Biomedical subjects

D M Chuang

Publications and source records attributed to D M Chuang.

At least 109 records · Page 6Linked to original sources

PubMed1988

Changes in immunohistochemical properties of beta-adrenergic receptors in frog erythrocytes by isoproterenol-induced desensitization.

Immunohistochemical properties of beta-adrenergic receptor (BAR) in frog erythrocytes have been studied by using antiserum raised against purified guinea pig BAR. Immunoblotting of frog erythrocyte membranes with the anti-BAR serum revealed prominent staining of a protein with Mr of 65,000-67,000. BARs present in intact frog erythrocytes were made visible by incubation with the anti-BAR serum and then goat-anti rabbit IgG conjugated with colloidal gold. About 50-60% of the cells showed small, punctate dots by staining with the anti-BAR serum. After 4 hr exposure of the cells to isoproterenol, the density of the staining was markedly increased. Labeling of BAR after permeabilization of erythrocytes with saponin was markedly enhanced in isoproterenol-desensitized, but not in control cells. The BARs present in cytoslic fraction of desensitized cells migrated in the void volume of Sepharose-4B and were effectively labeled by a lipophilic BAR ligand capable of penetrating the cell membranes, but not by a hydrophilic ligand. Thus, isoproterenol-induced desensitization is associated with alteration of the immunoreactivity of BAR. Moreover, our immunochemical and biochemical data provide further evidence for the internalization of BAR in desensitized frog erythrocytes.

Animals↗

PubMed1988

Characterization of bradykinin-induced phosphoinositide turnover in neurohybrid NCB-20 cells.

Phosphoinositide hydrolysis was studied in neurohybrid NCB-20 cells prelabeled with myo-[3H]inositol. Among nearly 20 neurotransmitters and neuromodulators examined, only bradykinin, carbachol, and histamine significantly increased the accumulation of [3H]inositol monophosphate (IP1) in the presence of lithium. The EC50 of bradykinin was 20 nM and the saturating concentration was approximately 1 microM. The bradykinin response was robust (10-fold) and was potently and selectively blocked by a bradykinin antagonist, B 4881 [D-Arg-(Hyp3, Thi, D-Phe)-bradykinin], with a Ki of 10 nM. This effect of bradykinin appeared to be additive to that mediated by activation of muscarinic cholinergic and histamine H1 receptors. The accumulation induced by bradykinin or carbachol was dependent on the presence of calcium in the incubation medium; less than twofold stimulation was observed in the absence of exogenous calcium. Bradykinin-induced [3H]IP1 accumulation required high concentration of lithium to elicit its maximal stimulation; the concentration of lithium required for half maximal effect was about 13 mM, similar to the value reported previously for carbachol-induced accumulation in the same cell line. In contrast, using related neurohybrid NG108-15 cells, bradykinin-induced [3H]IP1 accumulation was found to require much less lithium. IN the presence of lithium, bradykinin also evoked a transient increase in the production of [3H]-inositol bis- and trisphosphate. Basal and bradykinin-induced phosphoinositide breakdown was inhibited by 4 beta-phorbol 12,13-dibutyrate, but was unaffected by the biologically inactive 4 beta-phorbol. Pretreatment of cells with pertussis toxin induced only about 30% loss of the bradykinin-induced [3H]IP1 accumulation, without affecting basal activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

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.

Alprostadil↗

PubMed1987

Modulation of calcium uptake and D-aspartate release by GABAB receptors in cultured cerebellar granule cells.

(-)Baclofen, a GABAB receptor agonist, and GABA attenuated by 60% the high K+-evoked 45Ca2+ uptake into cultured cerebellar granule cells with an EC50 of 110 +/- 18 nM and 2.4 +/- 0.2 microM, respectively. The attenuation by baclofen of 45Ca2+ uptake was stereospecific and the effect of GABA was unaffected by bicuculline. Moreover, muscimol, a GABAA receptor agonist did not affect the K+-evoked 45Ca2+ uptake. (-)Baclofen and GABA also decreased the K+-evoked and calcium-dependent release of preloaded [3H]D-aspartate from granule cells; however, their potency and efficacy appeared to be less than those for inhibiting the 45Ca2+ uptake. (+)Baclofen and muscimol failed to change this K+-evoked release. The release of [3H]D-aspartate induced by the calcium ionophore A23187 was unaffected by (-)-baclofen. The K+-evoked release of [3H]D-aspartate was effectively inhibited by nimodipine, a voltage sensitive calcium channel blocker. The results suggest that GABAB receptor in cultured cerebellar granule cells plays a crucial role in modulating the uptake of calcium and release of the excitatory transmitter. Moreover, these two effects mediated by GABAB receptor activation may be casually related.

