Alpha 2-adrenergic Receptor Binding Research Articles

Altered platelet alpha 2-adrenergic receptor binding sites in borderline personality disorder

The authors found significantly fewer total platelet alpha 2-adrenergic receptor binding sites in 13 nonmedicated patients with borderline personality disorder than in 11 patients with borderline personality disorder who were receiving low doses of benzodiazepines and 18 nonpsychiatric control subjects. The two patient groups showed comparable degrees of depression as assessed by the Hamilton Rating Scale for Depression. However, nonmedicated borderline patients were considerably more anxious than medicated patients, raising the possibility that lower alpha 2-adrenergic receptor binding in borderline personality disorder is related to anxiety.

Comparison of α1‐Adrenergic Receptor‐Stimulated Inositol Phosphate Formation in Primary Neuronal and Glial Cultures

alpha 1-Adrenergic receptor binding sites and norepinephrine-stimulated 3H-inositol phosphate (3H-InsP) accumulation were measured in primary cultures of neurons and glia from 1-day-old rat brains. The density of alpha 1-adrenergic receptor binding sites was approximately three times higher in membranes from neurons compared to glia. Although norepinephrine was slightly more potent in stimulating 3H-InsP formation in neurons than in glia, the maximal response was greater in glial cells. Norepinephrine-stimulated 3H-InsP formation remained constant for [3H]inositol prelabelling periods of 1-14 days in neurons, whereas the response increased with time in glia and was maximal after 7-10 days of prelabelling. Both the incorporation of [3H]inositol into lipid and basal levels of 3H-InsPs were lower in glial cells than in neurons, which accounted for the greater percent stimulation in glia. Pretreatment with phenoxybenzamine decreased norepinephrine-stimulated 3H-InsP formation in a dose-dependent manner in both neurons and glia by decreasing the maximal response without altering potency. HPLC separation showed that similar types of 3H-InsPs were accumulated in neurons and glial cells. These results demonstrate that alpha 1-adrenergic receptors exist on both neurons and glial cells and activate 3H-InsP accumulation in both cell types. Although receptor density is higher in neurons than in glia, the 3H-InsP response is higher in glia. This difference does not appear to be due to different receptor reserves, but may be due to differential coupling mechanisms in the two cell types.

Adrenergic status in anxiety disorders: Platelet alpha 2-adrenergic receptor binding, blood pressure, pulse, and plasma catecholamines in panic and generalized anxiety disorders patients and in normal subjects

In order to evaluate adrenergic function in anxiety disorders, platelet alpha 2-adrenergic binding parameters and supine and standing blood pressure, pulse, and venous plasma epinephrine and norepinephrine were determined in patients with panic attacks or generalized anxiety disorder and in normal subjects. The maximum number of binding sites (B max) for the partial agonist tritiated clonidine was significantly lower for both patient groups than for normal subjects, and the B max for the antagonist tritiated yohimbine was significantly lower for panic patients. There were no other substantive differences across groups. Prior exposure to psychotrophic drugs might account for the results for clonidine binding, but not for yphimbine. The B max for clonodine was correlated with norepinephrine increases upon standing and, for panic patients, with the severity of full unexpected panic attacks. These data provide further evidence of adrenergic receptor abnormalities in people with anxiety disorders.

Platelet alpha 2-adrenergic receptor binding to 3H-yohimbine and personality variations in normals

The authors examined platelet α 2-adrenergic receptor binding to 3H-yohimbine and several personality variables in 58 adult males in a campus community. Subjects with high receptor B max levels exhibited personality traits of less social inhibition and more sensation seeking and thrill seeking behavior, were more playful and autonomous, and came from healthier, more intact families. The results also suggested that high affinity states of platelet α 2-adrenergic receptors (low K d) correlate with traits suggestive of stability, i.e., Autonomy, Dominance, Nurturance, Order, Succorance, and General Sensation Seeking Scale of Zuckerman, while low affinity states (high K d) of platelet α 2-receptors correlate with psychopathological traits of Defendence, Exhibitionism, and Paranoia.

