Β-adrenergic Receptor Binding Research Articles

Distribution and properties of cardiac and pulmonary β-adrenergic receptors in corn snakes (Pantherophis guttatus) and Boa constrictor (Boa constrictor)

The aim of the present study was to characterize β-adrenergic receptors in the snake heart and lung of corn and Boa constrictor snakes. The β-adrenergic receptor binding sites were studied in purified heart and lung membranes using the specific β-adrenergic receptor antagonist [125J]-iodocyanopindolol (ICYP) and subtypes using selective β1-adrenergic receptor antagonist CGP-20712A and selective β2-adrenergic receptor antagonist ICI-118.551. A saturable and specific β-adrenergic receptor binding site was detected in cardiac membranes with maximal receptor density (Bmax) of 43.99 ± 3.86 fmol/mg protein (corn snake) and 58.07 ± 2.88 fmol/mg protein (Boa constrictor) as well as KD of 24.21 ± 7.38 pM (corn snake) and 21.48 ± 3.85 pM (Boa constrictor) and in lung membranes (Bmax fmol/mg protein: 55.95 ± 16.28 (corn snake) and 107.00 ± 14.21 (Boa constrictor); KD pM: 71.25 ± 21.92 (corn snake) and 55.04 ± 18.68 (Boa constrictor)). Competition-binding studies showed β-adrenergic receptors with low affinities to the β2-selective adrenergic receptor antagonist and high affinity binding to β1-selective adrenergic receptor antagonist in both heart and lung tissues of both snake species, suggesting the presence of high population of the post-synaptic β1-adrenergic receptor subtype. It seems that the presence of the predominant β1-subtype also in lung tissues may indicate the importance of the vascular system in the snake lung.

Cardiac hyporesponsiveness in severe sepsis is associated with nitric oxide-dependent activation of G protein receptor kinase.

G protein-coupled receptor kinase isoform 2 (GRK2) has a critical role in physiological and pharmacological responses to endogenous and exogenous substances. Sepsis causes an important cardiovascular dysfunction in which nitric oxide (NO) has a relevant role. The present study aimed to assess the putative effect of inducible NO synthase (NOS2)-derived NO on the activity of GRK2 in the context of septic cardiac dysfunction. C57BL/6 mice were submitted to severe septic injury by cecal ligation and puncture (CLP). Heart function was assessed by isolated and perfused heart, echocardiography, and β-adrenergic receptor binding. GRK2 was determined by immunofluorescence and Western blot analysis in the heart and isolated cardiac myocytes. Sepsis increased NOS2 expression in the heart, increased plasma nitrite + nitrate levels, and reduced isoproterenol-induced isolated ventricle contraction, whole heart tension development, and β-adrenergic receptor density. Treatment with 1400W or with GRK2 inhibitor prevented CLP-induced cardiac hyporesponsiveness 12 and 24 h after CLP. Increased labeling of total and phosphorylated GRK2 was detected in hearts after CLP. With treatment of 1400W or in hearts taken from septic NOS2 knockout mice, the activation of GRK2 was reduced. 1400W or GRK2 inhibitor reduced mortality, improved echocardiographic cardiac parameters, and prevented organ damage. Therefore, during sepsis, NOS2-derived NO increases GRK2, which leads to a reduction in β-adrenergic receptor density, contributing to the heart dysfunction. Isolated cardiac myocyte data indicate that NO acts through the soluble guanylyl cyclase/cGMP/PKG pathway. GRK2 inhibition may be a potential therapeutic target in sepsis-induced cardiac dysfunction.NEW & NOTEWORTHY The main novelty presented here is to show that septic shock induces cardiac hyporesponsiveness to isoproterenol by a mechanism dependent on nitric oxide and mediated by G protein-coupled receptor kinase isoform 2. Therefore, G protein-coupled receptor kinase isoform 2 inhibition may be a potential therapeutic target in sepsis-induced cardiac dysfunction.