Animals↗

PubMed1987

Multiple mechanisms of serotonergic signal transduction.

In this article we review serotonergic signal transduction mechanisms in the central and peripheral nervous systems and in a variety of target organs. The various classes of pharmacologically defined serotonergic receptors are coupled to three major effector systems: (1) adenylate cyclase; (2) phospholipase C mediated phosphoinositide (PI) hydrolysis and (3) ion channels (K+ and Ca++). Long term occupancy of serotonergic receptors also appears to induce alterations in mRNA and protein synthesis. For all three types of signal transduction there is evidence accumulating which suggests the involvement of guanine nucleotide regulatory proteins. Recent findings suggest that the distinct types of pharmacologically defined serotonergic receptors (5HT1A, 5HT1B, 5HT1c, 5HT2) may be coupled to one or more signal transduction systems. Thus, 5HT1 receptors may both activate and inhibit adenylate cyclase and increase K+-ion conductance in the hippocampus. 5HT2 receptors which activate PI hydrolysis in the brain, both open voltage-gated calcium channels and activate PI metabolism in certain smooth muscle preparations. Thus, each class of serotonergic receptor may be linked to one or more distinct biochemical transduction mechanisms. The possibility is raised that selective agonists and antagonists might be developed which have specific effects on a particular receptor-linked effector system.

Adenylyl Cyclases↗

PubMed1987

Comparison of the butyrate effects on neurotransmitter receptors in neurohybrids NG108-15 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 mM) 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 three 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.

Animals↗

PubMed1987

Serotonergic, adrenergic and histaminergic receptors coupled to phospholipase C in cultured cerebellar granule cells of rats.

Phosphatidylinositol (Ptdlns) turnover has been studied in the primary culture of granule cells dissociated from the cerebellum of postnatal rat. Addition of serotonin (5-hydroxytryptamine, 5-HT) caused an increase (300-600% of control) of [3H]inositol monophosphate (IP1) accumulation in the presence of LiCl in cells prelabeled with [3H]myo-inositol. The EC50 and saturation concentrations of 5-HT were about 0.1 and 10 microM respectively. Some nonselective 5-HT receptor agonists, MK212, 5-methoxytryptamine, tryptamine and quipazine, were capable of stimulating IP1 accumulation; a selective 5-HT1A receptor agonist, 8-OH-DPAT, was ineffective. The 5-HT-induced response was potently blocked by several 5-HT2 receptor antagonists such as ketanserin, mianserin, spiroperidol and pyzotyline. The 5-HT-induced accumulation was dependent on the culturing time of granule cells with the maximal response seen in an 8-day culture. Norepinephrine (NE) also promoted an increased IP1 accumulation (300% of the control) with an EC50 of about 1 microM, while prazosin inhibited this NE-induced response with a Ki of about 0.2 nM. The responses induced by NE and 5-HT appeared to be additive. In addition, histamine in a dose-dependent manner enhanced the accumulation by about 100%; this histamine effect was blocked by triprolidine, an H1 receptor antagonist, but not by cimetidine, an H2 receptor antagonist. These results suggest that 5-HT, NE and histamine could be part of the neurotransmitter substances present in mossy fibers or other afferent nerve endings which innervate granule cells in vivo and that Ptdlns turnover regulated by their selective receptors on granule cells may play a role in modulating the excitatory function of these neurons.

Animals↗

PubMed1987

Characterization of two [3H]ketanserin recognition sites in rat striatum.

Two [3H]ketanserin recognition sites are present in the rat striatum. The high-affinity site (KD, 0.39 nM) is similar to the 5-hydroxytryptamine2 (5-HT2) site previously characterized by various investigators. The low-affinity site (KD, 21.8 nM) has a unique pharmacologic specificity and is preferentially localized to rat striatum and septum. Conventional 5-HT2 antagonists as well as 5-HT and 5-HT uptake inhibitors are ineffective at inhibiting [3H]-ketanserin binding to this low-affinity site. Also, chronic treatment with p-chlorophenylalanine, which depletes brain 5-HT, upregulates only the high-affinity site. Thus, in the striatum and septum, [3H]ketanserin labels a unique recognition site. This site has recently been shown to be associated with dopaminergic nerve endings and may regulate biogenic amine release.