Autonomic Receptors in Human Prostate Adenomas

Radioligand receptor binding techniques were used to characterize alpha1 adrenergic, alpha2 adrenergic and muscarinic cholinergic (MCh) binding sites in human prostate adenomas obtained from men with symptomatic and asymptomatic benign prostatic hyperplasia (BPH). Prostate adenoma specimens were obtained from nine men with asymptomatic BPH undergoing cystoprostatectomy, 11 men with symptomatic BPH undergoing open prostatectomy, and 11 men with symptomatic BPH undergoing transurethral resection of the prostate (TURP). A quantitative symptoms score analysis and urinary flow rate determinations documented the absence of bladder outlet obstruction in men undergoing cystoprostatectomy and confirmed the presence of bladder outlet obstruction in men undergoing prostatectomy. The mean equilibrium dissociation constants (Kd) and the mean densities of 125I-Heat (alpha1 adrenergic) and 3H-NMS (MCh) binding sites were similar in tissue homogenates obtained from men with asymptomatic and symptomatic BPH. The mean Kd of 3H-Rauwolscine (3H-Ra) was significantly greater in the prostatectomy specimens obtained from men with symptomatic BPH compared to the specimens obtained from men with asymptomatic BPH (p < 0.05). The density of 3H-Ra (alpha2 adrenergic) binding sites was significantly greater in the prostate adenomas obtained from men with symptomatic BPH compared to the prostate adenomas obtained from men with asymptomatic BPH (p < 0.05). The difference in alpha2 adrenoceptor density was accounted for by an increased receptor density in the open prostatectomy specimens. There was no significant correlation between alpha2 adrenergic, alpha1 adrenergic, and MCh receptor densities and prostate weight or patient age. This study indicates that the development of infravesical obstruction in men with BPH is not related to upregulation or altered binding affinity of alpha1 adrenergic or MCh receptor binding sites. The significance of the observed upregulation of alpha2 adrenoreceptors in the prostate adenomas obtained from men undergoing open prostatectomy is unknown, and requires further investigation.

Renal nerve contribution to NaCl-exacerbated hypertension in spontaneously hypertensive rats.

Previous studies demonstrate that bilateral renal denervation enhances urinary sodium excretion and delays the onset of hypertension in young (7-week-old) spontaneously hypertensive rats (SHR) maintained on ordinary laboratory chow. We interpret these data as suggesting that increased renal nerve activity in this model contributes to hypertension by causing excess sodium retention. More recent studies show that dietary NaCl supplementation increases blood pressure and peripheral sympathetic nervous system activity in NaCl-sensitive SHR (SHR-S). The present study tests the hypothesis that the renal nerves contribute to the rise in arterial pressure caused by dietary NaCl supplementation in this model. SHR-S were fed a high (8%) or basal (1%) NaCl diet beginning at age 7 weeks. Bilateral renal denervation was carried out 2 weeks after the initiation of the diets, at which time systolic blood pressure was significantly higher in the high (compared with the basal) NaCl group. Systolic blood pressure was reduced slightly less in denervated SHR-S on the high (compared with basal) NaCl diet during the following 5 weeks. Renal denervation performed 1 week before initiation of the diets attenuated the subsequent development of hypertension equally in both groups. Both renal denervation and the high NaCl diet increased alpha 2-adrenergic receptor numbers in the kidney; renal denervation caused an approximately equal increase in alpha 2-adrenergic receptor binding in SHR-S on high and basal NaCl diets. The high NaCl diet increased plasma noradrenaline concentration, and renal denervation lowered mean arterial pressure but did not decrease circulating catecholamines in either diet group.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of Muscarinic Cholinergic and Alpha Adrenergic Receptors in Canine Ileum, Colon, Intestinal Urinary Reservoirs and Bladder

