Number Of Β-adrenergic Receptors Research Articles

Effect of physical training on ventricular β-adrenergic receptor adenylate cyclase system of diabetic rats

This study was designed to assess the effect of physical training on the ventricular β-adrenergic receptor adenylate cyclase system of diabetic rats. Mild diabetes mellitus was induced by an intravenous (IV) injection of streptozotocin (45 mg/kg). Rats were randomized into a group submitted to a progressive 10-week running program on a treadmill, while another group was kept sedentary. A group of sedentary nondiabetic rats was used as normal controls. Results showed a similar reduction in the density of β-adrenergic receptors in sedentary diabetic ( P < .05) and trained diabetic rats ( P < .01) compared with controls, without any significant alteration in the dissociation constant. The basal and the sodium fluoride-stimulated maximal adenylate cyclase activities were similar in the three groups. However, the maximal response of adenylate cyclase to isoproterenol was significantly reduced in the two diabetic groups compared with controls ( P < .01). The decrease in adenylate cyclase response to isoproterenol observed in the diabetic groups appeared to be associated with a reduction in the total number of β-adrenergic receptors and more specifically in those existing in the high-affinity state. On the other hand, the hyperglycemia and hyperglucagonemia present in sedentary diabetic rats was improved by training. These data suggest that the beneficial effects observed in response to training in experimental diabetes are not associated with changes in β-adrenergic receptor adenylate cyclase system on membranes from ventricular tissue.

β-Adrenergic receptor binding in frontal cortex of suicide victims

The high-affinity binding of the β-adrenergic receptor antagonist, [ 3H]dihydroalprenolol, was measured in homogenates of frontal cortex (Brodmann's areas 8 and 9) of suicide victims and matched controls. Suicides were classified as violent if gunshot, hanging, or jumping was the cause of death and as nonviolent if carbon monoxide poisoning or drug overdose was the cause of death. No significant differences were found between controls and nonviolent or violent suicide victims with regard to the number of β-adrenergic receptors ( B max), or the binding affinity ( K d) of the receptor. β-Adrenergic receptor binding was not significantly affected by sex, age, race, or postmortem interval. Serotonin-2 receptor binding ( B max) in homogenates from the same tissue specimens was previously reported to be significantly increased in violent suicides (Arora and Meltzer 1989). In these sample groups, suicide by violent means appears to be associated with an increase in the number of serotonin-2, but not β-adrenergic, receptors in frontal cortex.

Differences in the accessibility of the β-adrenergic receptor in isolated hepatocytes from foetal and adult rats

β-receptor number (measured by [ 3H]-CGP 12 177 binding) and β-adrenergic response (measured by isoproterenol stimulated glucose liberation and isoproterenol stimulated adenylate cyclase activity) were compared in hepatocytes isolated from foetal (on day 22 of gestation), adult female and adult male rats. β-receptor numbers in crude membrane preparations of hepatocytes from adult female and adult male rats were found to be nearly equal (15.5 and 15.1 fmol/mg), but in crude membrane preparations of foetal rats β-adrenergic receptor number was significantly higher (34.3 fmol/mg). Determination of number of β-adrenergic surface receptors of intact hepatocytes showed relative high values in foetal rats (about 22,000/cell) and adult female rats (about 20,000/cell), but in male rats the number was less (about 6500/cell). Glucose liberation was stimulated by isoproterenol to the same extent in hepatocytes isolated from adult female and foetal rats (about 150% over basal), whereas no effect was found in hepatocytes isolated from adult male rats. Dose-response curves showed that in foetal rat hepatocytes glucose release was already increased by 10 −8 M isoproterenol, whereas in female rat hepatocytes at least 10 −6 M isoproterenol was required. Adenylate cyclase was stimulated by isoproterenol in lysates of hepatocytes from adult female rats by about 180% and from foetal rats by about 250%. No effects were observed using lysates of hepatocytes from adult male rats. We interpret the observed differences of β-adrenergic responses between adult female and male rats as being primarily caused by different accessibility of the β-receptor to the β-agonist isoproterenol in intact hepatocytes. There are no differences in the number of accessible β-adrenergic cell surface receptors in foetal and female rats, but the surface receptor density is significantly higher in foetal rats.

