Lymphocyte beta2-adrenergic receptors and plasma catecholamine levels in lead-exposed workers

The effect of lead exposure on beta2-adrenoceptor density and catecholamine response was studied in 26 male workers and 1 female worker, exposed to lead on average for 6 years. The systolic blood pressure in lead workers (101-160 mmHg, 124.4 +/- 14.7 mmHg) was found to be significantly higher than in controls (97-134 mmHg, 115.4 +/- 10.4 mmHg, p < 0.01) as was plasma norepinephrine (0.51 +/- 0.1 microg/liter vs 0.24 +/- 0.05 microg/liter, p < 0.01). The density of lymphocyte beta2-adrenergic receptors (Bmax) in lead-exposed workers was 86% lower than that in controls (0.15 +/- 0.08 vs 1.08 +/- 0.29 fmol/0.1 x 10(6) cells; p < 0.01). The dissociation constants (Kd) of [125I]iodocyanopindolol were 93.6 +/- 42.6 and 87.9 +/- 42.7 pM in lead-exposed workers and controls, respectively. Multiple linear regression analysis showed that elevation of systolic pressure was closely related to (a) blood lead levels, (b) decreased beta2-adrenergic receptor density, and (c) increased plasma catecholamine levels in lead-exposed workers. Linear regression analysis revealed that both plasma norepinephrine levels and beta2-adrenoceptor density (Bmax) were highly correlated with both systolic blood pressures and blood lead levels in lead-exposed workers, and a highly significant negative correlation was found to exist between Bmax and plasma norepinephrine levels (r = -0.82, p < 0.001). These data therefore demonstrate that there is a close relationship between elevated plasma catecholamine levels, decreased beta2-adrenergic receptors, and elevated blood pressure in lead-exposed workers.

Regulation of right atrial beta-adrenoceptors after cardiopulmonary resuscitation in pigs

OBJECTIVE

to test the hypothesis that right atrial beta-adrenoceptors are down-regulated after CPR and administration of beta-adrenergic agents.

METHODS

after 3 min of ventricular fibrillation and 3 min of cardiac massage, 6 pigs received adrenaline (45 micrograms/kg) intravenously before defibrillation. After restoration of spontaneous circulation, dopamine was given in order to maintain the mean arterial blood pressure stable. Right atrial beta-adrenergic binding sites were determined by an equilibration binding assay using (-)-125Iodocyanopindolol.

RESULTS

plasma adrenaline (mean +/- S.E.M.) was 1.1 +/- 0.9 ng/ml (6.0 +/- 4.9 nmol/l) pre-arrest and increased to 63.8 +/- 45.8 (348.2 +/- 250.0 nmol/l) (P < 0.05) and 1034 +/- 344 ng/ml (5644 +/- 1878 nmol/l) (P < 0.05) during CPR before and after adrenaline administration. At points in time 30 and 120 min after successful CPR, plasma adrenaline was 2.4 +/- 0.5 and 1.3 +/- 0.3 ng/ml (13.1 +/- 2.7 and 7.1 +/- 1.6 nmol/l). Compared to pre-arrest, the density of high-affinity beta-adrenoceptors was 29.0 +/- 12.8 fmol/mg pre-arrest and was 69.4 +/- 21.6 and 84.2 +/- 16.7 fmol/mg (P < 0.05 vs. pre-arrest) 30 and 120 min after CPR. The density of low-affinity as well as of total binding sites was not significantly changed after CPR.

CONCLUSIONS

it is concluded that markedly elevated plasma catecholamine concentrations after CPR and administration of adrenaline and dopamine do not lead to a decrease in the total density of beta-adrenoceptors but to an increase in high-affinity beta-adrenoceptors in right atrial cells.

Down-regulation of angiotensin II receptors in hypertrophied human myocardium

1. Specific [125I]-angiotensin II (AngII) binding in normal and hypertrophied human myocardial membranes was saturable and of high affinity. Low concentrations of unlabelled AngII and saralasin competed with [125I]-AngII for the binding sites in these tissues. Thus, saturable [125I]-AngII binding in human myocardium exhibited pharmacological specificity that characterized high affinity receptors for AngII. 2. There was little difference in the apparent dissociation constant (Kd) values for [125I]-AngII binding between normal and hypertrophied human myocardium, whereas the maximal number of binding sites (Bmax) was significantly (51%) lower in the hypertrophied group. Further, PD123177, a selective antagonist of the AT2 receptor subtype, showed three orders of magnitude higher affinity for [125I]-AngII binding sites in both normal and hypertrophied myocardium than losartan, a selective antagonist of the AT1 receptor subtype; the Hill coefficients for these drugs were close to one. 3. A significant decrease in Bmax and Kd values for (-)-[125I]-iodocyanopindolol binding between normal and hypertrophied human myocardium rarely occurred. 4. The present study suggests that both normal and hypertrophied human myocardium predominantly contains the AT2 receptor subtype and that these receptors are down-regulated in hypertrophied tissues.

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.

