Beta-adrenoceptor density in chronic infarcted myocardium: a subtype specific decrease of beta1-adrenoceptor density

Beta-adrenoceptor density is altered in different cardiac diseases. In heart failure beta-adrenoceptor density is down regulated but in acute myocardial ischemia beta-adrenoceptor density is up regulated. In hearts with myocardial infarction total beta-adrenoceptor density is decreased shortly after myocardial infarction. AIMS AND METHODS: To investigate whether total beta-adrenoceptor number is altered in the chronic phase after myocardial infarction, and to identify the specificity of alteration, we studied male Wistar rats (n = 18) which underwent a ligation of the left coronary artery or a sham operation. Twelve weeks after coronary ligation, rats were sacrificed and hearts were excised, perfused to obtain blood-free myocardium and frozen in liquid nitrogen. Infarcted myocardium was identified visually and separated from non-infarcted myocardium. Total beta-adrenoceptor number was calculated in fmol (-)-[125I]iodocyanopindolol specifically bound/mg protein and the relative amount of beta1- and beta2-adrenoceptor density was measured by inhibition of (-)-[125I]iodocyanopindolol binding with CGP 20712 A. RESULTS: Total beta-adrenoceptor number in infarcted myocardium was significantly decreased (25.7+/-1.4 vs. 24.9+/-2.2 vs. 20.1+/-3.2 fmol/mg protein (P=0.03) resp. Sham vs. Non-infarcted vs. Infarcted myocardium), due to a decrease of only beta1-adrenoceptor density (14.7+/-0.61 vs. 12.7+/-1.09 vs. 4.84+/-0.96 fmol/mg protein (P=0.004) resp.), whereas the beta2-adrenoceptor density and the dissociation constant (Kd) were not significantly decreased. CONCLUSION: In the infarcted myocardium total beta-adrenoceptor density is decreased due to a decreased beta1-adrenoceptor density at 12 weeks after myocardial infarction.     

Influence of beta blockade on exercise capacity and heart rate response after human orthotopic and heterotopic cardiac transplantation

It has been reported that use of beta blockers may not be safe after cardiac transplantation because the denervated hearts may be largely dependent on circulating catecholamines to increase cardiac output. Therefore, the effects of intravenous propranolol were studied during maximal treadmill exercise in 7 patients with heterotopic and 6 with orthotopic cardiac transplantations. An average decrease of about 15% in exercise duration (p less than 0.001), a 34% reduction in systolic blood pressure increase (p less than 0.05) and a 40% attenuation in heart rate increase (p less than 0.001) were observed after beta blockade. In patients with heterotopic transplantation, beta blockade produced similar effects on heart rate in the denervated donor hearts and the innervated recipient hearts during and after mild exercise. During peak exercise, beta blockade attenuated the rate to a greater extent in the donor hearts. Although the denervated donor heart is more sensitive to beta blockade than the innervated recipient heart during exercise, no adverse effects were observed. Beta-blocker therapy should be considered for cardiac transplant patients if longer-term studies confirm their safe use in these patients.     

Myocardial dysfunction in donor hearts. A possible etiology.

BACKGROUND: Potential cardiac donors show various degrees of myocardial dysfunction, and the most severely affected hearts are unsuitable for transplantation. The cause of this acute heart failure is poorly understood. We investigated whether alterations in calcium-handling proteins, beta-adrenoceptor density, or the inhibitory G protein Gialpha could account for this phenomenon in unused donor hearts (n=4 to 8). We compared these with end-stage failing hearts (n=14 to 16) and nonfailing hearts (n=3 to 12). METHODS AND RESULTS: Myocardial samples were obtained from unused donor hearts displaying ejection fractions <30%. Both trabeculae and isolated myocytes responded as poorly as those from the group of failing hearts to increasing stimulation frequency with regard to inotropic function in vitro. Immunodetectable abundance of sarcoplasmic reticulum calcium-ATPase and sodium calcium exchanger were greater (177%; P<0.01) and smaller (29%; P<0.01), respectively, in the unused donor hearts relative to the failing group, which suggests that alterations of these proteins are not a common cause of contractile dysfunction in the 2 groups. Myocytes from the unused donor group were desensitized to isoprenaline to a similar degree as those from the failing heart group. However, beta-adrenoceptor density was reduced in the failing (P<0.001) but not in the unused donor heart group (P=0.37) relative to the nonfailing heart group (n=5). Gialpha activity was increased in samples from unused donor and failing hearts relative to nonfailing hearts (P<0.05). CONCLUSIONS: Increased activity of the inhibitory G protein Gialpha is a significant contributory factor for impaired contractility in these acutely failing donor hearts.     