Effects of metoprolol on rest and exercise cardiac function and plasma catecholamines in chronic congestive heart failure secondary to ischemic or idiopathic cardiomyopathy

To define the effects of 2 months of metoprolol therapy on cardiac function, aerobic performance and sympathetic nervous system activity, metoprolol (75 to 100 mg/day) was administered to 10 patients with chronic congestive heart failure (CHF). Metoprolol was discontinued in 2 patients because of worsening CHF. In the remaining 8 patients, peak oxygen uptake increased significantly (14.8 ± 3.0 to 16.1 ± 2.5 ml/kg/min, p < 0.05) as did the oxygen pulse (9.0 ± 2.2 to 12.6 ±1.8 ml/beat, p < 0.02). Resting heart rate (87 ± 18 to 62 ± 9 beats/min, p < 0.05) and peak exercise heart rate (133 ± 13 to 105 ± 30 beats/min, p < 0.02) were both reduced. Mean resting ejection fraction increased from 0.15 ± 0.06 to 0.25 ± 0.11 and peak exercise ejection fraction also tended to increase (0.19 ± 0.11 to 0.28 ± 0.15, difference not significant). Both resting plasma norepinephrine (613 ± 706 to 303 ± 142 pg/ml, p < 0.05) and epinephrine (71 ± 50 to 40 ± 21 pg/ml, p < 0.05) were reduced. Circulating lymphocyte β-adrenergic receptor number was unchanged (1,334 ± 292 to 1,344 ± 456 receptors/cell, difference not significant). It is concluded that metoprolol therapy is associated with improvements in rest and exercise ventricular performance and maximal aerobic capacity. These improvements are associated with a decline in resting sympathetic nervous system activity.

Testosterone treatment of ovariectomized rats: Effects on lipolysis regulation in adipocytes

The effects of testosterone treatment (2 mg every 14 days, for three months) on adipocyte lipolysis of intact (250-300 g body weight) and ovariectomized female rats were studied. Testosterone treatment of intact rats had no effect. Ovariectomy was followed by an increase in fat cell size and a decrease of lipolysis stimulated by isoproterenol, norepinephrine, epinephrine, forskolin, cAMP and isobutylmethylxantine. The number of beta-adrenergic receptors was reduced. There was, however, no change in the antilipolytic effects of UK 14,304 (alpha 2-adrenergic agonist), nicotinic acid, N6-phenylisopropyladenosine or insulin. Testosterone treatment of ovariectomized rats restored the number of beta-adrenoceptors and lipolysis stimulated by cAMP and isobutylmethylxantine, but not lipolysis stimulated by catecholamines and forskolin, suggesting a remaining defect in the catalytic unit of adenylate cyclase. These results indicate that ovariectomy is followed by a profound derangement of the lipolytic pathway at several levels, from beta-adrenoceptors number to the triglyceride lipase activity. This is partially restored by treatment with testosterone, which, however, has no effect on intact female rats. This study emphasizes the importance of ovarian integrity for the lipolytic regulation and the inability of testosterone to replace ovarian function in this regard or to affect lipolysis in intact female rats.

Effects of growth hormone on the β-adrenergic receptor number of rat adipocyte membranes

Effects of growth hormone on the β-adrenergic receptor number of rat adipocyte membranes

Decreased β-adrenergic responses of rat small intestine due to non-insulin-dependent diabetes

Relaxing responses to salbutamol of duodenum, jejunum and ileum isolated from alloxan-induced non-insulin-dependent diabetic rats were investigated by means of pharmacodynamic analysis using pD 2 (apparent receptor affinity) and α E (intrinsic activity) values. β-Adrenergic responses of these three intestinal parts of diabetic rats were found to be significantly decreased when compared to controls. The decreased responses may be attributable to a decrease in the number of β-adrenergic receptors. The gastro-intestinal manifestations reported in diabetic patients are possibly linked to the occurrence of a decrease in β-adrenergic receptors. Furthermore, this model seems to be useful for the investigations of gastro-intestinal complications resulting from non-insulin-dependent diabetes.

The influence of hypoxia on p-adrenergic receptors and their intracellular coupling in isolated adult canine myocytes

The response of β-adrenergic receptors and their coupling to intracellular events during hypoxia was evaluated in isolated, intact adult canine ventricular myocytes. Myocytes exposed to 10 minutes of hypoxia (PO2, <15 mm Hg) at 37°C exhibited no change in β-adrenergic receptor number or affinity. Even longer intervals of hypoxia (30 and 60 minutes) did not result in any significant changes in β-adrenergic receptor number. However, after 120 minutes of hypoxia, the apparent β-adrenergic receptor number increased markedly. This increase in measured β-adrenergic receptor number was shown when more than 95% of the myocytes were irreversibly injured as assessed by light microscopy, electron microscopy, and release of intracellular enzymes. Although basal levels of cyclic AMP remained unchanged during normoxia and hypoxia, cyclic AMP levels stimulated by isoproterenol (10-5 M) were significantly decreased after 60 and 120 minutes of hypoxia. Furthermore, prolonged hypoxia produced a marked downward and rightward shift in the isoproterenol-stimulated cyclic AMP response curve. Enhanced cyclic AMP levels were produced and maintained by forskolin (10-4 M) stimulation in normoxic and hypoxic myocytes. These findings demonstrate that reversible hypoxic damage does not result in significant β-adrenergic receptor alterations, thus, precluding a significant contribution of increased β-adrenergic receptor density to arrhythmogenic mechanisms during early ischemia. Protracted periods of hypoxia increase the measurable number of β-adrenergic receptors only when the cells have undergone irreversible damage. The data demonstrate that the apparent increase in receptor number in damaged cells is also associated with uncoupling of the β-adrenergic receptor to production of cyclic AMP

