway smooth muscle. beta-Adrenergic receptor numbers and affinities for iodine 125-cyanopindolol were similar in the two dog groups (receptor numbers [Bmax] = 441 +/- 101 and 447 +/- 61 fmol/mg protein and dissociation constant [Kd] = 269 +/- 44 and 312 +/- 60 pmol/L for mongrel and BG MNLs, respectively). Quantities of the Gs alpha protein were not different in the membranes as determined by immunoblotting. Stimulation of adenylyl cyclase by isoproterenol (100 mumol/L) was impaired in MNL membranes of BG membranes (22% +/- 4% increase over guanosine triphosphate [10 mumol/L]) compared with mongrel membranes (47% +/- 8.6% increase over guanosine triphosphate [10 mumol/L], p < 0.05). Stimulation of adenylyl cyclase by prostaglandin E1 (10 mumol/L), NaF (10 mmol/L), or forskolin (10 mumol/L) did not differ in membranes from the two groups. No difference was found in the lymphocyte subsets in the two groups as determined by flow cytometry. These findings are qualitatively similar to studies of trachealis muscle membranes from these same dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Reversible decrease of surface beta 2-adrenoceptor number and response in lymphocytes of patients with pheochromocytoma

To study the effect of chronic exposure to elevated plasma catecholamines on surface beta 2-adrenoceptor density, we measured these receptors in the lymphocytes of 9 patients with pheochromocytoma as well as in 27 healthy control subjects. Binding experiments were performed on intact lymphocytes using the hydrophilic ligand [3H]-CGP12177. Lymphocyte beta 2-adrenergic response was also measured in three patients. beta 2-adrenoceptor density (p < 0.01), and isoproterenol-stimulated increase in cAMP were reduced in patients with pheochromocytoma. Both parameters normalized (p < 0.05) when patients were reevaluated 4 weeks after tumor removal, coinciding with normalization of plasma epinephrine (r = -0.95, p < 0.01) and to log of plasma norepinephrine (r = -0.58, p < 0.05) in patients. We conclude that chronic catecholamine excess induces a decrease of lymphocyte beta 2-adrenoceptor surface number and response that is reversible upon normalization of plasma catecholamine levels. This regulation is mainly dependent on plasma levels of the hormone epinephrine, but norepinephrine may also play a regulatory role at supraphysiological levels.

Racial differences in epinephrine and beta 2-adrenergic receptors

This study examined the effects of ethnicity and hypertension on beta 2-adrenergic receptors and on plasma catecholamines in a group of 77 unmedicated mildly hypertensive and normotensive men. Black hypertensive subjects had the most sensitive and white hypertensive subjects the least sensitive beta-receptors (as assessed by isoproterenol-stimulated cyclic AMP in lymphocytes [P = .02]). In contrast, postreceptor adenylate cyclase activation (as assessed by forskolin stimulation) was similar among groups. As with beta-receptor sensitivity, black hypertensive subjects had the highest beta-receptor density and white hypertensive subjects the lowest (P = .03). Blacks demonstrated lower plasma epinephrine values compared with whites (P = .03). Across all subjects, plasma epinephrine was negatively correlated with beta-receptor density (r = -.26, P < .05) and sensitivity (r = -.25, P < .05). There were no group differences in binding affinity to the beta-antagonist iodopindolol. The findings support the notion of increased beta-adrenergic receptors in hypertension in blacks.

Catecholamines, lymphocyte subsets, and cyclic adenosine monophosphate production in mononuclear cells and CD4+ cells in response to submaximal resistance exercise