Specific removal of beta1-adrenoceptor autoantibodies by immunoabsorption in rabbits with autoimmune cardiomyopathy improved cardiac structure and function

Growing evidence suggests that the beta1-adrenoceptor-directed autoimmune mechanism may play an important role in the pathogenesis of idiopathic dilated cardiomyopathy. The aim of this study is to further study the effect of specific immunoabsorption of anti-beta1-adrenoceptor autoantibodies on cardiac structure and function in autoimmune cardiomyopathy in rabbits. Twenty-four male rabbits were divided into 2 groups: (1) one immunized with beta1-adrenoceptor peptide (beta1 group, n=16), and (2) the other receiving saline injection as a control (control group, n=8). Immunization was performed once a month for 8 months. A high concentration of anti-beta1-adrenoceptor autoantibodies was exhibited throughout the immunization period. Rabbits in the beta1 group showed increased left ventricular end-diastolic diameter (LVDd), decreased left ventricular ejection fraction (LVEF) and increased LV mass/body weight ratio after the 8th month. Immunoabsorption with beta1-adrenoceptor peptide column was able to remove up to 35% of anti-beta1-adrenoceptor autoantibodies in 2 h, resulting in decreased LVDd and increased LVEF 3 months after. Specific removal of anti-beta1-adrenoceptor autoantibodies improved cardiac structure and function in experimental autoimmune cardiomyopathy. These results suggest that anti-beta1-adrenoceptor autoantibodies are of pathogenic importance in the induction of cardiomyopathy, and that specific immunoabsorption as an emerging therapy may be considered when anti-beta1-adrenoceptor autoantibodies are pathophysiologically involved.     

Myocardial beta-adrenoceptor changes in heart failure: concomitant reduction in beta 1- and beta 2-adrenoceptor function related to the degree of heart failure in patients with mitral valve disease

In patients suffering from end-stage congestive cardiomyopathy, cardiac beta 1-adrenoceptor function is markedly reduced, whereas cardiac beta 2-adrenoceptor function is nearly normal. To determine whether beta 1-adrenoceptor function is impaired in heart failure selectively, beta 1- and beta 2-adrenoceptor density and functional responsiveness in the right and left atria and the left papillary muscles from patients with mitral valve disease (functional class III to IV) were studied. In all three tissues concomitantly beta 1- and beta 2-adrenoceptor density gradually declined when the degree of heart failure increased from functional class III to IV. This decrease in beta 1- and beta 2-adrenoceptor density was accompanied by similar decreases in the contractile response of isolated electrically driven right atrial and left ventricular papillary muscles to beta-adrenergic agonists. It is concluded that a decrease in cardiac beta-adrenoceptor function is a general phenomenon in heart failure, and its extent is related to the degree of heart failure. However, in contrast to congestive cardiomyopathy, in mitral valve disease the decrease in cardiac beta-adrenoceptor function is due to a concomitant decrease in beta 1- and beta 2-adrenoceptors.     