β-Adrenergic receptor binding in brain of alcoholics

The binding of agonists and antagonists to β-adrenergic receptors in brain tissue obtained postmortem in nonalcoholic controls and matched intoxicated and sober alcoholics was measured to assess the state of the receptors and their coupling to adenylate cyclase. Binding of antagonist, iodocyanopindolol, to cerebral cortical and cerebellar membrane preparations was not different in alcoholics compared to that in controls, suggesting that the number of β-adrenergic receptors was not affected by chronic ethanol ingestion. Agonist binding data, however, indicated the loss of the high-affinity agonist binding state of the β-adrenergic receptor, representing the receptor-guanine nucleotide binding protein (G s) complex. Such changes were observed in cerebral cortex but not in cerebellum of intoxicated alcoholics. These data suggest that cerebral cortical β-adrenergic receptors are uncoupled from adenylate cyclase in these subjects. In cerebral cortical and cerebellar membranes of sober alcoholics both the high- and low-affinity agonist binding sites were observed. These findings are similar to those seen in animal studies and suggest that the effect of chronic ethanol ingestion on β-adrenergic receptor-adenylate cyclase coupling is brain region specific and reversible with abstinence. Ethanol-induced changes in the coupling of receptors to adenylate cyclase may contribute to the physiological and behavioral manifestations of alcohol abuse.

Use of N-ethylmaleimide to directly determine the proportion of β-adrenergic receptors exhibiting high affinity for agonists on human mononuclear leukocyte membranes

Following incubation with the β-adrenergic agonist isoproterenol (ISO) and the alkylating agent N-ethylmaleimide (NEM), the number of β-adrenergic receptors measured on human mononuclear leukocyte (MNL) membranes decreased. Pretreatment induced an approximately 40% loss of measurable receptors. The proportion of receptors lost was that which formed the ternary complex of agonist-receptor-G s protein (H-R-G s) and exhibited high affinity for agonists. In comparison studies, the loss of receptors was found to be similar to the proportion of receptors that form the high affinity state of the receptor (% R H ) for agonist in agonist competition binding studies. Acute exposure to agonist induced a similar reduction in ISO/NEM “sensitive” receptors and the % R H . These experiments indicate that pretreatment of MNL membranes with ISO/NEM is a powerful tool with which to directly determine the percentage of receptors able to form an agonist high affinity state.

Electrophysiological responsiveness to isoproterenol in rat hippocampal slices correlates with changes in β-adrenergic receptor density induced by chronic morphine treatment

The effects of chronic morphine treatment and morphine withdrawal on β-adrenergic receptor density and electrophysiological responsiveness in rat hippocampus were examined. Chronic treatment of rats with morphine for 14 days resulted in a 19% increase in the number of β-adrenergic receptors in hippocampus, as measured by the binding of the specific antagonist [ 3H]dihydroalprenolol (DHA). In comparison, the number of specific binding sites for [ 3H]DHA was decreased 27% in hippocampus in morphine-withdrawn animals, compared to saline-treated controls. These alterations in β-adrenergic receptor density were not accompanied by a significant change in the dissociation constant ( K d) for [ 3H]DHA or in the inhibitory constants ( K i) for the displacement of the [ 3H]-antagonist by either norepinephrine or isoproterenol. Electrophysiological experiments in the in vitro hippocampal slice preparation revealed that responses to threshold as well as maximal concentrations of isoproterenol were significantly enhanced in morphine-dependent animals, compared to controls, whereas electrophysiological responsiveness to maximal concentrations of isoproterenol was decreased in slices from morphine-withdrawn rats. The results of this study indicate that β-adrenergic receptors in hippocampus are up-regulated during the development of morphine dependence and down-regulated during opiate withdrawal. These changes in hippocampal β-adrenergic receptor density are likely to be of functional relevance since they are manifested in a corresponding increase and decrease, respectively, in electrophysiological responsiveness to an exogenously administered β-adrenergic receptor agonist.