The muscarinic cholinergic (MCh) and alpha2 adrenergic receptor densities in canine ileum, colon, ileal and colonic urinary reservoirs and bladder were determined using radioligand receptor binding methods in order to provide a rational basis for pharmacologic management of urinary incontinence following bladder replacement with intestinal segments. Muscarinic cholinergic and alpha2 adrenergic receptor binding sites were studied in these tissues using saturation experiments with 3H-NMS and 3H-rauwolscine, respectively. The mean equilibrium dissociation constants for 3H-NMS binding (0.13 to 0.17nM) in these tissues were similar (p > 0.05) indicating homogeneity of muscarinic cholinergic binding sites. The mean equilibrium dissociation constants for 3H-rauwolscine binding (1.27 to 1.98nM) in these tissues were also similar (p > 0.05). A substantial density of MCh (1.06 to 1.22fmol/mg. wet wt.) and alpha2 adrenergic (0.47 to 1.11fmol/mg. wet wt.) binding sites was identified in the intestinal tissues assayed. The density of ileal and colonic MCh and alpha2 adrenergic binding sites was not altered following construction of urinary intestinal reservoirs. The presence of a substantial density of MCh and alpha2 adrenergic binding sites in the intestinal tissues suggests that MCh and alpha2 adrenergic analogs may be utilized for the management of urinary incontinence following bladder replacement with intestinal urinary reservoirs.

Platelet research in psychiatry.

The platelet is one of the most researched biological markers in psychiatry. Characteristics of MAO activity, 5-HT uptake, imipramine and alpha 2-adrenergic receptor binding, for example, are similar in platelet and CNS. Methodological factors are not negligible, and range from diagnostic specificity and drug effects to the normal physiological variability of age and hormone-related changes, circadian and seasonal rhythms. As yet, there are no clear state or trait platelet markers in affective disorders and schizophrenia that can be unequivocally used to detect vulnerability to the illness, predict therapeutic response, define clinical diagnostic entities or follow the course of the illness. However, platelet markers are increasingly being used in careful studies to monitor psychopharmacological effects (an in vivo assay of all active metabolites), different ligands can be specific markers for certain aspects of a psychiatric illness (e.g. alpha 2-adrenergic receptors and weight loss), and this homogeneous preparation of human cells is an increasingly important tool in studying mechanisms in pathophysiology. More longitudinal studies are required to establish functional relationships between platelet variables and psychopathology.

Neuropeptide y- and alpha-adrenergic receptors in pig spleen: Localization, binding characteristics, cyclic amp effects and functional responses in control and denervated animals