Functional and binding characteristics of long-acting beta 2-agonists in lung and heart

Salmeterol and formoterol, two new long-acting beta 2-agonists were equipotent (values of negative log molar concentration eliciting half-maximal effect [pD2] 9.2 +/- 0.03 and 8.9 +/- 0.03, respectively) in relaxing maximally contracted guinea pig tracheal spirals (histamine, 100 microM). Both agonists were 10 times more potent than L-isoproterenol and fenoterol and 100 times more potent than albuterol. L-Isoproterenol and fenoterol induced > 90% relaxation (percentage of maximal aminophylline relaxation). Formoterol and albuterol were equally efficacious. Formoterol was more efficacious (86 +/- 5%) than salmeterol (62 +/- 3%) or soterenol (59 +/- 3%). In minimally contracted tissues (10 microM histamine), agonist potencies increased 10-fold and relaxation was complete. In [125I]iodocyanopindolol-labeled bronchial membranes, formoterol and salmeterol induced high-affinity states of the beta 2-receptor (pKh 9.6 +/- 0.4 and 10.4 +/- 0.7, respectively), the former inducing a higher percentage (57 +/- 6 versus 28 +/- 4, p < 0.05). Only low-affinity binding (pKI) was observed when guanine nucleotide was present. pD2 values were similar to pKh values and relative efficacies significantly correlated with percentage of pKI sites. Formoterol and salmeterol were highly selective for the beta 2 versus beta 1-subtype (pKI values were 8.2 +/- 0.09 and 6.25 +/- 0.06 and 8.3 +/- 0.04 and 5.7 +/- 0.04, respectively). Albuterol (5.83 +/- 0.06 and 4.71 +/- 0.16) and fenoterol (6.33 +/- 0.07 and 5.67 +/- 0.05) were less selective. These results can explain the potencies and efficacies of salmeterol and formoterol in humans.

Evidence of classic beta 3-adrenergic receptors in porcine adipocytes

Adipocytes from several mammalian species have predominant beta 3-adrenergic receptors (beta 3-AR). Attempts to classify porcine adipocyte beta-adrenergic receptors (beta-AR) into subtypes have not been successful. Selectivity of agonists and antagonists for stimulation of lipolysis and for ligand binding is considerably more restrictive than for the classic rat and guinea pig beta-AR subtypes. The unique pattern for activity of agonists and antagonists in porcine beta-AR precludes analogy to classic receptors and consequently there is no conclusive evidence regarding porcine beta-AR subtypes. Porcine adipocyte membranes were used in ligand binding experiments designed specifically to demonstrate beta 3-AR. Equilibrium saturation curves with dihydroalprenolol, CGP 12,177, or iodocyanopindolol indicated saturation at low concentrations with a single binding site. Equilibrium competitive ligand binding with iodocyanopindolol as radioligand and isoproterenol or propranolol as competitive ligands indicated both ligands totally inhibited radioligand binding; propranolol was more potent than isoproterenol. Nonradioactive CGP 12,177 also competed with iodocyanopindolol. Ligand binding experiments provided no evidence of a low-affinity beta-AR (binding at high concentrations of ligand), the beta 3-AR. Positive evidences of a beta 3-AR were that CGP 12,177, a beta 1- and beta 2-adrenergic receptor antagonist but a beta 3-AR agonist, partially stimulated porcine adipocyte lipolysis. Furthermore, transcripts for a beta 3-AR, as well as a beta 1- and beta 2-AR, have been demonstrated in RNA from porcine adipocytes in other studies. The beta-AR subtypes expressed and functional in porcine adipocytes remain unknown. The multiple ligand binding sites cannot be attributed to classic beta-AR subtypes. The porcine beta-AR may be a single unique receptor to impart atypical binding properties, or more likely, multiple subtypes, each different enough from classic subtypes to impart the unique properties observed.

Indices of brain beta-adrenergic receptor signal transduction in the learned helplessness animal model of depression

Both stress response and antidepressant drug action may be mediated by beta-adrenergic receptors (beta AR). Since learned helplessness is a stress-induced animal model of depression, beta AR are relevant to investigate in this model. To date, studies have measured changes in total receptor density (RT), but have not examined more detailed aspects of signal transduction mechanisms such as coupling of the receptor to GS protein. We have investigated brain beta AR coupling in the frontal cortex, hippocampus and hypothalamus of rats exposed to inescapable shock and then tested for learned helplessness, and in both tested and naive controls using [125I]-iodocyanopindolol (ICYP) as the ligand. Both antagonist-saturation and agonist-displacement experiments were conducted, and the specificity for the beta AR was optimized by excluding ICYP binding to 5HT1B receptors. The percentage receptor density in the high-conformational state (%RH) and the ratio of agonist (isoproterenol) dissociation constant from the receptor in the low-/high-conformational states (KL/KH) were used as indices of coupling to GS protein. No significant differences were found between rats developing learned helplessness and non-helpless rats after inescapable stress in any parameter measured in any brain region. In the frontal cortex, exposure to inescapable shock induced beta AR uncoupling from GS protein as suggested by a low KL/KH ratio both in helpless and non-helpless rats but not in either control group. In the hypothalamus, there were trends for higher RL, RT and KL/KH ratio in helpless rats and stressed controls compared to naive controls. These findings suggest that beta AR binding parameters in frontal cortex, hippocampus or hypothalamus did not differentiate between helpless and non-helpless rats. Changes in beta AR coupling observed in these brain regions may reflect effects of stress, which appeared to be region-specific, rather than stress-induced behavioral depression.