Effects of dexamethasone and colostrum feeding on mRNA levels and binding capacities of β-adrenergic receptors in the liver of neonatal calves

Glucocorticoids increase plasma glucose concentrations in neonatal calves, but not hepatic gluconeogenic enzyme mRNA levels and activities. Catecholamines, too, enhance plasma glucose levels and regulate hepatic glucose metabolism. We have measured hepatic mRNA levels of β-adrenergic receptors and β-adrenergic receptor binding in neonatal calves on day 5 of life. Calves were fed either colostrums (C) or an isoenergetic milk-based formula (F), and in each feeding group, half of the calves were treated with dexamethasone (DEXA; 30 μg/(kg body weight day)). Abundance of mRNA was highest ( P < 0.01) for β 2-adrenergic receptors and was higher ( P < 0.01) for β 1- than for β 3-adrenergic receptors. DEXA treatment decreased ( P < 0.05) β 1- and β 2-adrenergic receptor mRNA levels. β 3-Adrenergic receptor mRNA levels were higher ( P < 0.05) in colostrum- than in formula-fed calves. Competitive binding revealed highest affinities for alprenolol, propranolol (both β 1- and β 2-antagonists), and ICI-188,551 (β 2-antagonist), which did not significantly differ from each other. Atenolol (β 1-antagonist) up to 10 −5 M did not displace ( 3H)-CGP-12177 from receptors. Competitive binding for adrenaline was best fitted by a two-receptor model. DEXA decreased ( P < 0.05) ( 3H)-CGP-12177 binding capacities, whereas binding affinity of ( 3H)-CGP-12177 was not affected by DEXA or different feeding. Binding sites correlated positively with mRNA levels of β 2-adrenergic receptors ( r = 0.56; P < 0.01). In conclusion, β 2-adrenergic receptors were the dominant subtype in the hepatic tissue. Feeding did not significantly affect β 2-adrenergic binding sites. However, DEXA decreased β 2-adrenergic binding sites and this was regulated at the transcriptional level.

A study on nitric oxide, β-adrenergic receptors and antioxidant status in the polymorphonuclear leukocytes from the patients of depression

Background: alterations in the polymorphonuclear leukocyte (PMNs) receptors, second messenger system and in their responses have been found associated with depression. Recently role of tetrahydrobiopterin and nitric oxide has also been reported in the depressive disorders. It was therefore considered worthwhile to investigate the NOS activity in the PMNs, which like neurons, also express neuronal NOS (nNOS), antioxidant enzyme levels [superoxide dismutase (SOD), catalase and glutathione peroxidase (Gpx)] and β-adrenergic receptors in the patients of depression. Methods: patients were diagnosed according to the DSM-IV and were medication free, while healthy age-matched controls were also included in the study to estimate nitrite content, β-adrenergic receptors and antioxidant enzymes in the PMNs according to the standard methodologies. Results: an analysis of 66 cases of depression and 114 controls revealed 73% decrease in nitrite content and 71% decrease in β-adrenergic receptor binding in the patients as compared to the healthy controls. However, activities of SOD, catalase and Gpx were not significantly altered in the patients. Conclusion: the results of the present study for the first time indicate alterations the NOS activity in PMNs obtained form the patients of affective disorders.

Adolescent nicotine exposure alters cardiac autonomic responsiveness: β-adrenergic and m2-muscarinic receptors and their linkage to adenylyl cyclase