Autocrine regulation of TGF beta expression in adult cardiomyocytes

As shown before, TGF beta acts in an autocrine manner on the induction of hypertrophic responsiveness to beta-adrenoceptor stimulation in cultured ventricular cardiomyocytes of adult rat. We now investigated how TGF beta expression and activation is regulated in these cultures and how beta-adrenoceptor stimulation influences TGF beta -mRNA expression. It was found that freshly isolated cardiomyocytes secrete latent TGF beta in the culture medium. Supplementation of the cultures with 20% FCS resulted in activation of the secreted TGF beta to 4.1+/-0.2 ng/ml active TGF beta after 6 days. Presence of the protease inhibitor aprotinin (50 microg/ml) reduced TGF beta activity by 44+/-5% (n=5, P<0.05). In cultures supplemented with 5% FCS, TGF beta was not activated. Active TGF beta downregulated its mRNA-expression: after 6 days TGF beta(1)-mRNA was reduced to 55.1+/-11.0%, TGF beta(2)-mRNA to 30.1+/-16.5%, and TGF beta(3)-mRNA to 0.3+/-0.4% in 20% FCS-cultures as compared to their expression in freshly isolated cells (n=4, P<0.05). TGF beta-mRNA expression did not change in cultures without active TGF beta. Isoprenaline (1 microm) increased TGF beta(1)-mRNA only in cultures which had been pre-exposed to active TGF beta. This effect was also seen when hearts from normal mice were compared with hearts from transgenic mice overexpressing TGF beta(1): only in hearts from transgenic animals perfusion with isoprenaline increased TGF beta(1)-mRNA. In conclusion, isolated cardiomyocytes release latent TGF beta, which is activated by external proteases. Active TGF beta downregulates its own mRNA expression. Preexposure to TGF beta is necessary for a beta-adrenoceptor-mediated increase in TGF beta(1)-mRNA in cardiomyocytes.     

The functional importance of beta 1 and beta 2 adrenoceptors in the human heart

Radioligand binding studies have demonstrated convincingly the coexistence of beta 1 and beta 2 adrenoceptors in the human heart. Both subtypes are involved in the increase in tissue levels of cyclic adenosine monophosphate in isolated, electrically driven, human right atria and in the activation of adenylate cyclase in human cardiac membrane preparations. In isolated, electrically driven strips of human right atria, isoproterenol increased contractile force through stimulation of both beta 1 and beta 2 adrenoceptors, while the selective beta 2-adrenoceptor agonist, procaterol, caused its positive inotropic effect predominantly through beta 2-adrenoceptor stimulation. Norepinephrine, however, increased contractile force solely via beta 1-adrenoceptor stimulation. In this preparation, dobutamine also acted as a full agonist, producing a positive inotropic effect through stimulation of both beta-adrenoceptor subtypes. Dopexamine hydrochloride, on the other hand, having an approximately 10-fold greater affinity for right atrial beta 2 than for beta 1 adrenoceptors, acted as a partial agonist (maximal positive inotropic effect: about 30% that of isoproterenol). Similar effects have been obtained in human right and left ventricular strips; thus, there can be no doubt that cardiac beta 2 adrenoceptors can contribute to the positive inotropic effects of beta-adrenoceptor agonists in the human heart. Besides mediating positive inotropic effects, right atrial beta 2 adrenoceptors may be involved in the regulation of heart rate since, in healthy volunteers, the selective beta 2-adrenoceptor antagonist, ICI 118,551, was more potent than the selective beta 1-adrenoceptor antagonist, bisoprolol, in antagonizing isoproterenol-induced tachycardia, when both antagonists were administered in doses that selectively occupied more than 90% of beta 2 and beta 1 adrenoceptors, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in cardiac beta 1- and beta 2-adrenoceptor densities after human cardiac transplantation: relation to transplant coronary vasculopathy and pretransplantation disease.

In 100 patients 12 to 60 months after cardiac transplantation, the influence of transplant coronary vasculopathy and of the pretransplantation disease (end-stage heart failure caused by coronary artery disease or dilated cardiomyopathy) on the beta-adrenergic receptor (AR) numbers and beta 1/beta 2-AR ratio of right ventricular biopsies was determined. Patients with coronary vasculopathy (CVP) after cardiac transplantation had lower absolute numbers of beta 1-AR compared with patients without CVP. Since patients with CVP had increased left ventricular (LV) end-diastolic pressure and LV muscle mass, it is suggested that decreased beta 1-AR may be the result of an altered hemodynamic situation of the transplanted heart after development of CVP. Patients with dilated cardiomyopathy (DCM) before cardiac transplantation showed a decrease in total beta-AR and of the beta 1/beta 2-AR ratio as a result of an increase in beta 2-AR and a decrease in beta 1-AR numbers. The decreased beta 1/beta 2-AR ratio in patients with previous DCM may indicate that the beta-AR system of the transplanted heart might be influenced (at least in part) by pathophysiologic factors that are characteristic of the pretransplantation disease ultimately leading to cardiac transplantation and persisting after cardiac transplantation.     

