RESUMEN
PURPOSE: Hot flashes occur in approximately 80% of androgen-deprived men. Few intervention studies have been conducted to relieve hot flashes in men. PATIENTS AND METHODS: Eligible androgen-deprived men were randomly assigned to one of four daily regimens (2 × 2 factorial design) for 12 weeks: milk protein powder and placebo pill, venlafaxine and milk protein powder, soy protein powder and placebo pill, or venlafaxine and soy protein powder. The primary end point was hot flash symptom severity score (HFSSS), defined as number of hot flashes times severity. The secondary end point was quality of life (QoL), assessed by using the Functional Assessment of Cancer Therapy-Prostate. RESULTS: In all, 120 men age 46 to 91 years participated. Most were white (78%) and overweight or obese (83%). Toxicity was minimal. Neither venlafaxine nor soy protein alone or in combination had a significant effect on HFSSS. Soy protein, but not venlafaxine, improved measures of QoL. CONCLUSION: In androgen-deprived men, neither venlafaxine nor soy proved effective in reducing hot flashes. Interventions that appear effective for decreasing hot flashes in women may not always turn out to be effective in men.
Asunto(s)
Antagonistas de Andrógenos/efectos adversos , Ciclohexanoles/uso terapéutico , Sofocos/prevención & control , Neoplasias de la Próstata/tratamiento farmacológico , Inhibidores Selectivos de la Recaptación de Serotonina/uso terapéutico , Proteínas de Soja/uso terapéutico , Anciano , Anciano de 80 o más Años , Método Doble Ciego , Sofocos/etiología , Humanos , Masculino , Persona de Mediana Edad , Calidad de Vida , Clorhidrato de VenlafaxinaRESUMEN
This paper examines the influence of the Berlin model on psychoanalytic education in New York through the person of Sandor Rado, who was recruited from Berlin to become the first Education Director at the New York Psychoanalytic Institute in 1931, and later went on to found the Columbia University Center for Psychoanalytic Training and Research. While the basic elements of the so-called tripartite model of psychoanalytic education were adopted in principle in New York prior to Rado's arrival, he had an enormous impact on the development and implementation of that curriculum, while attempting to modify it both theoretically and clinically, and became one of the focal points of the controversies that led to the break-up of that institute. He also sought to expand ties to American medicine and psychiatry and to research in general.
Asunto(s)
Curriculum , Educación , Métodos , Psicoanálisis , Investigadores , Enseñanza , Academias e Institutos/historia , Berlin/etnología , Educación/historia , Docentes/historia , Historia del Siglo XX , Ciudad de Nueva York/etnología , Psicoanálisis/educación , Psicoanálisis/historia , Teoría Psicoanalítica , Investigadores/educación , Investigadores/historia , Investigadores/psicología , Enseñanza/historiaRESUMEN
BACKGROUND: P2Y(12) plays an important role in regulating platelet aggregation and function. This receptor is the primary target of thienopyridine antiplatelet agents, the active metabolites of which bind irreversibly to the receptor, and of newer agents that can directly and reversibly modulate receptor activity. OBJECTIVE: To characterize the receptor biology of the first reversibly binding oral P2Y(12) antagonist, ticagrelor (AZD6140), a member of the new cyclopentyltriazolopyrimidine (CPTP) class currently in phase III development. METHODS: Ticagrelor displayed apparent non-competitive or insurmountable antagonism of ADP-induced aggregation in human washed platelets. This was investigated using competition binding against [(3)H]ADP, [(33)P]2MeS-ADP and the investigational CPTP compound [(125)I]AZ11931285 at recombinant human P2Y(12). Functional receptor inhibition studies were performed using a GTPgammaS-binding assay, and further binding studies were performed using membranes prepared from washed human platelets. RESULTS: Radioligand-binding studies demonstrated that ticagrelor binds potently and reversibly to human P2Y(12) with K(on) and K(off) of (1.1 +/- 0.2) x 10(-4) nm(-1) s(-1) and (8.7 +/- 1.4) x 10(-4) s(-1), respectively. Ticagrelor does not displace [(3)H]ADP from the receptor (K(i) > 10 mum) but binds competitively with [(33)P]2MeS-ADP (K(i) = 4.3 +/- 1.3 nm) and [(125)I]AZ11931285 (K(i) = 0.33 +/- 0.04 nm), and shows apparent non-competitive inhibition of ADP-induced signaling but competitive inhibition of 2MeS-ADP-induced signaling. Binding studies on membranes prepared from human washed platelets demonstrated similar non-competitive binding for ADP and ticagrelor. CONCLUSIONS: These data indicate that P2Y(12) is targeted by ticagrelor via a mechanism that is non-competitive with ADP, suggesting the existence of an independent receptor-binding site for CPTPs.