Binding affinity of sarpogrelate, a new antiplatelet agent, and its metabolite for serotonin receptor subtypes

We analyzed the displacement activity of sarpogrelate and its active metabolite (M-1) in the radiolabeled ligand binding to various 5-hydroxytryptamine (5-HT) receptor subtypes using rat brain cortical membranes. Sarpogrelate was shown to have the same affinity as ritanserin for 5-HT2A receptors, with a Ki value of 8.39 nM. The active metabolite of sarpogrelate, M-1, was more active than sarpogrelate itself and of ritanserin, with a Ki value of 1.70 nM. Both sarpogrelate and M-1 had no affinity for 5-HT1A receptors, but these substances, at a concentration of 10 microM, displaced the specific binding to the 5-HT1B receptors of [125I]iodocyanopindolol, resulting in Ki values of 0.881 and 0.859 microM, respectively. The Ki values of sarpogrelate and M-1 are almost the same as that of ritanserin, a specific 5-HT2 receptor antagonist. Sarpogrelate and M-1, as well as ritanserin, are shown to have very low affinity for 5-HT1B receptors. Both sarpogrelate and M-1 had no affinity for 5-HT3 receptor subtypes. In the 5-HT4 receptor binding experiments, sarpogrelate exhibited almost no affinity, while M-1, at the concentration of 10 microM, displaced the binding activity, resulting in a Ki value of 0.838 microM. Both drugs had a weak antagonistic effect on a 5-HT4 receptor-mediated function, i.e., the 5-HT-induced relaxation of rat isolated esophageal tunica muscularis mucosae. In conclusion, sarpogrelate and M-1 have high affinity for 5-HT2A receptors with a relatively high selectivity.

Atypical responses of rat ileum to pindolol, cyanopindolol and iodocyanopindolol

1. Pindolol, cyanopindolol (CYP) and iodocyanopindolol (IodoCYP) have been reported to act either as antagonists, agonists or partial agonists at the beta 3-adrenoceptor in different preparations. A comprehensive investigation has not yet been described with these compounds tested in one tissue from one species. This study was conducted to delineate the pharmacological effects of pindolol, CYP and IodoCYP and to provide data on their affinities at the predominant beta-adrenoceptor in rat ileum. 2. The beta-adrenoceptors present in rat ileum were characterized in the presence of CGP 20712A and ICI 118 551, atropine and corticosterone, with (-)-isoprenaline used as an agonist. The role of the beta 1 and beta 2-adrenoceptors was determined by the omission of either CGP 20712A, ICI 118 551, or both, from the buffers. Conversely, the effectiveness of the beta 1- and beta 2-adrenoceptor blockade was examined by use of the beta 1-adrenoceptor-selective agonist, RO 363 and the beta 2-adrenoceptor-selective agonist, salbutamol. 3. There was no evidence for the presence of functional beta 1-adrenoceptors, and no strong evidence that beta 2-adrenoceptor stimulation contributed to the relaxant effects of (-)-isoprenaline. (-)-Phenylephrine did not produce relaxation of the tissue and 5-hydroxytryptamine produced contraction. 4. The beta 3-adrenoceptor-selective agonist, BRL 37344 and (-)-isoprenaline were potent full agonists (pD2 8.35 +/- 0.04 and 7.76 +/- 0.14 respectively), whereas ICI D7114 was less potent (pseudo pD2 6.92 +/- 0.15). These results indicate that the predominant functional beta-adrenoceptors in rat ileum are beta 3-adrenoceptors. 5. Partial agonist effects were produced by CYP (pD2 5.28 +/- 0.26) and IodoCYP (pD2 7.0 +/- 0.26), but not pindolol. All three compounds antagonized the effects of (-)-isoprenaline with pKb values of 6.68 +/- 0.10, 7.59 +/- 0.07 and 7.59 +/- 0.11 for pindolol, CYP and IodoCYP respectively. Likewise, CYP and IodoCYP antagonized the effects of BRL 37344 with pKb values of 7.20 +/- 0.22 and 7.21 +/- 0.14 respectively. This study provides the first functional data on the effects of IodoCYP, the ligand with the highest known affinity for the beta 3-adrenoceptor, at the characterized rat ileum beta 3-adrenoceptor. 6. In conclusion, whereas pKb values suggest that CYP and IodoCYP have a similar affinity for the beta 3-adrenoceptor in rat ileum, the higher potency of IodoCYP suggests that it promotes a greater coupling efficiency, or that its partial agonist effects are produced through a site other than the beta 3-adrenoceptor. The similar pKb values for CYP and IodoCYP at the beta 3-adrenoceptor contrast with their order of known affinities at the beta 1- and beta 2-adrenoceptors, where IodoCYP is far more potent than CYP. This provides evidence of further differences in the characteristics of the beta 3-adrenoceptors compared to the beta 1- and beta 2-adrenoceptors. Finally, the utility of IodoCYP as a beta 3-adrenoceptor antagonist would appear to be limited because of the greater magnitude of partial agonist effects that it produces.