The localization of neuropeptide Y binding sites in the pig spleen, as revealed by [ 125I]Bolton-Hunter-labelled porcine neuropeptide Y and alpha 1-adrenergic receptor binding sites, as revealed by [ 125I](2-beta/4-hydroxy-phenyl/-ethylaminomethyl)-tetralone as radioligand, was compared with the distribution of neuropeptide Y and noradrenaline nerves, the latter revealed by tyrosine hydroxylase and dopamine-beta-hydroxylase, using immunohistochemistry. A large degree of codistribution was obtained between [ 125I]neuropeptide Y and alpha 1-binding sites in the capsule, trabeculae, blood vessels and the red pulp of the spleen. Neuropeptide Y and tyrosine hydroxylase as well as dopamine-beta-hydroxylase-positive nerves were identical in the spleen and had a similar gross distribution pattern as the [ 125I]neuropeptide Y and alpha 1 binding sites. In functional studies using the isolated blood-perfused spleen from pentobarbital-anaesthetized pigs, neuropeptide Y, noradrenaline and the alpha 1-selective agonist phenylephrine contracted the capsule and induced vasoconstriction in the spleen in vivo. However, the selective alpha 2-adrenoceptor agonists clonidine and azepexole had no effects on blood flow or perfusion pressure, suggesting that postjunctional alpha-receptors were of the alpha 1 type. Neuropeptide Y inhibited the forskolin-evoked, cyclic adenosine monophosphate formation in vitro. The [ 125I]neuropeptide Y binding, with an equilibrium-dissociation constant of 503 ± 73pM and a maximal number of specific binding sites of 23 ± 3fmol/mg protein, the neuropeptide Y-induced perfusion-pressure increase in vivo and the inhibition of forskolin-evoked cyclic adenosine monophosphate formation in vitro were dependent on the amidation of the C-terminal portion of the peptide molecule. Furthermore, the effects of neuropeptide Y were not changed by alpha- and beta-adrenoceptor blockade using prazosin and propranolol. Two weeks after postganglionic denervation the neuropeptide Y and the noradrenaline contents of the pig spleen were reduced by 97% and 99%, respectively. These changes were associated with a selective supersensitivity for the noradrenaline-induced perfusion-pressure increase in vivo compared with the effect of neuropeptide Y. However, a similar potentiation of the noradrenaline effect was induced by the monoamine-uptake blocker desipramine in the absence of denervation and there was no change in the functional response to phenylephrine after denervation. This indicated that the denervation supersensitivity for noradrenaline was of prejunctional rather than of postjunctional origin, although a significant increase in the maximal number of specific binding sites of the [ 3H]prazosin binding (75%) was observed in vitro. No significant changes in the equilibrium-dissociation constant or in the maximal number of specific binding sites were observed after denervation for the [ 125I]neuropeptide Y binding sites. Furthermore, the neuropeptide Y-induced inhibition of forskolin-induced cyclic adenosine monophosphate formation was not changed after denervation. It is concluded that alpha 1-adrenoceptor and neuropeptide Y binding sites are co-distributed and can be activated in parallel to induce muscle contraction in support of a co-transmitter role for noradrenaline and neuropeptide Y in the sympathetic nervous control of the pig spleen. Denervation was associated with a selective up-regulation of the alpha 1-adrenoceptor binding sites, but no changes in the binding characteristics were observed for neuropeptide Y, suggesting the absence of homeostatic responses in the regulation of neuropeptide Y receptors of the spleen.

Alpha-2 adrenergic receptor binding in platelets and brains of nervous and normal pointer dogs

Nervous pointer dogs have been suggested as an animal model for certain human pathological anxiety states. Work done in humans and in animals suggests a role for noradrenergic overactivity in the manifestations of anxiety. We studied α 2 adrenergic receptor binding as determined by [ 3H]-yohimbine in platelets and brains of the nervous and normal dogs in our colony. Our findings indicate that α 2 adrenergic receptor density and affinity are similar in platelets and frontal cortex, but we did not observe significant differences in binding between the two groups of dogs.

Differential regulation by butyrate and dibutyryl cyclic AMP of delta-opioid, alpha 2-adrenergic, and muscarinic cholinergic receptors in NCB-20 cells.

Long-term treatment of NCB-20 cells with sodium butyrate resulted in a marked increase in the specific binding of [3H]D-Ala2,D-Leu5 enkephalin. This increase was concentration and time dependent, with an EC50 of about 480 microM and a maximal effect detected after 3-day treatment. At saturating concentration of butyrate (1 mM) the increase was three- to fourfold of the untreated control. Scatchard analysis revealed that the butyrate effect was due to an increase in the density of the opioid receptor binding sites. Butyrate also induced a smaller (about twofold) increase in the density of muscarinic cholinergic receptor binding assessed by using [3H]quinuclidinyl benzilate, whereas alpha 2-adrenergic receptor binding assessed by using [3H]clonidine was not significantly affected. The butyrate-induced opioid receptor binding could be totally abolished by the presence of cycloheximide, suggesting that the butyrate effect involves synthesis of the receptor protein. Butyrate treatment did not affect basal and prostaglandin E1-stimulated cyclic AMP levels but caused a three- to fourfold decrease in the IC50 of D-Ala2,D-Leu5 enkephalin for attenuating these cyclic AMP levels and approximately 25% increase in the maximal extent of attenuation. In contrast to the butyrate effect, long-term treatment of NCB-20 cells with 1 mM dibutyryl cyclic AMP induced an 80% decrease in the opioid and alpha 2-adrenergic receptor bindings and a 57% loss of muscarinic cholinergic receptor binding. This down-regulation of muscarinic cholinergic receptor binding sites was associated with a 35% decrease of carbachol-induced phosphoinositide breakdown, whereas the receptor up-regulation induced by butyrate was found to increase the carbachol response by about threefold. The differential regulation by butyrate and dibutyryl cyclic AMP suggests that the butyrate effect is mediated by a mechanism independent of intracellular cyclic AMP. The induction by butyrate of opioid-receptors and muscarinic cholinergic receptors in NCB-20 cells may provide a useful system for studying the regulation of gene expression of these receptor proteins.