We examined the effect of 30 min of submaximal resistance exercise on free and sulphoconjugated plasma catecholamine concentrations determined by high performance (-pressure) liquid chromatography separation, the distribution of circulating lymphocytes quantified by flow cytometry, and isoproterenol induced cyclic adenosine monophosphate (cAMP) production in mononuclear cells (MNL) and CD4+ cells. Venous blood samples were taken before, immediately after and 45 min after exercise. Resistance exercise increased free plasma adrenaline (A) and noradrenaline (NA) concentrations, whereas sulphoconjugated catecholamine concentrations remained unchanged. Exercise induced leucocytosis and lymphocytosis was predominantly manifested by an increase in the number of total lymphocytes, monocytes, CD3+, CD8+ cells and CD3- CD16/CD56+ cells. Redistribution resulted in a decrease in the CD4+:CD8+ ratio. The total number and distribution of lymphocytes returned to baseline after 45-min rest. An exercise-induced increase in the number of CD3- CD16/CD56+ cells was significantly correlated with the increase in plasma NA (r = 0.66; P = 0.035), indicating a NA dependent process of redistribution. The cAMP-production in MNL was significantly elevated after resistance exercise, when cells were stimulated with 1 mumol.1(-1) isoproterenol [pre-exercise 16.5 (SD 3.3); postexercise 21.6 (SD 9.8); 45 min postexercise 10.7 (SD 2.8)]. The cAMP production in CD4+ cells was not affected by exercise. Therefore, it is discussed whether redistribution is responsible for the exercise induced increase in cAMP production in MNL.

Age-related changes in beta-adrenergic neuroeffector systems in the human heart

BACKGROUND

Aging decreases cardiac beta-adrenergic responsiveness in model systems and in humans in vivo. The purpose of this study was to comprehensively evaluate the age-related changes in the beta-receptor-G protein-adenylyl cyclase complex in nonfailing human hearts.

METHODS AND RESULTS

Twenty-six nonfailing explanted human hearts aged 1 to 71 years were obtained from organ donors and subjected to pharmacological investigation of beta-adrenergic neuroeffector systems. When the population was subdivided into the 13 youngest and 13 oldest subjects, total beta-receptor density assessed by maximum [125I]ICYP binding (beta max) was reduced in older hearts by 37% in left ventricles and 31% in right ventricles (both P < .05), and the downregulation was confined to the beta 1 subtype (r = .78 left ventricle beta 1 density versus donor age). Older donor hearts exhibited a 3- to 4-fold rightward shift of ICYP-isoproterenol (ISO) competition curves and demonstrated 43% fewer receptors in a high-affinity agonist binding state (P < .05). Older hearts exhibited decreased adenylyl cyclase stimulation by ISO, by zinterol (beta 2-agonist), and by the G protein-sensitive probes forskolin, Gpp(NH)p, and NaF. In contrast, there was no change in response to manganese, a specific activator of the adenylyl cyclase catalytic subunit. Toxin-catalyzed ADP ribosylation in membranes prepared from older versus younger hearts revealed a 29% to 30% reduction (P < .05) with cholera toxin (Gs) but no difference with pertussis toxin (Gi). The systolic contractile response of isolated right ventricular trabeculae to ISO was decreased by 46%, with a 10-fold increase in ISO EC50 in older relative to younger donor hearts.

CONCLUSIONS

There is a profound decrease in cardiac beta-adrenergic responsiveness with aging. This occurs by multiple mechanisms including downregulation and decreased agonist binding of beta 1-receptors, uncoupling of beta 2-receptors, and abnormal G protein-mediated signal transduction.

Clinical efficacy and safety of clenbuterol HCl when administered to effect in horses with chronic obstructive pulmonary disease (COPD)

A field study of 239 horses was conducted to determine the efficacy and safety of clenbuterol HCl, a beta 2-adrenergic bronchodilator, when administered incrementally to effect in the treatment of chronic obstructive pulmonary disease (COPD). The severity of COPD (heaves) and response to treatment was determined by clinical evaluation; an overall 'heaveiness rating' (OHR) was assigned at each observation. The horses were treated orally b.i.d. with clenbuterol (as Ventipulmin Syrup), beginning with the lowest dosage of 0.8 micrograms/kg. On day 10 of treatment at the effective dose (0.8, 1.6, 2.4 or 3.2 micrograms/kg), treatment was either withdrawn (Schedule A) or continued for an additional 20 days (Schedule B). Horses on Schedule A demonstrated a significant improvement in the mean OHR on treatment Day 10 compared to the baseline overall heaveiness rating (BOHR) and a significant increase in the mean OHR (relapse) after the drug was withdrawn. Schedule B horses showed significant improvement (compared to BOHR) on treatment Days 10, 20 and 30. Incremental dosing with clenbuterol provided clinical improvement in 75% of the horses with a lower 95% confidence limit of 71%. Twenty-five percent were nonresponders. A greater percentage of the more severely affected horses required the 3.2 micrograms/kg dosage or were nonresponders compared to horses with a lower BOHR. Side effects of sweating, muscle tremor, and nervousness were of low intensity (mild to moderate) and frequency (< 7% of all observations) due to the regimen of incremental dosing to effect.