Animals↗

PubMed1987

Muscarinic acetylcholine receptor-mediated phosphoinositide turnover in cultured cerebellar granule cells: desensitization by receptor agonists.

Cultured granule cells prepared from 8-day postnatal rats were used for the study of carbachol-induced phosphoinositide turnover. The addition of carbachol induced a 20- to 30-fold increase in [3H]inositol monophosphate (IP1) accumulation within 30 min in the presence of 20 mM LiCl in granule cells prelabeled with [3H]myoinositol. Carbachol also stimulated the formation of [3H]inositol bisphosphate and [3H]inositol trisphosphate assayed either in the presence or in the absence of lithium; the increase in [3H]inositol triphosphate and [3H]inositol biphosphate synthesis appeared to be faster in the time course but much smaller in amount when compared with the formation of [3H]IP1. The EC50 of carbachol was approximately 7 microM, and the saturation concentration was about 100 microM. This carbachol-induced response was completely blocked by two muscarinic acetylcholine receptor (mAChR) antagonists, atropine and pirenzepine, with a Ki of 0.5 and 120 nM, respectively. Saturation studies of the binding of [3H]N-methylscopolamine and [3H]quinuclidinyl benzilate to mAChRs in intact granule cells revealed the presence of a single class of binding sites with a Kd of 140 and 126 pM, respectively, and a Bmax of approximately 70 fmol/10(6) cells for both ligands. Within 1 hr after pre-exposure of cells to carbachol, the subsequent carbachol-induced [3H]IP1 accumulation was reduced by about 50%, whereas mAChR binding, assessed by using either [3H]N-methylscopolamine or [3H]quinuclidinyl benzilate, was unchanged. A second slower phase of desensitization was associated with a loss of mAChR binding sites; at 18 hr, the decrease of responsiveness was about 80%, whereas the loss of mAChR sites was about 60%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Carbachol-induced accumulation of inositol-1-phosphate in neurohybridoma NCB-20 cells: effects of lithium and phorbol esters.

Clonal neurohybridoma NCB-20 cells expressed muscarinic cholinergic receptors coupled to phospholipase C. Addition of carbachol in the presence of Li+ to cells prelabeled with 3H-inositol increased 3H-inositol-l-phosphate (3H-IP1) accumulation by more than 4-fold with an EC50 of about 50 microM. This carbachol-induced response was blocked by atropine and pirenzepine with a Ki of 0.5 and 25 nM, respectively. The EC50 of Li+ for the carbachol-induced phosphoinositide turnover was 17 +/- 1.2 mM compared with a value of 1.8 +/- 0.2 mM in brain slices, suggesting the presence of an unusual type of inositol-l-phosphatase in NCB-20 cells. Carbachol-induced IP1 accumulation in these cells was potently and noncompetitively inhibited by the biologically active phorbol esters, phorbol dibutyrate (PDB) and phorbol myristate diacetate (PMA), while the biologically inactive phorbol, 4 beta-phorbol, failed to affect this phosphoinositide breakdown. The basal IP1 accumulation was also significantly attenuated by PDB and PMA but not by 4 beta-phorbol.

Animals↗

PubMed1986

Coupling of inositol phospholipid metabolism with excitatory amino acid recognition sites in rat hippocampus.

Ibotenate, a rigid structural analogue of glutamate, markedly enhances the hydrolysis of membrane inositol phospholipids, as reflected by the stimulation of [3H]inositol monophosphate formation in rat hippocampal slices prelabeled with [3H]inositol and treated with Li+. Quisqualate, homocysteate, L-glutamate, and L-aspartate also induce a significant (albeit weaker) increase in [3H]inositol monophosphate formation, whereas N-methyl-D-aspartate, kainate, quinolinate, and N-acetylaspartylglutamate are inactive. The increase in [3H]inositol monophosphate formation elicited by the above-mentioned excitatory amino acids is potently and selectively antagonized by DL-2-amino-4-phosphonobutyric acid, a dicarboxylic amino acid receptor antagonist. These results suggest that, in the hippocampus, a class of dicarboxylic amino acid recognition sites is coupled with phospholipase C, the enzyme that catalyzes the hydrolysis of membrane inositol phospholipids.

Animals↗

PubMed1986

5-Hydroxytryptamine2 receptors coupled to phospholipase C in rat aorta: modulation of phosphoinositide turnover by phorbol ester.