Comparison of the butyrate effects on neurotransmitter receptors in neurohybrids NG 108-15 and NCB-20 cells

Our previous study demonstrated that long term treatment of NCB-20 cells with sodium butyrate resulted in a marked increase in the density of delta-opioid receptors with a much lesser effect on muscarinic cholinergic and no effect on alpha 2-adrenergic receptors. In the present study we investigated the effect of sodium butyrate on these three types of receptors in NG108-15 cells whose neuroblastoma parent is the same as that of NCB-20 cells. Long term treatment of NG108-15 cells with sodium butyrate (0.5 nM) induced a 2-fold increase in the density of the specific binding of 3H-clonidine. A comparable increase in the number of binding sites was detected when 3H-yohimbine was used as the receptor ligand. The butyrate-induced increase in the alpha 2-adrenergic receptor binding could be totally abolished by treatment with a protein synthesis inhibitor, cycloheximide, suggesting that synthesis of receptor protein is involved. The same butyrate treatment had no significant effect on opioid and muscarinic cholinergic receptor bindings. Thus, butyrate effects on the expression of these types of receptors in NG108-15 and NCB-20 cells are dramatically different. These data suggest that induction by butyrate of neurotransmitter receptors requires concerted action of genetic factors of both parents of the neurohybrids.

Disparate effects of the calcium-channel blockers, nifedipine and verapamil, on alpha 2-adrenergic receptors and thromboxane A2-induced aggregation of human platelets.

Calcium-channel blockers inhibit human platelet aggregation in vitro and ex vivo. To further evaluate the mechanism(s) responsible for the inhibition induced by this structurally heterogeneous group of compounds, we studied the effect of nifedipine and verapamil on human platelet aggregation in vitro. Neither 10 microM nifedipine nor 10 microM verapamil consistently inhibited the aggregation response of platelet-rich plasma to threshold concentrations of ADP, sodium arachidonate, epinephrine, or collagen. However, both 10 microM nifedipine and 10 microM verapamil epinephrine-potentiated, thromboxane A2 (TXA2)-induced aggregation of aspirin-incubated, gel-filtered platelets. Aggregation of similarly prepared platelets induced by TXA2 alone was abolished by 10 microM nifedipine but not by 10 microM verapamil. Even 100 microM verapamil gave only partial and inconsistent inhibition of aggregation. Both drugs had essentially the same effects on platelet aggregation induced by the stable endoperoxide and TXA2 mimic, U46619, with or without epinephrine. Neither 10 microM nifedipine nor 10 microM verapamil elevated platelet cyclic AMP. Verapamil (10 microM) inhibited binding of [3H]-yohimbine (an alpha 2-adrenergic receptor antagonist) to intact human platelets (KD 10.5 nM vs 2.4 nM for control platelets) without altering the number of binding sites. In contrast, 10 microM nifedipine had no effect on KD or number of binding sites. These results indicate that nifedipine and verapamil inhibit epinephrine-potentiated, TXA2-induced human platelet aggregation by different mechanisms. Verapamil inhibits the epinephrine contribution to the aggregation response by blocking alpha 2-adrenergic receptor binding. Nifedipine blocks the platelet response to TXA2 without affecting alpha-adrenergic receptor binding. These observations have potential clinical implications with regard to the mechanisms by which calcium-channel blockers inhibit vascular spasm and myocardial ischemia.