Asunto(s)
Adenosina Difosfato/química , Adenosina/análogos & derivados , Agregación Plaquetaria/efectos de los fármacos , Receptores Purinérgicos P2/metabolismo , Adenosina/química , Adenosina/farmacología , Animales , Sitios de Unión , Plaquetas/metabolismo , Células CHO , Membrana Celular/metabolismo , Cricetinae , Cricetulus , Humanos , Cinética , Unión Proteica , Pirimidinas/farmacología , Receptores Purinérgicos P2Y12 , Transducción de Señal , TicagrelorRESUMEN
P2Y receptor activation in many cell types leads to phospholipase C activation and accumulation of inositol phosphates, while in blood platelets, C6-2B glioma cells, and in B10 microvascular endothelial cells a P2Y receptor subtype, which couples to inhibition of adenylyl cyclase, historically termed P2Y(AC), (P2T(AC) or P(2T) in platelets) has been identified. Recently, this receptor has been cloned and designated P2Y(12) in keeping with current P2 receptor nomenclature. Three selective P(2T) receptor antagonists, with a range of affinities, inhibited ADP-induced aggregation of washed human or rat platelets, in a concentration-dependent manner, with a rank order of antagonist potency (pIC(50), human: rat) of AR-C78511 (8.5 : 9.1)>AR-C69581 (6.2 : 6.0)>AR-C70300 (5.4 : 5.1). However, these compounds had no effect on ADP-induced platelet shape change. All three antagonists had no significant effect on the ADP-induced inositol phosphate formation in 1321N1 astrocytoma cells stably expressing the P2Y(1) receptor, when used at concentrations that inhibit platelet aggregation. These antagonists also blocked ADP-induced inhibition of adenylyl cyclase in rat platelets and C6-2B cells with identical rank orders of potency and overlapping concentration - response curves. RT - PCR and nucleotide sequence analyses revealed that the C6-2B cells express the P2Y(12) mRNA. These data demonstrate that the P2Y(AC) receptor in C6-2B cells is pharmacologically identical to the P2T(AC) receptor in rat platelets.
Asunto(s)
Plaquetas/metabolismo , Glioma/metabolismo , Proteínas de la Membrana , Receptores Purinérgicos P2/metabolismo , Adenosina Difosfato/farmacología , Animales , Plaquetas/efectos de los fármacos , AMP Cíclico/metabolismo , Masculino , Agregación Plaquetaria/efectos de los fármacos , Antagonistas del Receptor Purinérgico P2 , ARN Mensajero/efectos de los fármacos , ARN Mensajero/metabolismo , Ratas , Ratas Sprague-Dawley , Receptores Purinérgicos P2/efectos de los fármacos , Receptores Purinérgicos P2/genética , Receptores Purinérgicos P2Y1 , Receptores Purinérgicos P2Y12 , Células Tumorales CultivadasRESUMEN
P2X4 receptors are expressed in specific brain areas. We now describe site-specific splice variations of the human P2X4 receptor subunit, occurring at residue [YVIG / WVFV(W)] near the end of the first predicted transmembrane domain. p2X4(b) is formed by the insertion of an additional 16 amino acids. p2X4(C) is formed by deleting a cassette of 130 amino acids, including six of the 10 conserved extracellular cysteine residues. Transfection of P2X4(a), but not p2x4(c), formed functional channels in Xenopus oocytes and human 1321N1 cells. After transfection of p2X4(b) small, inconsistent ATP-evoked responses were detected only in the human cells, but when co-expressed, p2x4(b) may alter the function of P2X4(a) in oocytes. The distribution of splice variant RNA within human brain suggests regionally-dependent expression. These data indicate that the functions of the human P2X4 receptor may be altered by alternative splicing.
Asunto(s)
Empalme Alternativo/genética , Neuropéptidos/genética , Receptores Purinérgicos P2/genética , Adenosina Trifosfato/farmacología , Empalme Alternativo/efectos de los fármacos , Secuencia de Aminoácidos/genética , Animales , Células Cultivadas , ADN/genética , Humanos , Datos de Secuencia Molecular , Neuropéptidos/efectos de los fármacos , Neuropéptidos/metabolismo , Oocitos , Receptores Purinérgicos P2/efectos de los fármacos , Receptores Purinérgicos P2/metabolismo , Receptores Purinérgicos P2X4 , Transfección/genética , XenopusRESUMEN
The platelet P2T receptor plays a major role in platelet aggregation, and its antagonists are predicted to have significant therapeutic potential as antithrombotic agents. We have explored analogues of adenosine triphosphate (ATP), which is a weak, nonselective but competitive P2T receptor antagonist. Modification of the polyphosphate side chain to prevent breakdown to the agonist adenosine diphosphate (ADP) and substitution of the adenine moiety to enhance affinity and selectivity for the P2T receptor led to the identification of 10e (AR-C67085MX), having an IC50 of 2.5 nM against ADP-induced aggregation of human platelets. Compound 10e was the first very potent antagonist of the P2T receptor, with a selectivity for that subtype of the P2 receptor family of >1000-fold. Further modification of the structure produced compound 10l (AR-C69931MX) having an IC50 of 0.4 nM. In vivo, at maximally effective antithrombotic doses, there is little prolongation of bleeding time (1.4-fold), which is in marked contrast to the 5-6-fold found with GPIIb/IIIa antagonists.