Recent work indicates that adolescent smokers have an abnormally high incidence of heart rate irregularities. In the current study, adolescent rats received nicotine by continuous infusion from postnatal days (PN) 30–47.5, using a regimen designed to produce plasma levels found in smokers. We then assessed the levels of cardiac β-adrenergic and m2-muscarinic cholinergic receptor binding, and receptor linkages to adenylyl cyclase activity, during nicotine exposure and for 1 month afterwards. In the nicotine-exposed group, m2-receptors showed a significant reduction that persisted through PN75, 1 month after the termination of treatment. β-Receptors showed a tendency toward initial suppression and subsequent elevation. The receptor changes were accompanied by corresponding alterations in the response of adenylyl cyclase to carbachol and isoproterenol: the inhibitory muscarinic response was reduced, so that the net response to combined treatment with carbachol and isoproterenol was enhanced. There were additional changes in basal and forskolin–Mn 2+-stimulated adenylyl cyclase activity suggestive of shifts in enzymatic catalytic properties. The effects of adolescent nicotine exposure were distinct from those seen previously with fetal nicotine treatment. In light of the worldwide increase in tobacco use by teenagers, these studies raise concern that cardiovascular function may be especially vulnerable during this critical period.

Neonatal STZ model of type II diabetes mellitus in the Fischer 344 rat: characteristics and assessment of the status of the hepatic adrenergic receptors

The Fischer 344 rat was found to be extremely sensitive to the diabetogenic effects of neonatally injected streptozotocin (STZ): injection of 40–100 mg/kg STZ at 1.5 days postnatal produced in the adult graded levels of hyperglycemia in males but not the females. The optimal dose in the 1.5 day old male was 80 mg/kg: it produced hyperglycemia without affecting growth or thyroid status in the adult. The neonatally STZ-injected adult rat displayed characteristics consistent with type II diabetes: mild hyperglycemia accentuated by fasting or consumption of a high fat diet; little change in insulin levels; slight elevation in glucagon levels; no alterations in ketones. Using radioligand binding techniques to isolated rat liver plasma membranes, compared to the control state, the type II diabetic state was found to have: no effect on either α 2- or β-adrenergic receptor binding; a decrease in the major dominant α 1-adrenergic receptor, reflecting a decrease in receptor numbers but not their affinity; an increase in the plasma membrane calcium transport system, potentially depleting intracellular calcium stores essential for producing an α 1-adrenergic receptor response. Since the α 1-adrenergic receptor–calcium effector system is critical for the actions of catecholamines in the rat, these results suggest that the liver in the type II diabetic state may be refractory to the actions of catecholamines. We propose that the diabetes-evoked decrease in the dominant adrenergic receptor–effector system through which catecholamines act may be the cellular expression of defective glucocounterregulation in the diabetic state.

Specific elevation of transcript levels of particular protein subtypes induced in brown adipose tissue by cold exposure

To understand the difference in metabolic flow in rat brown adipose tissue (BAT) from that in white adipose tissue (WAT) at the molecular level, we examined the steady-state transcript levels of 39 proteins in both adipose tissues with and without cold exposure by Northern blot analysis. In addition to the transcript levels of uncoupling protein isoforms, those of proteins involved in the transport and catabolism of fatty acids and glucose in BAT were elevated by cold exposure, suggesting the stimulation of utilization of fatty acids and glucose as fuels in BAT. As to these changes, the muscle-type subtypes were remarkable; and therefore, they were suggested to be responsible for the cold exposure-induced acceleration of energy expenditure in BAT. Furthermore, of the isoforms of β-adrenergic receptor (β-AR) and CCAAT enhancer binding protein (C/EBP), transcript levels of β 1-AR and C/EBPβ in BAT were increased by the cold exposure. Possible roles of these proteins in energy metabolism in BAT were discussed.

Modulation of mouse cardiac function in vivo by eNOS and ANP.