Ascorbic acid inhibition of alpha-adrenergic receptor binding

Relatively low concentrations of ascorbic acid inhibited the binding of the alpha-1 adrenergic antagonist [ 125I]HEAT ( dl-[β(3-iodo-4-hydroxyphenyl)-ethyl-aminomethyl]-tetralone) in rat submandibular gland and rat aorta. However, no inhibition was observed with this ligand in several other tissues, nor with several other ligands in these tissues. The inhibition observed was dependent on the concentration of both the ascorbic acid and the tissue. Maximal inhibition of [ 125I]HEAT occurred in submandibular gland at 10 μM ascorbic acid with B max values reduced 65% and no change in affinity. Ascorbic acid had a greater effect in assays in which less tissue was used, causing a 22% decrease in binding at 46 μg/ml, but a 48% decrease in binding at a tissue concentration of 12 μg/ml. EDTA prevented the loss of binding normally seen with ascorbic acid at a tissue concentration of 17 μg/ml. We suggest that, if an antioxidant is thought to be necessary in an assay system, its effects be carefully examined before routine use.

Isolated adult cardiac myocytes as a model for alpha-adrenergic receptor binding studies

Isolated adult cardiac myocytes as a model for alpha-adrenergic receptor binding studies

DL-sodium lactate reduces alpha 1-adrenergic receptor binding in rat and mouse brain

DL-Sodium lactate decreases the density of α 1-adrenergic receptors in rat brain membranes in vitro, an effect that is not present for several other neuroreceptors under similar conditions. Moreover, similar effects on specific 3H-prazosin binding to α 1-adrenergic receptors can be seen in the mouse brain after intravenous (i.v.) administration of DL-sodium lactate. Since these effects can be observed with i.v. doses of DL-sodium lactate only slightly higher than the doses needed to provoke panic attacks in susceptible patients, it seems possible that similar changes in central neurotransmission might be involved in the biological mechanism underlying the induction of panic attacks by DL-sodium lactate.

Alpha 1-Adrenergic receptor binding in the spontaneously hypertensive rat.

Increased sympathetic outflow from the central nervous system to the periphery may contribute to the initiation of hypertension in spontaneously hypertensive rats (SHR). As this alteration in sympathetic activity may be mediated in part by alpha-adrenergic receptors in the central nervous system, the current study examined alpha 1-adrenergic receptors in various brain areas of SHR and normotensive Wistar-Kyoto control rats (WKY). The alpha 1-adrenergic receptor number and apparent affinity constants of brain sections of both young prehypertensive animals (4 weeks old) and mature hypertensive animals (12 weeks old) were studied with the alpha 1-adrenergic receptor antagonist [3H]WB-4101 to label the alpha-adrenergic receptor. Five brain regions were studied: rostral hypothalamus, caudal hypothalamus, locus ceruleus, nucleus tractus solitarius, and frontal cortical poles. In comparison to normotensive controls, mature hypertensive rats had a significantly greater density (p less than 0.05) of the alpha 1-adrenergic receptors in the rostral hypothalamus (+11%), caudal hypothalamus (+25%), and frontal cortical poles (+20%). Significantly greater (p less than 0.05) alpha 1-adrenergic receptor density was found in the rostral hypothalamus (+27%), caudal hypothalamus (+60%), and locus ceruleus (+39%) of the young prehypertensive SHR compared with age-matched WKY. These results indicate the presence of altered adrenergic receptor systems in the brains of genetically hypertensive animals and suggest that changes in the receptor systems take place during establishment of the hypertension.

Alpha 1-Adrenergic receptor binding in the spontaneously hypertensive rat.

alpha 1-Adrenergic receptor binding in the spontaneously hypertensive rat.

The effects of calcium antagonists on alpha-adrenergic receptor binding

The effects of calcium antagonists on alpha-adrenergic receptor binding

The effects of calcium antagonists on alpha-adrenergic receptor binding

The effects of calcium antagonists on alpha-adrenergic receptor binding