In rat aorta, 5-hydroxytryptamine (5-HT) stimulated phosphoinositide (PI) turnover and contraction (EC50 = 10 +/- 3 microM); these two responses were highly correlated (r = 0.95; P less than .01). We have characterized the inhibitory potency of a variety of 5-HT-antagonists against the stimulation of PI turnover elicited by 5-HT. Classic 5-HT2 antagonists mianserin, ketanserin, metergoline and pizotifen were found to inhibit this response in the low nanomolar range; amitryptiline and haloperidol were 10- to 20-fold less potent. The alpha-1 receptor antagonist, prazosin, was inactive in micromolar concentrations. The potency of the 5-HT2 antagonists was correlated with their ability to displace [3H] ketanserin binding from rat frontal cortex membranes (r = 0.90; P less than .05). The tumor promoter phorbol dibutyrate was found to inhibit 5-HT-stimulated PI turnover at low nanomolar concentrations whereas the biologically inactive substance 4-alpha-phorbol was ineffective. Pretreatment of rat aorta with phorbol dibutyrate at concentrations that inhibited 5-HT-induced PI turnover also attenuated the aortic contraction induced by 5-HT in the presence of a calcium channel blocker nitrendipine. Our results suggest that phorbol esters may desensitize 5-HT2-receptor-mediated PI turnover and contraction of rat aorta, possibly via an activation of protein kinase C.

Animals↗

PubMed1986

Detection and characterization of beta-adrenergic receptors and adenylate cyclase in coated vesicles isolated from bovine brain.

To assess whether internalization of beta-adrenergic receptor occurs in the CNS, we have isolated clathrin-coated vesicles from bovine forebrain and examined them for the presence of beta-adrenergic receptor binding and adenylate cyclase activities. A coated vesicle enriched preparation isolated by successive D2O-Ficoll density gradient centrifugations was applied to a glass bead permeation column to achieve further purification. Two major peaks of protein were eluted from the column and monitored by electron microscopy and SDS-PAGE. Peak II contained almost exclusively coated vesicles (98%), whereas peak I, which appeared in the void volume, contained larger smooth vesicles and few coated vesicles. beta-Adrenergic receptor binding to peaks I and II was measured with 125I-cyanopindolol (CYP) as ligand in Sepharose 4B column assays. 125I-CYP was found to bind specifically and saturably to both peaks I and II with a Bmax of 28 +/- 4 and 32 +/- 3 fmol/mg protein, respectively. 3H-CGP 12177, a hydrophilic beta-adrenergic receptor ligand, did not label receptors present in peak II, but it specifically bound to synaptic plasma membranes (SPM) prepared from bovine hippocampus and, to a lesser extent, to peak I. These results suggest that receptors present in coated vesicles are cryptic in nature. In the displacement of 125I-CYP binding by (-)-isoproterenol, addition of 50 microM GppNHp caused a significant "right shift" with SPM and peak I but not the peak II preparation. Adenylate cyclase activities could also be detected in both peaks I and II (specific activities, 21 +/- 0.6 and 24 +/- 0.5 pmol cAMP/mg protein/min, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗

PubMed1985

5-Hydroxytryptamine uptake and imipramine binding sites in neurotumor NCB-20 cells.

NCB-20 cells (neuroblastoma X fetal Chinese hamster brain hybrids) are equipped with a [3H]5-hydroxytryptamine [( 3H]5-HT) uptake system and [3H]imipramine recognition sites. Approximately 80% of the radioactivity taken up by cells incubated with [3H]5-HT was identified with 5-HT. [3H]5-HT uptake was temperature-dependent, partially sodium-dependent, saturable (Km = 7.3 +/- 0.6 microM; Vmax = 2.0 +/- 0.6 pmol/min/mg), and inhibited by clomipramine, imipramine, fluoxetine, and desipramine, but not by iprindole, mianserin, or opipramol. Lineweaver-Burk plots showed a competitive type of inhibition by imipramine and fluoxetine. [3H]5-HT uptake was not inhibited by nisoxetine or benztropine. [3H]Imipramine binding sites had a KD of 12 +/- 2 nM and a Bmax of 22 +/- 7 pmol/mg protein. The binding was sodium-sensitive although to a lesser extent than that found with brain membranes. Imipramine binding was displaced by tricyclic antidepressants with the following order of potency: clomipramine greater than imipramine greater than fluoxetine greater than desipramine much greater than iprindole = mianserin greater than opipramol. These results suggest that imipramine binding sites are present together with the 5-HT uptake sites in NCB-20 cells and that these sites interact functionally but are different biochemically.

Animals↗

PubMed1985

Phasic and tonic components in 5-HT2 receptor-mediated rat aorta contraction: participation of Ca++ channels and phospholipase C.