To study the role of endothelial nitric oxide synthase (eNOS) in cardiac function, we compared eNOS expression, contractility, and relaxation in the left ventricles of wild-type and eNOS-deficient mice. eNOS immunostaining is localized to the macro- and microvascular endothelium throughout the myocardium in wild-type mice and is absent in eNOS-/- mice. Whereas blood pressure is elevated in eNOS-/- mice, baseline cardiac contractility (dP/dt(max)) is similar in wild-type and eNOS-/- mice (9,673 +/- 2, 447 and 9,928 +/- 1,566 mmHg/s, respectively). The beta-adrenergic agonist isoproterenol (Iso) at doses of >/=1 ng causes enhanced increases in dP/dt(max) in eNOS-/- mice compared with wild-type controls in vivo (P < 0.01) as well as in Langendorff isolated heart preparations (P < 0.02). beta-Adrenergic receptor binding (B(max)) is not significantly different in the two groups of animals (B(max) = 41.4 +/- 9.4 and 36.1 +/- 5.1 fmol/mg for wild-type and eNOS-/-). Iso-stimulated ventricular relaxation is also enhanced in the eNOS-/- mice, as measured by dP/dt(min) in the isolated heart. However, baseline ventricular relaxation is normal in eNOS-/- mice (tau = 5.2 +/- 1.0 and 5.6 +/- 1.5 ms for wild-type and eNOS-/-, respectively), whereas it is impaired in wild-type mice after NOS inhibition (tau = 8.3 +/- 2.4 ms). cGMP levels in the left ventricle are unaffected by eNOS gene deletion (wild-type: 3.1 +/- 0.8 pmol/mg, eNOS-/-: 3.1 +/- 0.6 pmol/mg), leading us to examine the level of another physiological regulator of cGMP. Atrial natriuretic peptide (ANP) expression is markedly upregulated in the eNOS-/- mice, and exogenous ANP restores ventricular relaxation in wild-type mice treated with NOS inhibitors. These results suggest that eNOS attenuates both inotropic and lusitropic responses to beta-adrenergic stimulation, and it also appears to regulate baseline ventricular relaxation in conjunction with ANP.

Gestational nicotine exposure alone or in combination with ethanol down-modulates offspring immune function

Prenatal nicotine exposure has been shown to disrupt the development of a number of peripheral organs. In the current study, we examined the effects of gestational nicotine exposure, alone or in combination with ethanol exposure, on offspring immune function. Timed pregnant rats were treated with either nicotine (6 mg/kg/day) from gestation day 4–20 using subcutaneously implanted osmotic mini-pumps or ethanol administered in the drinking water (15% w/v) from gestation day 10–20. The combined exposure group received both treatments. The ability of offspring T and B cells to proliferate in response to nonspecific stimulation by Concanavalin A or lipopolysaccharide, respectively, was determined on postnatal days 9, 15, 22, 29, 64, and 86. Offspring splenocyte β 2-adrenoceptor binding was also measured. Nicotine or nicotine+ethanol suppressed splenocyte responsiveness to Concanavalin A or lipopolysaccharide which was similar in timing and magnitude to that seen with ethanol alone. Splenocytes from these groups remained subresponsive to stimulation well into adulthood. The combined drug treatment caused an overall reduction in spleen β-adrenergic receptor binding whereas the individual drug treatments did not alter the development of spleen β-adrenergic receptors. Our results indicate that prenatal nicotine exposure can cause long-term suppression of the proliferative response of offspring immune cells. Moreover, the effects of nicotine+ethanol may cause more severe deficits in adulthood.

Effects of monocular enucleation on receptor binding and innervation pattern of the noradrenergic system in the superior colliculus of the pigmented rat

To examine visual activity-dependent regulation of the central noradrenergic (NAergic) system, we carried out in vitro autoradiography for α 2-, β-adrenergic and NMDA, non-NMDA glutamatergic receptors together with immunohistochemical analysis for dopamine β-hydroxylase in the major central visual structures, including the lateral geniculate nucleus, superior colliculus (SC), and visual cortex of pigmented rats, that had received monocular enucleation. β-Adrenergic receptor ( β-AR) binding in the SC contralateral to the enucleated eye was significantly decreased (82%, P<0.01) following monocular deprivation started at P12 and continued for 2 or 11 weeks. No significant change in β-AR binding was found in other structures examined. The number of varicosities in NAergic fibers was significantly increased following longer enucleation, i.e. for 11 weeks, in the contralateral SC (197%, P<0.001), whereas that in the ipsilateral SC was reduced (75%, P<0.001). Changes in α 2-adrenergic, NMDA, and non-NMDA glutamatergic receptor binding were small in these animals. Changes in neither β-AR binding nor innervation pattern of NAergic fibers were found in one-year-old rats that had received a comparable period of monocular enucleation. Furthermore, neither unilateral ablation of the visual cortex to reduce a different set of major afferents nor neonatal enucleation, which induced anatomical reorganization of the afferents, was found to be effective. These findings suggest that β-AR binding and innervation pattern of NAergic fibers in the SC are modified only when massive imbalance of retinal afferent activity is imposed during a limited period in early postnatal life (i.e. the sensitive period).