Catecholamines modulate growth and differentiation of human preosteoclastic cells

Using a clonal cell line of human osteoclast precursors (FLG 29.1 cells), that after treatment with 12-O-tetradecanoyl phorbol 13-acetate (TPA) show many functional characteristics of osteoclasts, we demonstrated that catecholamines act as inducers of osteoclast maturation in vitro and as stimulators of osteoclast activity via the binding to beta 2 adrenergic receptors. Scatchard analysis of 125I-labelled iodocyanopindolol to untreated (undifferentiated) or TPA-treated (differentiated) FLG 29.1 cells revealed the presence of a single high-affinity site with a Kd value around 24 pM and 8 pM respectively and with superimposable binding capacity (1.18 fmol/mg protein). Catecholamines increased in a dose-dependent fashion the intracellular cyclic AMP (cAMP) accumulation in both undifferentiated and TPA-treated FLG 29.1 cells. Pretreatment of untreated and TPA-treated FLG 29.1 cells with propranolol inhibited the catecholamine effect on cAMP accumulation, while pretreatment with clonidine had no effect. Catecholamines also reduced cell proliferation, increased tartrate-resistant acid phosphatase (TRAcP) activity, interleukin 6 (IL-6) production, multi-nuclearity and response to salmon calcitonin (sCT) in undifferentiated FLG 29.1 cells. In differentiated FLG 29.1 cells only IL-6 release was induced by catecholamine treatment. These findings support a potential role for catecholamines in modulating osteoclast differentiation and mature osteoclast activity.

Initial externalization followed by internalization of beta-adrenergic receptors in rat heart during sepsis

Changes in the distribution of beta-adrenergic receptors in two subcellular fractions, the sarcolemma and the light vesicle, of rat heart during sepsis were studied, using [3H]dihydroalprenolol ([3H]DHA) binding and photoaffinity labeling with [125I]iodocyanopindolol ([125I]ICYP). Sepsis was induced by cecal ligation and puncture (CLP). Septic rat hearts exhibit an initial hypercardiodynamic (9 h after CLP; early sepsis) and a subsequent hypocardiodynamic (18 h after CLP; late sepsis) state. [3H]DHA-binding studies show that, during early sepsis, the maximum binding capacity (Bmax) was increased by 35% in sarcolemma but was decreased by 25% in light vesicles, whereas during late sepsis, the Bmax was decreased by 39% in sarcolemma but was increased by 30% in light vesicles. Photoaffinity labeling studies show that the incorporation of [125I]ICYP into 64,000-Da peptide during early sepsis was increased by 32% in sarcolemma but was decreased by 27% in light vesicles, whereas during late sepsis, the incorporation was decreased by 30% in sarcolemma but was increased by 35% in light vesicles. These data indicate that beta-adrenergic receptors in the rat heart were externalized from light vesicles to sarcolemma during the hyperdynamic phase but were internalized from surface membranes to intracellular sites during the hypodynamic phase of sepsis. Because beta-adrenergic receptors mediate adrenergic control of cardiac muscle contraction, a biphasic intracellular redistribution of beta-adrenergic receptors in the heart may contribute to the development of the initial hypercardiodynamic and subsequent hypocardiodynamic states during sepsis.

Burn injury alters beta-adrenergic receptor and second messenger function in rat ventricular muscle

OBJECTIVES

The molecular pharmacologic bases for the attenuated cardiovascular and metabolic responses to catecholamines, after burn injury, have not been elucidated. In the present study, myocardial tissues were used as a model of beta-adrenergic receptors to study burn injury-induced alterations in receptors and in signal transduction.

DESIGN

Prospective study, randomized to treatment and control groups.

SETTING

University-hospital research laboratory.

SUBJECTS

Male Sprague-Dawley rats (180 to 210 g).

INTERVENTIONS

A 50% body surface area burn or sham-burn was administered to the rats.

MEASUREMENTS AND MAIN RESULTS

Myocardial membranes were isolated at 24 hrs, 7 days and 14 days after 50% body surface area scald or sham injury. (-)125I-iodocyanopindolol was used to assess maximal binding capacity and affinity of the beta-adrenergic receptor. Basal and stimulated concentrations of second messenger, cyclic adenosine monophosphate (cAMP), were also assessed. Production of cAMP during isoproterenol stimulation tested the integrity of the beta-adrenergic receptor-mediated signal transduction. Forskolin, which stimulates adenylate cyclase enzyme directly (bypassing the receptor and G protein) to produce cAMP, tested the efficacy of the enzyme itself. Maximal binding capacity was unaltered between the experimental and control groups, but the affinity (mean +/- SEM) was significantly decreased in burned animals at 7 days (125.4 +/- 15.5 picomoles [pmol]; p = .01) and at 14 days (216.7 +/- 50.7 pmol; p = .001) compared with controls (75.5 +/- 8.4 pmol). In different set experimental and control groups, basal concentrations of cAMP in myocardial membranes were significantly decreased in burned animals at 7 days (control 38.6 +/- 4.2 vs. 5.8 +/- 0.9 pmol/mg of protein/min; p = .003) and at 14 days (control 47.4 +/- 3.2 vs 28.3 +/- 6.6 pmol/mg of protein/min; p = .002). The forskolin (direct)-stimulated synthesis of cAMP was decreased in burned animals at 24 hrs (control 339.0 +/- 40.5 vs. 214.4 +/- 16.6 pmol/mg of protein/min; p = .01), at 7 days (control 289.0 +/- 34.4 vs. 32 +/- 13.0 pmol/mg of protein/min; p = .01), and at 14 days (control 322.9 +/- 28.6 vs. 137.0 +/- 46.1 pmol/mg of protein/min; p = .01). The isoproterenol or receptor-mediated stimulation of cAMP production was also significantly (p < .001) impaired in burned animals compared with controls at 24 hrs (control 134.7 +/- 11.9 vs. 83.1 +/- 13.3 pmol/mg of protein/min), and at 14 days (control 128.2 +/- 7.2 vs. 92.8 +/- 17.7 pmol/mg of protein/min).