Beta-adrenergic control of motility in the rat colon. II. Proportions of beta 1- and beta 2-adrenoceptors identified with 125I-(-)pindolol binding

The specific binding of 125I-(-)pindolol to membranes prepared from rat colon displayed high affinity (Kd = 75 +/- 3 pM) and relatively low capacity (Bmax = 48 +/- 3.8 fmol/mg protein). Furthermore, the binding was reversible and possessed properties expected of a beta-adrenoceptor. Thus, for example, the potency of agonists in displacing 125I-(-)pindolol was, in decreasing order, isoproterenol greater than epinephrine greater than norepinephrine, and the negative isomer of propranolol was two orders of magnitude more potent than the positive isomer. Displacement of specific binding by the beta 1-adrenoceptor antagonist pafenolol and the beta 2-adrenoceptor antagonist ICI 118.551 revealed that the colon preparation possessed a heterogenous beta-adrenoceptor population. Analysis of the inhibition curves using computer-assisted curve fitting suggested that the sites consisted of a small (14%-21%) beta 1-adrenoceptor population and a large (79%-86%) beta 2-adrenoceptor population. The coexistence of beta 1- and beta 2-adrenoceptors is discussed in relation to evidence of a functional linkage of both subtypes with colon motility.     

Second allogeneic haematopoietic stem cell transplantation in relapsed acute and chronic leukaemias for patients who underwent a first allogeneic bone marrow transplantation: a survey of the Société Française de Greffe de moelle (SFGM)

Although recurrent malignancy is the most frequent indication for second stem cell transplantation (2nd SCT), there are few reports that include sufficiently large numbers of patients to enable prognostic factor analysis. This retrospective study includes 150 patients who underwent a 2nd SCT for relapsed acute myeloblastic leukaemia (n = 61), acute lymphoblastic leukaemia (n = 47) or chronic myeloid leukaemia (n = 42) after a first allogeneic transplant (including 26 T-cell-depleted). The median interval between the first transplant and relapse, and between relapse and second transplant was 17 months and 5 months respectively. After the 2nd SCT, engraftment occurred in 93% of cases, 32% of patients developed acute graft-vs.-host disease (GVHD) >/= grade II and 38% chronic GVHD. The 5-year overall and disease-free survival were 32 +/- 8% and 30 +/- 8%, respectively, with a risk of relapse of 44 +/- 12% and a transplant-related mortality of 45 +/- 9%. In a multivariate analysis, five factors were associated with a better outcome after 2nd SCT: age < 16 years at second transplant; relapse occurring more than 12 months after the first transplant; transplantation from a female donor; absence of acute GVHD; and the occurrence of chronic GVHD. The best candidates for a second transplant are likely to be patients with acute leukaemia in remission before transplant, in whom the HLA-identical donor was female and who relapsed more than 1 year after the first transplant.     

Neuronally induced augmentation of cardiac output

OBJECTIVE: To determine whether cardiac output can be augmented by preferentially activating cardiac adrenergic efferent neurons. DESIGN: Elicited cardiac output responses were compared when cardiac myocytes were directly stimulated by a beta1-adrenoceptor agonist versus when they were indirectly influenced by beta2- adrenergic-sensitive cardiac efferent neurons. ANIMALS AND METHODS: The beta1-adrenoceptor agonist dobutamine or the selective beta2-adrenoceptor agonist terbutaline was continuously infused individually into the systemic circulation of 15 anesthetized pigs for 20 mins in 5 and 15 microgram/kg/min doses. Heart rate, left atrial chamber pressure, regional left ventricular intramyocardial systolic pressure, left ventricular chamber pressure and aortic pressure were monitored. Cardiac output was determined via the thermodilution technique before and at 10 min intervals during drug infusions. Ventricular tissues were removed thereafter and immediately frozen in liquid nitrogen for subsequent cardiac myocyte cell surface beta-adrenoceptor analysis. MAIN RESULTS: Both doses of terbutaline increased heart rate (approximately +18%) and cardiac output (approximately +20%). Heart rate (+12%) and cardiac output (+16%) increased when the high dose of dobutamine was tested. Left ventricular intramyocardial systolic pressure was increased by dobutamine (+15%) but not by terbutaline. Porcine ventricular cardiac myocytes primarily possess cell surface beta1-, rather than beta2-, adrenoceptors, making it unlikely that cardiac myocytes were directly affected by the doses of terbutaline tested. CONCLUSIONS: Beta2-adrenoceptor agonists enhance cardiac output primarily as a result of neuronally induced increases in heart rate in the porcine model. Adrenergic efferent neuronal enhancement of heart rate may be an effective way to increase cardiac output independently of directly augmented ventricular dynamics. Further study is required to determine whether the diseased myocardium can be supported by such neurocardiological means.     