Long-Term Treatment of Male F344 Rats with Deprenyl: Assessment of Effects on Longevity, Behavior, and Brain Function

L-Deprenyl (selegiline) was chronically administered to male Fischer 344 rats via their drinking water beginning at 54 weeks of age (estimated daily dose: 0.5 mg/kg/day). Beginning at 84 weeks of age, the rats were behaviorally evaluated using a sensorimotor battery, a motor-learning task, and the Morris water maze. At 118 weeks of age, cerebellar noradrenergic function was evaluated in the surviving rats using in vivo electrochemistry. The rats were then sacrificed to measure brain monoamine oxidase activity and perform quantitative autoradiography to evaluate the effect of chronic deprenyl treatment on β-adrenergic receptors in the cerebellum, α 2-adrenergic receptors several brain regions, and D 1 and D 2 dopamine receptors in the striatum. Deprenyl treatment reduced brain monoamine oxidase B activity by 85%, but had no effect on brain monoamine oxidase A. A clear effect of chronic deprenyl treatment upon longevity was not observed. Several measures of CNS function were altered in the deprenyl-treated animals: 1) spatial learning in the Morris water maze was improved; 2) electrochemical signals recorded following local application of NE were reduced, and the responsiveness to the reuptake blocker nomifensine was enhanced, in the cerebellum; 3) β-adrenergic receptor binding affinity was increased in the cerebellum; 4) α 2-adrenergic receptor density was increased in the inferior colliculus; and 5) striatal D 1 dopamine receptor density was reduced but binding affinity was enhanced. In contrast, chronic deprenyl treatment did not cause changes in: 1) sensorimotor function, as evaluated by balance beam, inclined screen, or wire hang tasks; 2) motor learning; 3) α 2-adrenergic receptor density in any region examined except for the inferior colliculus, or binding affinity in any region examined; or 4) striatal D 2 dopamine receptor number or affinity. Thus, long-term oral administration of deprenyl extended the functional life span of rats with respect to cognitive, but not motor, performance.

Brain [β-adrenergic receptor binding in rats with obesity induced by a beef tallow diet

We have previously reported that compared with safflower oil diet, feeding a beef tallow diet leads to a greater accumulation of body fat by reducing sympathetic activities. The present study examined the effects of dietary fats consisting of different fatty acids on α 1- and β-adrenergic receptor binding in the hypothalamus and cerebral cortex. Male Sprague-Dawley rats were meal-fed isoenergetic diets based on safflower oil (rich in n-6 polyunsaturated fatty acids) or beef tallow (rich in saturated fatty acids) for 8 Weeks. Binding affinities of the β-adrenergic receptor in the hypothalamus and cortex were significantly lower in the beef tallow diet group, but those of the α 1-receptor did not differ between the two groups. The polyunsaturated to saturated fatty acid (P/S) ratio and fluidities of plasma membranes in the hypothalamus and cortex were lower in the beef tallow diet group than in the safflower oil diet group. These results suggest that the beef tallow diet decreases membrane fluidity by altering the fatty acid composition of plasma membranes in the hypothalamus and cerebral cortex of rat. Consequently, β-adrenergic receptor binding affinities in the brain were lower in rats fed the beef tallow diet than in rats fed the safflower oil diet. We recognized that there is possible link between the membrane fluidity and the changes in affinity of β-adrenoceptors in rat brain.