The mechanisms of 5-hydroxytryptamine (5-HT)-induced contraction of rat aorta were investigated in vitro. The 5-HT-induced contraction could be analyzed into two distinct components (phasic and tonic) by the use of appropriate inhibitors; nifedipine, an inhibitor of voltage-dependent Ca++ channels, inhibited only the phasic component of 5-HT-induced contraction while totally blocking the KCl-induced contraction. 2-Nitro-4-carboxyphenyl-N,N-diphenylcarbamate, an inhibitor of phospholipase C, inhibited the tonic components of 5-HT-induced contraction as well as the 5-HT-induced stimulation of phosphoinositide hydrolysis in rat aorta. This component of contraction was mimicked by a protein kinase C activator 12-O-tetradecanoylphorbol-13-acetate. These results suggest that 5-HT2 receptors differentially regulate a voltage-dependent Ca++ channel and phospholipase C activity; the voltage-dependent Ca++ channel is involved in the phasic component of contraction whereas the phosphoinositide hydrolysis that results in the activation of protein kinase C and calcium mobilization by inositol triphosphate plays a physiologically important role in the tonic component of the aortic contraction.

Animals↗

PubMed1985

Benzodiazepines enhance the muscimol-dependent activation of phospholipase A2 in glioma C6 cells.

Glioma C6 cells were incubated with [14C]arachidonate to label membrane phospholipids. Muscimol, a selective gamma-aminobutyric acid A receptor agonist, but not (-)-baclofen, a selective gamma-aminobutyric acid B receptor agonist, stimulates [14C]arachidonate release from C6 cells as a result of hydrolysis of a small pool of phosphatidylcholine and phosphatidylethanolamine by phospholipase A2. This release is facilitated by diazepam and a number of other benzodiazepines such as flunitrazepam, medazepam and midazolam (but very little by clonazepam), although these benzodiazepines per se are inactive in causing the release. In addition to increasing the release of [14C]arachidonate, diazepam in the presence of muscimol promotes the release of [14C] prostaglandin D2. Bicuculline inhibits the action of muscimol and facilitation by diazepam. "Peripheral" benzodiazepine ligand, RO 5-4864 (4'-chlordiazepam) antagonizes the action of diazepam, whereas "central" ligand, RO 15-1788, is inactive. The release of arachidonate metabolites stimulated by muscimol and diazepam is unaffected by Cl- channel blockers, picrotoxin and pentylenetetrazol. Based on these results we propose that in glioma C6 cells (and presumably in normal glia) peripheral benzodiazepine receptor interacts functionally with gamma-aminobutyric acid A type of receptor, which appears not to be linked to picrotoxin sensitive Cl- channel, and may be linked to phospholipase A2.

Animals↗

PubMed1985

A monoclonal antibody to a membrane component that interacts with the beta-adrenergic receptor.

A monoclonal antibody has been obtained using a combination of in vivo and in vitro immunization with a digitonin extract of purified plasma membranes from frog erythrocytes. This antibody was found to immunoprecipitate a fraction of solubilized beta-adrenergic receptor (labeled with 125I-iodohydroxybenzylpindolol) derived from frog erythrocytes and a few other sources. This immunoglobulin also significantly activated adenylate cyclase in isolated erythrocyte plasma membranes measured in the presence of GTP or GTP plus isoproterenol. Immunoprecipitation of labeled erythrocyte surface proteins and immunoblotting of the digitonin-extract of erythrocyte plasma membrane revealed that the antibody interacted with a protein with a Mr = 43,000 and pI = 6.2 32P-ADP-ribosylated alpha subunit of Ns (with Mr = 44,000) solubilized from frog erythrocyte membranes failed to be immunoprecipitated by the antibody. Thus the antigenic protein is distinct from the beta-adrenergic binding site and alpha subunit of Ns and therefore may be an unidentified component of the beta-adrenergic receptor-adenylate cyclase system. This monoclonal antibody may be a useful tool for future studies for topological and functional interactions between the beta-adrenergic receptor and other membrane components.

Adenylyl Cyclases↗

PubMed1985

Evidence for an endacoid for the 5HT2 recognition site.

A peptide was partially purified from bovine forebrain which specifically inhibits the binding of [3H]-ketanserin to the 5HT2 recognition site. The peptide has a MW of approximately 6,000 daltons and is partially destroyed by limited proteolysis. We suggest that the peptide is a candidate for an endacoid for the 5HT2 recognition site.

Animals↗