Allogeneic stem cell transplantation with fludarabine-based, less intensive conditioning regimens as adoptive immunotherapy in advanced Hodgkin's disease

Six patients with advanced Hodgkin's disease in which multiple conventional treatments (median prior chemotherapy regimens: seven), radiation therapy, and a prior autologous stem cell transplantation (SCT) had failed underwent allogeneic SCT following a fludarabine-based conditioning regimen. Median age was 29 years (22-30). Median time to progression after autologous SCT was 6 months (4-21). Disease status at transplant was refractory relapse (n = 3) and sensitive relapse (n = 3). Cell source was filgrastim-mobilized peripheral blood stem cells from an HLA-identical sibling (n = 4) or matched unrelated donor marrow (n = 2). Conditioning regimens were fludarabine-cyclophosphamide-antithymocyte globulin (n = 4), fludarabine-melphalan (n = 1) and fludarabine-cytarabine-idarubicin (n = 1). Myeloid recovery was prompt, with an absolute neutrophil count > or =500/microl on day 12 (11-15). Median platelet recovery to > or =20000/microl was on day 9 (0-60). Chimerism studies on day 30 indicated 100% donor-derived hematopoiesis in 4/5 evaluable patients (4/4 non-progressors). All responders (3/3) have ongoing 100% donor-derived chimerism. Acute graft-versus-host disease (GVHD) was diagnosed in 4/6 evaluable patients. Chronic GVHD was present in 2/4 evaluable patients. There were no regimen-related deaths. Overall day 100 transplant-related mortality was 2/6 (33%). Three patients have expired and three are alive and progression-free with a median follow-up of 9 months (6-26) post transplant. We conclude that allogeneic stem cell transplantation with fludarabine-based preparative regimens is feasible in these high-risk, heavily pretreated HD patients.     

Densitometric analysis of beta 1- and beta 2-adrenoceptors in guinea-pig atrioventricular conducting system.

Quantitative autoradiography was used to determine the densities of beta 1- and beta 2-adrenoceptors in the atrioventricular conducting system in guinea-pig. (-)[125I]Cyanopindolol (CYP) was used to label beta 1- and beta 2-adrenoceptors in the absence or presence of the beta 1-adrenoceptor selective antagonist CGP 20712A (100 nM) or the beta 2-adrenoceptor selective antagonist ICI 118,551 (70 nM) or the non-selective beta-adrenoceptor antagonist (-)-propranolol (1 microM). Protein in discrete anatomical regions was determined using a densitometric method based on the dye Coomassie brilliant blue G. In the atrioventricular conducting system the proportion of beta 2-adrenoceptors determined by inhibition of total (-)[125I]-CYP binding by CGP 20712A (100 nM) ranged from 32.5% (atrioventricular node) to 48.7% (left bundle branch). In the atrioventricular node (16.8 fmol/mg protein), bundle of His (12.1 fmol/mg protein), right (17.4 fmol/mg protein) and left (21.1 fmol/mg protein) bundle branches and Purkinje cells there was a higher density of beta 2-adrenoceptors than in the interventricular septum (8.4 fmol/mg protein) and right atria (8.3 fmol/mg protein). The medial smooth muscle of the aorta, aortic valve, adventitia of the aorta, nerve tissue, tricuspid and mitral valves contained only beta 2-adrenoceptors. It is speculated that the use of beta-adrenoceptor antagonists to control cardiac arrhythmias involving a defect in conduction in the atrioventricular node should take into consideration both beta 1- and beta 2-adrenoceptors.     