Down-regulation of β-adrenergic receptor following long-term monocular deprivation in cat visual cortex

To examine how adrenergic receptor binding is modified by experimental manipulation of sensory afferent, we carried out binding experiments (membrane fraction and in vitro autoradiography) for both α 2- and β-adrenergic receptors in the brain of cats which had been deprived of vision in one eye. In the cerebral cortex of control animals, β-adrenergic receptor (β-AR) binding was found to be higher in the occipital regions than in other regions, while α 2-AR binding was relatively uniform. Monocular deprivation throughout the postnatal sensitive period (1–7 month of age) significantly decreased β-AR binding in the visual cortex and lateral geniculate nucleus. Scatchard plot analysis in the visual cortex showed ca. 50% reduction in B max and little change in K d No significant difference was found in α 2-AR binding following monocular deprivation. Similar extent of down-regulation in β-AR binding was confirmed in all layers of visual cortex using autoradiography.

Effect of pH and Lidocaine on β-Adrenergic Receptor Binding: Interaction During Resuscitation?

Epinephrine and other beta-adrenergic receptor (beta AR) agonists are often administered during cardiopulmonary resuscitation, a time when acid-base abnormalities and arrhythmias also commonly occur. We tested whether beta 2AR binding is influenced by pH or the antiarrhythmic drug lidocaine, and whether pH might influence the interaction of lidocaine with beta 2ARs. With institutional review board approval and informed consent, 32 venous blood samples were obtained from volunteers. Lymphocytes (which bear beta 2ARs similar to those found in heart) were isolated by density gradient centrifugation. Specific binding of the beta AR ligand 3H-dihydroalprenolol (3H-DHA) was determined with lidocaine concentrations ranging from 10(-6) to 10(-2) mol/L (n = 18 experiments), and with and without lidocaine (n = 10 experiments), 100 mumol/L, and with and without QX314 (a permanently charged lidocaine derivative), 1 mmol/L (n = 4 experiments). Data are presented as percent of control-specific binding measured at a pH of 7.4. Statistical analysis consisted of Spearman's rank-test. 3H-DHA-specific binding increased (p < .001) with pH. Thus, alkaline conditions favored binding of 3H-DHA to the receptor. Lidocaine inhibited 3H-DHA binding to beta 2ARs in a concentration-dependent manner. The concentration that inhibited specific binding of 3H-DHA by 50% was 3.1 x 10(-4) mol/L (95% confidence limits, 1.3 x 10(-4) to 7.5 x 10(-4) mol/L). Lidocaine potency at inhibiting beta 2AR binding also increased with increasing pH; thus, there was limited benefit (in terms of increasing binding to beta 2ARs) to increasing pH when lidocaine was present. QX314, despite being present in a 10-fold greater concentration than lidocaine, had no effect on 3H-DHA binding at any tested pH. The affinity of beta 2 ARs for both 3H-DHA and lidocaine increased with pH. Thus, the response to beta 2AR agonists (when no lidocaine is present) might be expected to be greater with normal or alkalotic pH than under acidotic conditions, supporting the correction of metabolic acidosis to achieve optimal effects from beta 2AR agonists during resuscitation.

Beef tallow diet decreases β-Adrenergic receptor binding and lipolytic activities in different adipose tissues of rat