Relation between lymphocyte beta-adrenergic responsivity and the severity of depressive disorders

Basal level and isoproterenol-induced response of cyclic adenosine monophosphate (cAMP) were determined in mononuclear leucocytes from 17 drug-free patients with major depressive (n = 9) or dysthymic disorders (n = 8) and 20 normal controls. No significant difference was observed between basal cAMP levels from depressed and control subjects. The cAMP production in response to maximal stimulation by isoproterenol (ISO), a beta-agonist, was significantly lower (-34.7%) in depressed patients than in controls, and was significantly negatively correlated to the severity of the depression as assessed by the Hamilton depression rating scale score (r = -0.62; p < 0.003). When the depressed group was subdivided on the basis of the DSM-III-R (APA 1987) diagnosis criteria into major depressive and dysthymic disorders, the ISO-stimulated cAMP levels in the two groups were indistinguishable. When evaluated at the same time than the density of beta-adrenoreceptors in eight depressed patients, the ISO-stimulated cAMP levels were highly significantly correlated with the Bmax values (r = 0.89; p < 0.003). The results indicate that the decrease in beta-adrenergic responsiveness of mononuclear leukocytes can be present in depressed patients whatever the nosographical subtype of the depressive disorder and is quantitatively related to the depression severity. Based on these data, it seems that the blunted beta-adrenergic sensitivity observed in mononuclear leukocytes (MNL) cells of depressed patients is closely associated with a loss of beta-adrenoceptors.

A new dosing regimen for esmolol to treat supraventricular tachyarrhythmia in Chinese patients

OBJECTIVES

The purpose of this study was to find a safe dosing regimen for esmolol infusion to rapidly control supraventricular tachyarrhythmia after cardiac surgery in Chinese patients.

BACKGROUND

Tachycardia increases cardiac work but reduces myocardial perfusion. Thus, in the critical period immediately after cardiac surgery, tachycardia itself warrants urgent intervention. Esmolol, an ultrashort-acting beta-adrenergic blocking agent, has been reported in western published reports to have good results and few side effects in the treatment of supraventricular tachyarrhythmia. However, its clinical application in Chinese patients has not yet been reported.

METHODS

When supraventricular tachyarrhythmia with a rapid ventricular response (> 110/min) was found early after cardiac surgery, esmolol infusion with a different dosing regimen was used to control the tachyarrhythmia.

RESULTS

With the dosing regimen recommended in western published reports (repeated loading infusion with stepwise increment), acute hypotension with systolic pressure < 80 mm Hg occurred in all six patients after 1 min of loading infusion of esmolol (500 micrograms/kg body weight per min). To avoid the aforementioned complications, a new dosing regimen was constructed. The initial infusion rate of esmolol was set at 150 or 100 micrograms/kg per min, depending on the patient's age and blood pressure. When the desired heart rate was achieved, the initial infusion rate was reduced to the maintenance infusion rate to maintain the therapeutic effect [Maintenance infusion rate = Initial infusion rate x (1 - e-0.077t), where t is the time period in minutes required by the initial infusion of esmolol to achieve the therapeutic effect]. With this new dosing regimen, tachycardia in most patients (9 of 11) could be controlled within 10 min, and no one experienced the side effect of hypotension. The maintenance infusion rate of esmolol needed to control supraventricular tachyarrhythmia in our patients was only 73 +/- 42 micrograms/kg per min (mean +/- SD), much less than that noted in western reports.

CONCLUSIONS

The dosing regimen for esmolol infusion recommended in western studies is not suitable for Chinese patients. In this report we propose a new dosing regimen for esmolol infusion that is both safe and rapid in the treatment of supraventricular tachyarrhythmia in Chinese patients.