Reduced Number of β-Adrenergic Receptors in the Myocardium of M-SHRSP

Reduced Number of β-Adrenergic Receptors in the Myocardium of M-SHRSP

O-313 - Reduced number of β-adrenergic receptors in the myocardium of malignant stroke-prone spontaneously hypertensive rats (M-SHRSP)

O-313 - Reduced number of β-adrenergic receptors in the myocardium of malignant stroke-prone spontaneously hypertensive rats (M-SHRSP)

Norepinephrine and serotonin content of the murine spleen: Its relationship to lymphocyte β-adrenergic receptor density and the humoral immune response in vivo and in vitro

Numerous reports in the literature describe the effects of β-adrenergic agonists and/or their second messenger cyclic AMP on in vitro and in vivo immune responses. The fact that the murine spleen receives rich adrenergic innervation and that the pharmacologic disruption of this innervation leads to altered immune responsiveness has led some investigators to postulate that the immune system may be modulated in vivo by the sympathetic nervous system. In this report HPLC is used to quantitate the norepinephrine (NE) and serotonin (5-HT) found in the B6C3F1 spleen. These transmitters were found to be distributed nonhomogeneously among the cell, supernatant, and capsule fractions of the spleen. The majority of NE was found in the capsule while most 5-HT was found associated with the cell pellet. During an immune response to sheep red blood cells the concentration of NE in the spleen was found to be decreased. However, the total amount of splenic NE was unaltered and thus the decreased concentration may be attributed to the increased weight of immunized spleens. Simultaneously, the total amount of the dopamine metabolite 3,4-dihydroxyphenylacetic acid found in the spleen was found to be increased, a difference not explained by increased spleen size. These results suggest an antigen-induced increase in sympathetic activity in the spleen. Splenic NE could be rapidly depleted using 6-hydroxydopamine. Lymphocytes from the NE-depleted animals were found to have upregulated the number of β-adrenergic receptors on their surfaces and demonstrated a reduced ability to respond to sheep red blood cells in vitro.

Deficiency of cardiac beta-adrenergic receptor in streptozocin-induced diabetic rats.

The number of beta-adrenergic receptors in cardiac myocytes isolated from rats made diabetic with streptozocin (STZ) for 10 wk was measured by use of a hydrophilic nonselective antagonist [3H]CGP 12177 and was found to decrease to 59% of the number in control rats (P less than .05), without any change in affinity. Similarly, using [125I]iodocyanopindolol as a ligand, we found a decrease in the beta-adrenergic-receptor number on cardiac plasma membrane isolated from the diabetic rats [29% decrease (P less than .05) at 1 wk, 50% (P less than .01) at 3 wk, and 49% (P less than .01) at 10 wk compared with control rats]. However, the serum triiodothyronine level that had been known to modulate the beta-adrenergic-receptor-adenylate cyclase system was decreased in the 1-wk-diabetic rats but not in the 10-wk-diabetic rats compared with each control group. Furthermore, there was no difference in urinary catecholamine excretion between diabetic and control groups. In the 10-wk-diabetic rats, the response of adenylate cyclase to isoproterenol was significantly defective (56% decrease compared with control rats; P less than .05), although both the basal and the forskolin-stimulated maximum adenylate cyclase activities and a half-maximum concentration of isoproterenol for the stimulation of adenylate cyclase were similar in control and diabetic rats. On the other hand, both cholera toxin-dependent and islet-activating protein-dependent [32P]NAD incorporations into cardiac plasma membrane were markedly increased in the diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Independent activation of adenylate cyclase by erythropoietin and isoprenaline

The possibility that catecholamines modulate the erythropoietin-induced increase in production of cyclic AMP was investigated by examining the effect of erythropoietin and/or l-isoprenaline on the activity of the plasma membrane adenylate cyclase of anaemic rabbit bone marrow erythroblasts. Membranes isolated from cells cultured in the presence of both hormones exhibited both the transient stimulation of basal activity characteristic of erythropoietin action and the loss of the in vitro response to l-isoprenaline, concomitant with the loss of β-adrenergic receptors, characteristic of l-isoprenaline stimulation. The presence of erythropoietin during cell culture with L-isoprenaline had no effect on the desensitization or number of β-adrenergic receptors. The stimulation of adenylate cyclase by erythropoietin was observed also in the presence of the β-antagonist propranolol, when both were added either to whole cells or to isolated membranes. We conclude that these two hormones activate adenylate cyclase independently of each other, via different receptors, with little evidence of cross-modulation.