The effects of dietary fats consisting of different fatty acids on lipolytic activity and body fat accumulation were studied in rats. Sprague-Dawley male rats were meal-fed an isoenergetic diet based on either beef tallow or safflower oil for 8 weeks. Lipolytic activities in epididymal and subcutaneous adipose tissues were lower in the beef tallow diet group than in the safflower oil diet group. Body fat accumulation was greater in rats fed the beef tallow diet versus the safflower oil diet. Norepinephrine (NE) turnover rates used as an index of sympathetic activities in adipose tissues were lower in the beef tallow diet group. β-Adrenergic receptor binding was determined with [ 3H]dihydroalprenolol. Binding affinities of β-receptors in adipose tissues were significantly lower in the beef tallow diet group. Membrane fluidities of adipose tissues were also lower in the beef tallow diet group. Membrane fluidities were correlated with the affinities of the β-receptor. We believe from these correlations that the decreases in β-receptor binding affinities are due to -the changes in membrane fluidities. The results of the present study suggest that intake of the beef tallow diet promotes body fat accumulation by reducing lipolytic activities resulting from lower β-receptor binding and sympathetic activity in adipose tissues.

Cardiac plasma membrane physical properties and β-adrenergic receptor function are unaltered in portal-hypertensive rats

We have previously demonstrated that impairment of cardiac contractility in a rat model of cirrhosis may be secondary to altered cardiac plasma membrane physical properties affecting β-adrenergic receptor function. It is unclear whether this is caused by the cirrhosis or by the portal hypertension in this model, so we studied cardiomyocyte plasma membrane physical properties, lipid composition, and β-adrenergic receptor function in a rat model of prehepatic portal hypertension without cirrhosis. Portal hypertension was induced by graded portal vein stenosis, whereas controls had a sham operation. Cardiac sarcolemmal plasma membrane physical properties were studied by fluorescent polarization methods using diphenylhexatriene and a series of anthroyloxy-stearic acids to estimate, respectively, the static and dynamic components of membrane fluidity. β-Adrenergic receptor density and binding affinity were measured using 3H-dihydroalprenolol as a radioligand. Isoproterenol-stimulated adenylyl cyclase activity was measured by radioimmunoassay. Neither the static nor the dynamic components of membrane fluidity were significantly different in portal-hypertensive rats compared with the controls. The membrane cholesterol, phospholipid content, and the cholesterol/phospholipid ratio did not differ between the two groups. β-Adrenergic receptor density and binding affinity in the portal-hypertensive rats (respectively, 1.65 ± 0.06 pmol/mg protein and 6.78 ± 0.80 nmol/L) were not different from controls (1.76 ± 0.17 pmol/mg protein and 7.25 ± 1.48 nmol/L). Isoproterenol-stimulated adenylyl cyclase activity in membranes from portal-hypertensive rats did not significantly differ from controls. We conclude that cardiac plasma membrane physical properties and β-adrenoceptor function in portal hypertensive rats remains unimpaired, suggesting that the cardiomyopathy of cirrhosis is not caused by portal hypertension per se.

Beta-adrenergic receptor-mediated calcium mobilization in the human Jurkat T cell line.

The regulation of Ca2+ mobilization by beta-adrenergic receptor in the human Jurkat T cell line was investigated. Jurkat cells had a single class of beta-adrenergic receptor binding sites. Isoproterenol (ISP) caused the increase in cytosolic free Ca2+ concentration ([Ca2+]i) in a dose-dependent manner. In the absence of extracellular Ca2+, the pretreatment with OKT3, an anti-CD3 antibody, did not affect a transient increase in [Ca2+]i induced by the subsequent addition of ISP, and vice versa. On the other hand, the pretreatment with thapsigargin abolished the response of [Ca2+]i to the subsequent additions of ISP and OKT3. In permeabilized Jurkat cells, the addition of cAMP released Ca2+ from the intracellular Ca2+ pool. Neither nimodipine nor H8, a protein kinase A inhibitor, affected the increase in [Ca2+]i induced by ISP. The results suggest that cAMP accumulated by the activation of beta-adrenergic receptor may directly release Ca2+ from the inositol trisphosphate-insensitive intracellular Ca2+ pool in Jurkat T cells.