The lymphoblast beta-adrenergic receptor in bipolar depressed patients: characterization and down-regulation

beta-Adrenergic receptor binding and adenylyl cyclase activity were examined in lymphoblast cell lines established from 12 patients with bipolar disorder and 10 unrelated healthy control subjects. No significant differences were found in [125I]iodocyanopindolol binding affinity or capacity or in isoprenaline-stimulated cAMP response. Incubation of lymphoblasts with isoprenaline (1 nM) for 24 h prior to assay reduced both receptor number and adenylyl cyclase activity. The extent of receptor down-regulation was significantly less in cells of bipolar disorder patients (20 +/- 5%) compared to controls (40 +/- 4%). Desensitization of adenylyl cyclase, however, was reduced to a similar degree in bipolar (65 +/- 14%) and control (68 +/- 20%) subjects. We conclude that basal beta-adrenergic receptor characteristics are not altered in bipolar disorder but that agonist down-regulation of receptor number may be less efficient than in control cells. The functional implications of this effect are discussed.

Increased high affinity beta-adrenergic receptor densities and cyclic AMP responses of CD8 cells in multiple sclerosis

Beta-adrenergic receptor (beta R) density is increased on suppressor T-cells (Ts) from patients with chronic progressive multiple sclerosis (CPMS). We investigated the contribution of high-affinity (kh) beta R to cAMP responses of nongranular leukocyte subsets from CPMS patients and normal individuals (NL). CD8 beta R density was 1930 receptors/cell in CPMS compared to only 1020 receptors/cell in NL (t(18) = 2.73, P < 0.02). beta R densities on monocytes, B cells, and CD4 cells did not differ between groups. The increased density of beta R on CD8 cells in CPMS was entirely the result of an increase in the number of high affinity receptors. Basal level of cAMP in CD8 lymphocytes were 7.8 pmol/10(6) cells in CPMS and 3.5 pmol/10(6) cells in NL. Isoproterenol stimulation elevated cAMP levels in CD8 cells to 49.9 pmol/10(6) cells in CPMS patients and to 25.7 pmol/10(6) cells in NL (difference after activation: t(18) = 3.23, P < 0.005). No differences between groups were found in cAMP levels of other cell subsets. We also measured circulating catecholamine levels. Supine and standing epinephrine levels were not different between CPMS and NL. Supine norepinephrine (NE) levels were higher in CPMS (411 pg/ml) than in NL (268 pg/ml) (P < 0.03); upon standing, significant increases in NE occurred in both groups to 573 pg/ml in CPMS and to 494 pg/ml in NL. These results extend our previous findings of peripheral sympathetic dysregulation in CPMS and suggest a means whereby Ts function, hypothesized to play a role in the immune pathogenesis of CPMS, may be altered.

Beta-receptor responsiveness after desipramine treatment

To examine whether a tricyclic antidepressant affects the functional response to a beta-receptor agonist in man, the response of heart rate, blood pressure, and plasma cAMP to isoproterenol was measured in 14 normal controls taking 75 mg desipramine daily. Desipramine significantly increased the bolus dose of isoproterenol needed to increase heart rate by 25 bpm at 14-30 days but not at 3-8 days. During infusions of isoproterenol, the increase in systolic blood pressure was blunted at both 3-8 days and 14-30 days, while the decrease in diastolic blood pressure was unaffected. Blood pressure findings were not affected by preadministration of bethanechol. In ten controls, isoproterenol infusions increased plasma cAMP, but this was unaffected by desipramine treatment. These findings suggest a decrease in the functional response of beta 1, but not beta 2, receptors after treatment with desipramine.

Alpha- and beta-adrenergic receptors in children with essential hypertension

Platelet alpha 2- and lymphocyte beta-adrenergic receptors were examined in eight children aged 10-16 years with essential hypertension, and in 11 age-matched normotensive children. Both alpha 2- and beta-adrenergic receptor concentrations showed no significant differences between children with essential hypertension and normotensive children. According to other studies, physiological fluctuations in catecholamines determine lymphocyte beta-adrenergic receptor concentrations, although down-regulation in platelet alpha 2-adrenergic receptors has not been observed. The present findings suggest that there may be no abnormalities in alpha 2- and beta-adrenergic receptors in essential hypertension in childhood, although a hyperadrenergic state has been reported to be of some relevance to the pathogenesis of essential hypertension in young adolescents.