CONCLUSION

The etiology of the decreased responses in the myocardium to exogenous and endogenous beta-adrenergic receptor agonists after burn injury may be attributed to decreased affinity for ligands, and also to impaired receptor-mediated signal transduction and to decreased adenylate cyclase enzyme activity, resulting in decreased basal and stimulated second messenger (cAMP) production.

Effects of stress on the functional properties of pre- and postsynaptic 5-HT1B receptors in the rat brain

Numerous studies have clearly shown that the turnover and release of serotonin (5-hydroxytryptamine, 5-HT) are increased under acute stressful conditions. Inasmuch as this latter process is under the control of a feedback mechanism involving the stimulation of presynaptic 5-HT1B autoreceptors, we have investigated the possible effects of acute restraint (40 min) on the functional properties of 5-HT1B receptors. The efficacy of the selective 5-HT1B receptor agonist 3-[1,2,5,6-tetrahydropyrid-4-yl]pyrrolo-[3,2-b]pyrid-5-one (CP-93,129) in inhibiting in vitro the K+-evoked release of [3H]5-HT, was significantly reduced in stressed rats as compared to naive animals. Similarly, the responsiveness of 5-HT1B receptors inhibiting the release of [3H]acetylcholine (presynaptic 5-HT1B heteroreceptors), was reduced by restraint. These effects were observed in the hippocampus, but using the inhibitory effect of CP-93,129 on forskolin-stimulated adenylyl cyclase activity as an index of 5-HT1B receptor function, it could be shown that the 5-HT1B receptors located in the substantia nigra are also desensitized by stress. The number as well as the apparent affinity constant of 5-HT1B binding sites labelled by [125I]iodocyanopindolol, as measured by quantitative autoradiography and membrane binding, were similar in naive and restraint-stressed rats suggesting that the stress-induced desensitization of 5-HT1B receptors is not due to a reduced number of 5-HT1B binding sites. As stress is thought to be a causal factor for the etiology of anxiety and depression, these results support the potential involvement of 5-HT1B receptor dysfunction in the development of these neurological disorders.

Beta 2-adrenoceptor density of human lymphocytes after nitroprusside-induced hypotension

The present study was undertaken to assess the influence of nitroprusside-induced hypotension on beta 2-adrenoceptor density. Twenty-four patients undergoing nose-septum corrections under general anesthesia were allocated randomly to a nitroprusside or control group. beta 2-Receptor density on lymphocytes was measured by binding studies using (-)125-iodocyanopindolol. Lymphocyte subpopulations B, T, Thelper, Tsuppressor, and natural killer cells were determined simultaneously by flow cytometry. Five of 12 nitroprusside-treated patients developed significant intraoperative increases of epinephrine levels (+69% versus preoperatively) which were not seen in the remaining seven patients. In these five patients, beta 2-receptor density of unfractionated lymphocytes was 26% lower (P < 0.05) on the first day after surgery compared with preoperative values. Since no changes in proportions of lymphocyte subpopulations were observed, these results are not caused by redistribution phenomena inducing a decrease of subsets with a high number of beta receptors. These findings suggest that beta 2-adrenergic responsiveness might be diminished after nitroprusside treatment in some patients.

Characterization of alpha 2 adrenoceptors and other adrenoceptors in membranes isolated from dog mesenteric nerve axons

The axonal membranes from dog mesenteric nerves were isolated and characterized. They had a high density of [3H]saxitoxin, [3H]rauwolscine and [125I]iodocyanopindolol binding sites, but low densities of [125I] omega-conotoxin (GVIA) and [3H]prazosin binding sites. The microsomal membranes had one of the higher densities of [3H]rauwolscine binding sites in centrifugation fractions. These sites were characterized by saturation, kinetic and competition studies. In competition with oxymetazoline, WB 4101, prazosin, ARC-239, SK&F 104078 and SK&F 104856, these rauwolscine binding sites were alpha 2A-like. Chloroethylclonidine pretreatment did not affect the ability of SK&F 104078 or SK&F 104856 to compete with rauwolscine binding sites on axonal membranes. Bmax values were unchanged by chloroethylclonidine under conditions that also failed to reduce Bmax values of rauwolscine binding to membranes from human platelets. These receptors appear to be alpha 2A adrenoceptors and may represent sites of prejunctional control of neurotransmitter release in the dog. This membrane preparation may be useful in biochemical studies of prejunctional neural receptors.

Modulation of cardiac physiology by an anti-Trypanosoma cruzi monoclonal antibody after interaction with myocardium

Circulating antibodies from human and murine chagasic sera are able to interact with myocardium, activating neurotransmitter receptors. Here, we studied the effects of a monoclonal antibody (MAb CAK20.12), which recognizes a 150 kilodalton antigen of Trypanosoma cruzi and reacts with normal human and murine striated muscles and with cardiac tissue. The MAb CAK20.12 binds to purified cardiac membranes and interferes with the binding of beta-adrenergic receptor radioligand ([125I]CYP) and muscarinic cholinergic receptor (mAChR) radioligand ([3H]QNB) in a noncompetitive way. As a consequence of this interaction, beta-adrenergic receptor and mAChR were activated, leading to increased intracellular levels of cyclic AMP as a result of beta-adrenergic receptor-coupled adenylate cyclase triggering. When its sympathetic action was abrogated, it also induced an mAChR-mediated increase in cyclic GMP. Furthermore, cardiac physiology was modified by MAb CAK20.12, as it was able to increase cardiac contractility through beta-adrenoceptor activation and to decrease atrial frequency as a result of mAChR activation. The fact that this MAb modulates and modifies the mechanical and biochemical activity of normal murine heart established an important basis for future research and understanding of how the host's humoral immune response acts on the course and development of the chronic chagasic myocardiopathy.