Effect of Chronic Alcohol Consumption on the Human Locus Coeruleus

Despite reduced levels of noradrenaline and increased cortical beta-adrenergic receptor binding, there is controversy regarding the effect of chronic alcohol consumption on the noradrenergic neurons of the locus coeruleus (LC). The aim of this study is to investigate the effects of chronic alcohol consumption on the LC; in particular, to determine whether or not there is any alteration in the size or number of neurons, or other significant changes in this nucleus. Eight chronic alcoholics without additional medical complications and eight age-matched controls were selected for this study. Immunohistochemistry with antibodies against tyrosine hydroxylase (TH) was used to visualize TH-positive neurons in spaced serial 50-microns sections throughout the length of the LC. These neurons were counted and no correction factors applied. There was no significant loss of TH-positive neurons in the LC of alcoholics compared with controls who had up to 20% variation in the number of neurons between individuals. This confirms published results from one alcoholic without complications, but contradicts recent findings of a significant neuronal loss in five alcoholics, all with liver pathology. Our analysis suggests that central noradrenergic neurons in alcoholics without significant medical complications are not susceptible to alcohol neurotoxicity.

Glucocorticoids Enhance Intracellular Signaling via Adenylate Cyclase at Three Distinct Loci in the Fetus: A Mechanism for Heterologous Teratogenic Sensitization?

Although high doses of glucocorticoids are teratogenic, endogenous hormones are necessary for development. Because of the central role of cAMP to control cell differentiation, we examined the dose dependence, tissue selectivity, and critical periods involved in glucocorticoid regulation of fetal intracellular signaling mediated by adenylate cyclase. Pregnant rats were given dexamethasone at doses spanning the threshold for therapeutic effects (0.05, 0.2, and 0.8 mg/kg) on either Gestational Days 11, 12, and 13 or Days 17, 18, and 19. Development of adenylate cyclase was evaluated in cell membrane preparations using basal activity in the absence or presence of GTP, maximal G-protein activation by fluoride, and maximal catalytic subunit stimulation by forskolin-Mn2+. Even at the lowest dose, dexamethasone on gestational days 11 through 13 enhanced fetal adenylate cyclase activity by accelerating development of both the G-protein component and the catalytic subunit. As a result, supersensitivity of the response to β-adrenergic receptor stimulation by isoproterenol was also produced, even though development of β-adrenergic receptors was unaffected. Treatment with dexamethasone later in gestation similarly fostered development of both G-protein and catalytic subunit components, with selectivity for liver and heart as opposed to brain. Again, heterologous sensitization to isoproterenol stimulation was demonstrable; in addition, late gestational treatment elevated yet a third signal transduction locus, the β-adrenergic receptor binding site. These effects are likely contributors to glucocorticoid teratogenesis (high doses) or to more subtle disruption of cell development (low doses); because adenylate cyclase is at the convergence of multiple neuronal, hormonal, and environmental inputs, glucocorticoids may sensitize the cell to heterologous stimuli, lowering the threshold for teratogenesis by other agents.

The lymphoblast β-adrenergic receptor in bipolar depressed patients: effect of chronic incubation with lithium chloride

We have recently reported a study of β-adrenergic receptor binding characteristics in lymphoblast cell lines derived from patients with bipolar disorder (BD) and healthy, matched control subjects. In the present study we have investigated the effects of incubating cells from the same subjects with lithium chloride (1 mM) for 7 days prior to assay. There was no difference in β-adrenergic receptor number between control and BD cell lines and incubation with lithium had no effect on receptor number in either group. Exposure of the cells to isoprenaline (1 nM) for 24 h immediately prior to assay caused significantly less down-regulation in BD cells (15 ± 5%) than control cells (39 ± 4%), as described previously. Incubation with lithium significantly increased the down-regulation response to isoprenaline in BD cells (39 ± 6%) but not in control cells (30 ± 7%). After lithium, the agonist-induced decrease in β-AR number in BD cells was no longer significantly different from that in control cells. We conclude that lithium selectively enhanced the agonist down-regulation of β-adrenergic receptors in cells derived from patients with bipolar disorder. The functional significance of this result and the potential biochemical mechanisms responsible for this effect are discussed.