A quenched-flow study of a receptor-triggered second messenger response: Cyclic AMP burst elicited by isoproterenol in C6 glioma cell membranes

Fast kinetic studies of cAMP accumulation in C6 cell membranes show a burst of cAMP after β-adrenergic receptor stimulation by isoproterenol. This burst is no longer observed when the ATP present in membrane preparations is hydrolyzed, but can be restored by their preincubation in the presence of ATP-Mg. The size of the burst is much larger than the number of β-adrenergic receptors and is of the same order of magnitude as the value reported for G proteins. Further characterization of the burst will allow studies of the functional interaction of receptor-adenylate cyclase components in C6 membranes.

β-Adrenergic Receptors in Ischemic and Nonischemic Canine Myocardium: Relation to Ventricular Fibrillation and Effects of Pretreatment with Propranolol and Hexamethonium

To explore possible roles of the sympathetic nervous system (especially the beta-adrenergic receptor and cAMP system) in the pathogenesis of ventricular fibrillation (VF), the authors examined changes in the number of myocardial beta-adrenergic receptors and the cAMP level in animals showing VF after experimental induction of myocardial ischemia. In animals that developed VF approximately 15 min after coronary ligation, the ischemic myocardium had a significantly larger number of beta-adrenergic receptors (90 +/- 8 fmol/mg protein) and a significantly higher level of cAMP (1.4 +/- 0.17 nmol/g weight) compared with the nonischemic area where the number of beta-receptors was 68 +/- 7 fmol/mg protein and the cAMP level was 0.80 +/- 0.20 nmol/g weight. In animals in which VF was electrically induced 20 min after coronary ligation, no elevation was recorded in the ischemic area in terms of the number of beta-adrenergic receptors (49 +/- 6 fmol/mg protein) and the level of cAMP (0.79 +/- 0.06 nmol/g weight). When animals were pretreated with a beta-blocker or a ganglion blocker, coronary ligation did not result in VF. In the ischemic area of these animals, no significant change was noted in the number of beta-adrenergic receptors (54 +/- 7 fmol/mg protein for animals pretreated with a beta-blocker, 56 +/- 3 fmol/mg protein for animals pretreated with a ganglion blocker). These results suggest that there is a strong correlation between the pathogenesis of VF (observed about 15 min after coronary ligation) and the increase of the number of beta-adrenergic receptors and cAMP levels.

Reduced Number of β-Adrenergic Receptors in the Myocardium of MSHRSP

Reduced Number of β-Adrenergic Receptors in the Myocardium of MSHRSP

The interaction of dietary fatty acid and cholesterol on catecholamine-stimulated adenylate cyclase activity in the rat heart

Diets supplemented with high levels of saturated or unsaturated fatty acids supplied by addition of sheep kidney fat or sunflower seed oil, respectively, were fed to rats with or without dietary cholesterol. The effects of these diets on cardiac membrane lipid composition, catecholamine-stimulated adenylate cyclase and β-adrenergic receptor activity associated with cardiac membranes, were determined. The fatty acid-supplemented diets, either with or without cholesterol, resulted in alterations in the proportion of the ( n − 6) to ( n − 3) series of unsaturated fatty acids, with the sunflower seed oil increasing and the sheep kidney fat decreasing this ratio, but did not by themselves significantly alter the ratio of saturated to unsaturated fatty acids. However, cholesterol supplementation resulted in a decrease in the proportion of saturated and polyunsaturated fatty acids and a dramatic increase in oleic acid in cardiac membrane phospholipids irrespective of the nature of the dietary fatty acid supplement. The cholesterol/phospholipid ratio of cardiac membrane lipids was also markedly increased with dietary cholesterol supplementation. Although relatively unaffected by the nature of the dietary fatty acid supplement, catecholamine-stimulated adenylate cyclase activity was significantly increased with dietary cholesterol supplementation and was positively correlated with the value of the membrane cholesterol/phospholipid ratio. Although the dissociation constant for the β-adrenergic receptor, determined by [ 125I](−)-iodocyanopindolol binding, was unaffected by the nature of the dietary lipid supplement, the number of β-adrenergic receptors was dramatically reduced by dietary cholesterol and negatively correlated with the value of the membrane cholesterol/phospholipid ratio. These results indicate that the activity of the membrane-associated β-adrenergic/adenylate cyclase system of the heart can be influenced by dietary lipids particularly those altering the membrane cholesterol/phospholipid ratio and presumably membrane physico-chemical properties. In the face of these dietary-induced changes, a degree of homeostasis was apparent both with regard to membrane fatty acid composition in response to an altered membrane cholesterol/phospholipid ratio, and to down regulation of the β-adrenergic receptor in response to enhanced catecholamine-stimulated adenylate cyclase activity.