Differential coupling of glucagon and beta-adrenergic receptors with the small and large forms of the stimulatory G protein

Glucagon receptors (GRs) and beta-adrenergic receptors (beta-ARs) stimulate adenylate cyclase (AC) via Gs. The present study was performed to determine whether different cAMP-generating receptors share the same pool of Gs. In hepatocytes and liver plasma membranes from partially hepatectomized male rats, glucagon was more potent in stimulating AC than beta-adrenergic agonists, but the effects of glucagon and beta agonists on AC activity were not additive. This suggests that GRs and beta-ARs share the same pathway. Glucagon lowered the affinity of beta agonists for beta-ARs in the presence of GTP gamma S, whereas beta agonists had no effect on glucagon binding to GRs regardless of the presence or the absence of GTP gamma S. Therefore, the pool of Gs coupled to GRs appears to include that coupled to beta-ARs. The alpha subunit of Gs (Gs alpha) exists in small (Gs alpha-S) and large (Gs alpha-L) forms. Recently, with a new method that uses tryptic digestion, the G protein coupled to beta-ARs was identified as Gs-L in partially hepatectomized male rat livers because beta-adrenergic agonists promoted trypsinization of Gs alpha-L but not of Gs alpha-S. By contrast, the present study showed that glucagon enhanced the sensitivity of the two Gs alpha isoforms to trypsin in a concentration-dependent manner, indicating that GRs are coupled to both Gs alpha-S and Gs alpha-L. In conclusion, GRs share a common Gs-L with beta-ARs but are also coupled to another Gs, Gs-S, in partially hepatectomized male rat livers.

Multiple mechanisms of heterologous beta-adrenoceptor regulation in rat uterus

The inhibitory effects of catecholamines on rat myometrium mediated by beta-adrenoceptors are modulated by ovarian steroids. Previously reported findings of radioligand binding studies on myometrial membranes have demonstrated changes in the numbers of beta-adrenergic binding sites following ovarian steroid treatment. However, these changes were not accompanied by parallel functional changes. In the present study, we have investigated possible mechanisms of heterologous beta-adrenoceptor regulation by ovarian steroids. Binding studies were performed on myometrial membrane and cytosolic preparations from rats which had been ovariectomized and subsequently received no hormonal treatment or had been treated with oestradiol, progesterone or combined oestradiol and progesterone. The beta-adrenergic antagonist [125I]iodocyanopindolol and the unlabelled competing agonist, isoprenaline, were used in the present studies. Hormonal treatment had no effect on the concentration of beta-adrenergic binding sites in the myometrium (i.e. the number of membrane-bound and cytosolic binding sites per mg protein). However, significant changes were found in the total number of binding sites; these were associated with the hormone-induced tissue hypertrophy. In myometrium from ovariectomized-alone rats, approximately 50% of beta-adrenergic binding sites were present in the cytosolic fraction. Oestradiol treatment, either on its own or in combination with progesterone, resulted in the translocation of binding sites to the cell membrane. However, in the absence of progesterone only 33% of the membrane-bound binding sites bound the beta-adrenergic agonist, isoprenaline, with a high affinity, suggesting that the majority of these membrane-bound binding sites represented non-functional beta-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of bovine somatotropin and food deprivation on beta-adrenergic and A1 adenosine receptor binding in adipose tissue of lactating cows

Lactating Holstein cows were used to assess the effect of bovine somatotropin (bST; n = 8) and fasting (FAST; n = 4) on ligand binding to beta-adrenergic (BAR) and Type-1 adenosine (A1R) receptors in adipose tissue. Cows received exogenous bST (sometribove; 40 mg/d) or no hormone (control) for 4 d in a single-reversal design with a 7-d interval between treatment periods. Subcutaneous adipose tissue biopsies were taken on day 4 of each treatment. Eight d after the bST regimen, 4 cows were fasted for 3 d and adipose biopsies were taken. Ligand binding was quantified with a postnuclear, total adipose tissue membrane preparation (100,000 x g pellet). Binding to BAR and A1R was assessed with the antagonists [125I]iodocyanopindolol (ICP) and [3H]8-cyclopentyl-1,3-dipropylxanthine (DCPCX), respectively. The binding affinity (Kd) of BAR for ICP was not affected by bST but was enhanced by FAST; maximal binding (Bmax) was increased with bST treatment (P < 0.06) and reduced by FAST (61%, P < 0.01). Kd values for DCPCX binding to A1R were not changed by bST or FAST. bST did not affect Bmax for A1R; however, FAST reduced the Bmax by 38%. Data highlight the differential regulation of BAR and A1R by bST and FAST.