New insights into beta2-adrenoceptor signaling in the adult rat heart

OBJECTIVE: The role of cAMP in beta(2)-adrenoceptor signaling and its functional relevance in adult rat heart has been the subject of considerable controversy. Therefore, we investigated the beta(2)-adrenoceptor pathways in both adult cardiomyocytes and in the intact hearts of Wistar rats with respect to protein kinase A (at Ser16)-, the key event in shortening of relaxation time, and CaM kinase II (at Thr17)-dependent phospholamban phosphorylation. METHODS: Contractile and cellular beta(1)/beta(2)-adrenergic responses were studied in parallel on the same perfused rat heart. (-)Isoproterenol and the beta(2)-adrenergic agonists zinterol and procaterol were used to discriminate the beta-adrenoceptor subtype-related actions. RESULTS: Beta(2)-adrenoceptor stimulation induces protein kinase A-dependent phospholamban phosphorylation in both adult cardiomyocytes and in adult hearts of rats. The beta(2)-adrenoceptor-mediated shortening of relaxation time in the heart correlates with Ser16 phosphorylation. Adenosine elicited antiadrenergic action on both beta(1)- and beta(2)-adrenergic signaling cascades by reducing the phosphorylation status of phospholamban. Only beta(1)-adrenoceptor stimulation produced significant CaM kinase II-related Thr17 phosphorylation, troponin I phosphorylation and activation of phosphorylase a. CONCLUSIONS: Our findings clearly show that beta(2)-adrenoceptor signaling is coupled to phospholamban phosphorylation and shortening of relaxation time in the adult rat heart.     

Influence of pre-existing donor atherosclerosis on the development of cardiac allograft vasculopathy and outcomes in heart transplant recipients.

OBJECTIVES: This study sought to evaluate the influence of donor lesions on the development of cardiac allograft vasculopathy and outcomes in heart transplant recipients. BACKGROUND: After orthotopic heart transplantation (OHT), coronary artery narrowing occurs as a combination of pre-existing donor lesions and new lesions that develop as a result of cardiac allograft vasculopathy. METHODS: Intravascular ultrasound (IVUS) studies were performed in 301 recipients at 1.3 +/- 0.6 months and again at 12.2 +/- 0.8 months after OHT. Additional IVUS studies were performed in 90 patients at two and three years of follow-up. Sites at baseline with maximum intimal thickness > or =0.5 mm were defined as pre-existing donor lesions. The angiographic diagnosis of transplant coronary artery disease (TCAD) was defined as a new > or =50% diameter narrowing of a major epicardial vessel. RESULTS: Donor lesions were present in 30% of the hearts. By IVUS, sites with donor lesions did not have a greater increase in intimal area compared with sites without donor lesions. Angiographically, the incidence of TCAD up to three years after transplantation was higher in recipients with donor lesions than in recipients without donor lesions (25% vs. 4%, p < 0.001). However, the three-year mortality rate was similar between recipients with or without donor lesions (4.5% vs. 5.2%, p = 1.0). CONCLUSIONS: Pre-existing donor lesions do not act as a nidus for accelerating the progression of intimal hyperplasia. However, patients with donor lesions have a higher incidence of angiographic TCAD. Donor lesions do not affect the long-term survival of patients with OHT up to three years.     

Effect of age on upregulation of the cardiac adrenergic beta receptors

Radioligand binding studies were performed to determine whether upregulation of postjunctional beta receptors occurs in sympathectomized hearts of aged animals. Fischer 344 rats 6, 12, and 24 months of age (n = 10) were used in these experiments. To produce sympathectomy, rats were injected with 6-hydroxydopamine hydrobromide (6-OHDA; 2 x 50 mg/kg iv) on days 1 and 8; the animals were decapitated on day 15. The depletion of norepinephrine in the heart was about 86% in each age group. 125I-Iodopindolol (IPIN), a beta adrenergic receptor antagonist, was employed to determine the affinity and total number of beta adrenergic receptors in the ventricles of the rat heart. The maximal number of binding sites (Bmax) was significantly elevated by 37%, 48%, and 50% in hearts from sympathectomized 6-, 12-, and 24-month-old rats, respectively. These results indicate that beta receptor mechanisms in older hearts can respond to procedures that cause upregulation of the beta adrenergic receptors.     