Interaction of the antiarrhythmic agents SR 33589 and amiodarone with the beta-adrenoceptor and adenylate cyclase in rat heart

1. The effects of SR 33589 and amiodarone on the cardiac beta-adrenoceptor were studied in vitro and after chronic treatment by means of [125I]-(-)-iodocyanopindolol ([125I]-(-)-CYP) binding and measurement of adenylate cyclase activity. 2. Binding of [125I]-(-)-CYP was inhibited in a dose-dependent manner by SR 33589 (IC50=1.8 +/- 0.4 microM, nH=0.93 +/- 0.06) and amiodarone (IC50=8.7 +/- 2.0 microM, nH=9.2 +/- 0.03). Saturation binding experiments indicated a non-competitive interaction such that SR 33589 (1 and 3 microM) and amiodarone (5 and 10 microM) reduced the Bmax of [125I]-(-)-CYP binding without any effect on the KD. Kinetic studies showed that the rate of association of [125I]-(-)-CYP was unchanged while the rate of dissociation was increased both in the presence of SR 33589 (10 microM) and amiodarone (30 microM).3. Under the same conditions, the receptor stimulated adenylate cyclase activity was inhibited in a dose-dependent, but non-competitive manner, by SR 33589 (isoprenaline-, glucagon- and secretin-stimulated enzyme inhibited 50% at 6.8 +/- 0.6 microM, 31 +/- 10 microM and 12 +/- 3 microM, respectively) while the basal, GTP- and GPP(NH)p-stimulated enzyme was inhibited by 5-10% and the NaF and forskolin-stimulated enzyme by 50% at 500 microM. Amiodarone exhibited a similar pattern of inhibition. 4. After chronic oral treatment (50, 100, 150 mg kg(-1) per day, 14 days), both SR 33589 and amiodarone produced a dose-dependent decrease in Bmax without any effect on KD as determined from [125I]-(-)-CYP saturation experiments and a decrease of the isoprenaline- and glucagon-stimulated adenylate cyclase activity without any effect on basal enzyme activity or activity when stimulated by agents acting directly on regulatory catalytic units. 5. Unlike amiodarone, SR 33589 does not contain iodine substituents. Plasma levels of T3, T4, and rT3 were changed after SR 33589 treatment except a decrease in T4 level at the highest dose whilst the T4 T3 ratio and the level of rT3 were dose-dependently increased by amiodarone treatment. 6. In vitro, SR 33589 and amiodarone were characterized as non-competitive beta-adrenoceptor antagonists. Chronic treatment led to a down-regulation of the beta-adrenoceptor; the down-regulation cannot be attributed to an indirect effect mediated by the thyroid hormones. To reconcile these opposing observations, we propose that SR 33589 and amiodarone interact with the beta-adrenoceptor at a site close to the intracellular loops which are involved in the coupling with Gs and contain the phosphorylable sites.

Determination of structural domains for G protein coupling and ligand binding in beta 3-adrenergic receptor

The beta 3-adrenergic receptor (beta 3AR) is a member of the super-family of G protein-coupled receptors that are characterized by seven putative transmembrane helices connected by hydrophilic loops. The mechanism by which the activated beta ARs transmit the signals across the plasma membrane involves the stimulation of Gs, which in turn activates adenylyl cyclase, yielding the second messenger cAMP. In the present study, we created a series of mutant beta 3ARs to explore the structural basis for the subtype-specific binding of BRL 37344, a beta 3-selective agonist, and for the coupling of the receptor to Gs. To study the mechanism of subtype-specific binding of BRL 37344, chimeric beta 2/beta 3ARs were constructed and expressed in Raji cells. Binding studies suggest that the transmembrane segment 5 region of the beta 3AR contains critical determinants for observed high affinity for BRL 37344. Previous studies of beta 2ARs have demonstrated a role for the third intracellular loop in activating Gs. To investigate the role of this region in the beta 3AR, we constructed mutant beta 3ARs lacking a small segment of the amino- or carboxyl-terminal domain of the third intracellular loop. Expression of these mutant receptors in mouse L cells and Raji cells reveals that although both mutants are capable of binding the antagonist [125l]iodocyanopindolol, the agonist-stimulated cAMP production mediated by these mutant receptors is markedly attenuated or abolished. In addition, both mutant beta 3ARs exhibit an approximately 10-fold increase in affinity for agonist binding, whereas the affinity for antagonists is not affected. This increased agonist affinity is not altered by treatment with 100 microM 5' quanylyl-imidodiphosphate, suggesting that these mutant receptors are uncoupled from G proteins. The results of the present study demonstrate that these regions of the third intracellular loop of beta 3AR are critical for coupling to G proteins and suggest a role for these regions in maintaining the resting state of the unliganded receptor.