Agonist-induced desensitization of beta-adrenoceptor function in humans. Subtype-selective reduction in beta 1- or beta 2-adrenoceptor-mediated physiological effects by xamoterol or procaterol

We investigated the effects of beta 2- (procaterol 2 x 50 micrograms/day for 9 days) and beta 1- (xamoterol 2 x 200 mg/day for 14 days) adrenoceptor agonists on lymphocyte beta 2-adrenoceptor density and beta 1- and beta 2-adrenoceptor in vivo function (assessed as isoprenaline-infusion-evoked hemodynamic effects and exercise-induced tachycardia) in healthy volunteers. Procaterol decreased lymphocyte beta 2-adrenoceptor density and all beta 2-adrenoceptor-mediated in vivo effects but did not affect beta 1-adrenoceptor-mediated in vivo effects. In contrast, xamoterol neither affected lymphocyte beta 2-adrenoceptors nor beta 2-adrenoceptor-mediated in vivo effects but decreased beta 1-adrenoceptor-mediated in vivo effects. It is concluded that in humans, generally long-term application of beta 1- or beta 2-adrenoceptor agonists causes desensitization of beta-adrenoceptor function but in a beta-adrenoceptor subtype-selective fashion.     

Reversal of myocardial injury using genetically modulated human skeletal myoblasts in a rodent cryoinjured heart model

BACKGROUND: We hypothesized that combination therapy using human myoblasts and VEGF165 will lead to better prognosis in a failing heart. METHODS: Forty-eight female Wistar rats with cryoinjured hearts were randomized into non-treated normal (group-1, n=12), DMEM injected (group-2, n=10), myoblast-transplanted (group-3, n=12) and myoblast-hVEGF(165) (group-4, n=14). Ten days after cryoinjury, 200 microl DMEM containing 3x10(6) cells or without cells was injected into the injured myocardium. Animals were maintained on cyclosporine for 6 weeks post cell transplantation. Heart function was assessed by echocardiography. Animals were sacrificed and hearts were processed for histochemical and immunohistochemical studies. RESULTS: Histological examination showed survival of the donor myoblasts expressing lac-z and hVEGF165 in rat cardiac tissue. Fluorescent immunostaining for vWillebrand Factor-VIII and smooth muscle actin expression at low power microscope (x100) showed significantly higher blood vessel density in group-4 (31.25+/-1.82; 24.63+/-0.92) as compared to group-2 (13.29+/-1.0; p<0.001; 9.71+/-0.81, p<0.001) and group-3 (16.50+/-1.43, p<0.001; 14.5+/-1.34, p<0.001). Echocardiography showed that ejection fraction and fractional shortening of group-3 (93.36+/-1.52%, p=0.005; 75+/-3.75%, p=0.024) and group-4 (94.8+/-1.62%, p=0.003; 76.13+/-2.15%, p=0.011) significantly improved as compared to group-2 (81.8+/-3.3%, 55.1+/-7.18%). CONCLUSION: Myoblasts carrying of hVEGF165 are potential therapeutic transgene carriers for cardiac repair.     

Reduced beta 2-adrenoceptor responsiveness in exercise-induced asthma

Beta-adrenoceptor responsiveness was studied both in vivo and in vitro in patients with exercise-induced asthma (EIA), asthmatic patients without EIA (NEIA), and control subjects. All subjects were age- and sex-matched and without medication at least one week prior to the tests. In vivo, beta-adrenoceptor responsiveness was evaluated by plasma concentration-effect studies for intravenously infused isoprenaline (0.02-0.1 micrograms X kg-1 X min-1). Mainly beta 2-adrenoceptor mediated responses to isoprenaline, ie, decreases in diastolic blood pressure and increases in plasma cyclic AMP, were reduced in EIA patients but not in NEIA patients. Heart rate and plasma glycerol responses to isoprenaline did not differ between the groups. In vitro, the beta 2-adrenoceptor mediated accumulation of cyclic AMP in lymphocytes stimulated by isoprenaline was attenuated (p less than 0.05) in EIA patients, whereas the beta 2-adrenoceptor responsiveness of lymphocytes from NEIA patients was normal. Thus, beta 2-adrenoceptor mediated responses were reduced both in vivo and in vitro in EIA patients, but not in NEIA patients. This finding that beta 2-adrenoceptor responsiveness was reduced only in a subgroup of asthmatic patients could explain some of the controversies in the literature concerning beta-adrenoceptor function in asthma.