Determination of beta-adrenoceptor subtype on rat isolated ventricular myocytes by use of highly selective beta-antagonists

1. The relative proportions of beta 1- and beta 2-adrenoceptors were determined by radioligand binding studies in three different rat myocardial preparations: membranes prepared from rat ventricle (ventricular membranes), membranes prepared from rat isolated ventricular myocytes (myocyte membranes), and myocytes isolated from rat ventricle (myocytes). 2. Competition experiments using CGP 20712A or ICI 118,551 with [125I]-iodocyanopindolol ([125I]-ICYP) revealed high- and low-affinity binding sites in ventricular membranes. The concentration at which each beta-antagonist occupied 100% of its high-affinity binding sites was 300 nM for CGP 20712A (beta 1-adrenoceptor) and 50 nM for ICI 118,551 (beta 2-adrenoceptor). 3. The density of high-affinity (beta 1-adrenoceptor) and low-affinity (beta 2-adrenoceptor) binding sites for CGP 20712A was measured by a saturation experiment using [125I]-ICYP in the presence and absence of 300 nM CGP 20712A. In ventricular membranes, the proportions of high-affinity and low-affinity binding sites for CGP 20712A were 73% and 27%, respectively, whereas in myocyte membranes, the corresponding figures were 90% and 10%, respectively. The density of low-affinity binding sites for CGP 20712A in ventricular membranes, defined as [125I]-ICYP-specific binding in the presence of 300 nM CGP 20712A, was decreased by addition of 50 nM ICI 118,551, whereas that in myocyte membranes was not affected. 4. In myocytes, specific binding of [125I]-ICYP and [3H]-CGP 12177 was not detected by saturation experiments performed in the presence of 300 nM CGP 20712A. 5 In myocytes, the activation of adenylate cyclase caused by beta2-adrenoceptors was not detected in the presence of 10 nM, 100 nM or 1000 nM CGP 20712A, which selectively antagonized beta1-adrenoceptors.Furthermore, the concentration-response curve for isoprenaline-stimulated cyclic AMP accumulation was not shifted by 10 nm or 100 nM ICI 118,551, which selectively antagonized beta2-adrenoceptors, but was shifted to the right by 1000 nM ICI 118,551.6 These results indicate that beta2-adrenoceptors are not present on rat ventricular myocytes and that beta2-adrenoceptor stimulation does not cause any detectable production of cyclic AMP. We conclude that only beta1-adrenoceptors exist on rat ventricular myocytes.

Beta-adrenergic mitogenic signal transduction in peripheral lung adenocarcinoma: implications for individuals with preexisting chronic lung disease

Peripheral adenocarcinoma (PAC) of the lung has increased dramatically over the last 20 years and is today the leading histological type of lung cancer in smokers and nonsmokers in industrialized countries. There is no apparent explanation for the steep rise in the number of individuals developing this cancer type. Using assays for the assessment of cell proliferation, receptor binding, and production of cyclic AMP (cAMP), we have identified a beta-adrenergic receptor-mediated mitogenic pathway, which activates cAMP down-stream, in cell lines derived from human peripheral adenocarcinomas that express features of Clara cells. Agonists of beta-adrenergic receptors strongly stimulated cell proliferation, whereas antagonists of this receptor and its associated second messenger, cAMP, were potent inhibitors of this effect. Agonists of beta-adrenergic receptors are the active ingredients of many decongestants and bronchodilators, and such medications are, therefore, likely to stimulate this pathway in vivo. Patients suffering from chronic upper and lower respiratory tract diseases and treated with such medications over many years may, therefore, be at a higher risk than the average population to develop PAC, particularly when simultaneously exposed to carcinogenic environmental factors such as smoking. Because the incidence of chronic respiratory tract diseases has risen in industrialized countries during the same time frame as PAC, a potential etiological link between the therapy of such nonneoplastic diseases with beta-adrenergic agonists and the risk for PAC should be investigated.

Effect of theophylline on beta-adrenergic receptor density and cAMP content in bovine aortic smooth muscle cells

Activation of vascular beta-adrenergic receptors prevents an increase in vascular permeability caused by free radicals or inflammatory peptides. Methylxanthines seem to have similar protective effects on vascular endothelium. In the present study we investigated the effect of theophylline on the beta-adrenergic receptor expression and cAMP concentrations in cultured endothelial and smooth muscle cells from bovine aorta. Comparable values for beta-receptor density and binding affinity were detected in both cell types. Isoproterenol induced significant downregulation of beta-receptors in endothelial (BAEC: -60.5%) and smooth muscle cells (BASMC: -52.5%; P < 0.01). Incubation of endothelial cells with theophylline (4 micrograms/ml and and 40 micrograms/ml) for 24 hours did not affect beta-receptor expression, whereas in smooth muscle cells the beta-receptor density was reduced for -31.5% and -28.7%, respectively. In endothelial cells a transient effect on cAMP concentrations was observed after stimulation with isoproterenol (1 microM), but no effect was found in theophylline treated endothelial cells. Stimulation of intact smooth muscle cells with isoproterenol and theophylline (4 micrograms/ml and 40 micrograms/ml) resulted in a significant increase of cAMP concentrations after 60 and 240 minutes. The present data suggest a novel, celltype specific effect of theophylline on the beta-adrenergic receptor expression in vascular smooth muscle cells in vitro.

Beta-adrenergic receptor changes in learned helplessness may depend on stress and test parameters

Behavioral deficits following inescapable stress (learned helplessness) may serve as an animal model of depression. Previous studies using foot-shock stress to induce learned helplessness and a bar-press test for the stress-induced behavioral deficit have found increased beta-adrenergic receptor density in the hippocampus of learned helpless rats. We replicated these experiments using a tail-shock stress and the shuttle-box test. In our experiments, rats that developed learned helplessness after inescapable stress did not demonstrate any significant differences in beta-adrenergic receptor density or affinity in the frontal cortex, cerebellum, or hippocampus compared to the nonhelpless rats, nor to the tested control rats. These results suggest that beta-adrenergic receptor changes in learned helplessness may depend on the specific stress and test procedures used.