Asunto(s)
Adenosina Monofosfato/análogos & derivados , Plaquetas/efectos de los fármacos , Proteínas de la Membrana , Inhibidores de Agregación Plaquetaria/farmacología , Antagonistas del Receptor Purinérgico P2 , Trombosis/tratamiento farmacológico , Adenosina Monofosfato/química , Adenosina Monofosfato/farmacología , Adenosina Monofosfato/uso terapéutico , Plaquetas/metabolismo , Humanos , Espectroscopía de Resonancia Magnética , Estructura Molecular , Inhibidores de Agregación Plaquetaria/química , Inhibidores de Agregación Plaquetaria/uso terapéutico , Receptores Purinérgicos P2Y12 , Espectrometría de Masa Bombardeada por Átomos VelocesRESUMEN
The determination of octanol-water partition coefficients (log K(ow)) is important for the prediction of the fate of organic pollutants in the environment. Traditionally, log K(ow) values are determined by shake-flask, estimated by, e.g., HPLC retention data, or calculated, e.g., from ClogP. In this paper, an alternative approach is reported that allows log K(ow) to be estimated from solid-phase microextraction (SPME) data. Previously reported attempts to correlate SPME data with log K(ow) are discussed. The results obtained in this work for six phenols, using an 85 µm polyacrylate-coated fiber, indicate that SPME is a viable method for estimating log K(ow) values <3.5.
RESUMEN
1. The role of endogenous ADP in platelet aggregation in vivo remains unclear due to the lack of suitable P2T-antagonist probes. This paper describes the potency, selectivity and specificity of the novel P 2T-purinoceptor antagonist, FPL 67085 (2-propylthio-D-beta,gamma-dichloromethylene ATP) both in vitro and in the anaesthetized rat in vivo. 2. FPL 67085 (3-30 nM) produced concentration-dependent rightward displacement of the concentration-effect (E/[A]) curve for ADP-induced aggregation of human washed platelets with no effect on ADP-independent aggregation at < or = 10 microM. 3. Logistic fitting of ADP E/[A] data indicated that the antagonist effect of FPL 67085 did not consistently accord with simple competition: in some preparations depression of the asymptote was seen. Schild analysis of data combined from all preparations, regardless of the antagonist profile observed, gave an apparent pKB of 8.9 (slope parameter 0.90). 4. The potency of FPL 67085 was unaffected by the P1-purinoceptor antagonist, 8-sulphophenyltheophylline, was similar (IC50 0.6-3.8 nM) in human and rat washed platelets or whole blood and, in rat blood, did not change following 2-30 min incubation at 37 degrees C. 5. FPL 67085 was a weak (pA50 approximately 4.2) partial agonist in tissues containing P2X- or P2Y-purinoceptors, indicating some 30,000 fold selectivity for the P2T-subtype. 6. In anaesthetized rats, intravenous infusion of FPL 67085 produced rapidly-reversible, dose-related inhibition of ADP-induced platelet aggregation measured ex vivo (ID50 1.3 micrograms kg-1 min-1) with no significant effect on haemodynamics or circulating cell counts. 7. Thus, FPL 67085 is a potent, specific and selective inhibitor of ADP-induced platelet aggregation both in vitro and in vivo. As such, it represents a novel pharmacological tool to define the role of endogenous ADP in thrombosis and the potential of P2T-purinoceptor antagonists as a novel class of infusible anti-thrombotic agents for acute use in man.
Asunto(s)
Adenosina Difosfato/farmacología , Adenosina Trifosfato/análogos & derivados , Antagonistas del Receptor Purinérgico P2 , Adenosina Trifosfato/farmacología , Anestesia , Animales , Aorta/efectos de los fármacos , Arterias/efectos de los fármacos , Plaquetas/efectos de los fármacos , Presión Sanguínea/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Femenino , Cobayas , Frecuencia Cardíaca/efectos de los fármacos , Humanos , Técnicas In Vitro , Masculino , Conejos , Ratas , Ratas Sprague-Dawley , Receptores Purinérgicos P2/efectos de los fármacosRESUMEN
1. ADP-dependent platelet aggregation is mediated by the P2T-purinoceptor and is specifically inhibited by ATP, which is a competitive P2T-purinoceptor antagonist. However, ATP functions as an agonist at other P2-purinoceptor subtypes in other tissues and is, therefore, non-selective. This paper describes the effects of the novel ATP analogue, FPL 66096 (2-propylthio-D-beta,gamma-difluoromethylene ATP), on ADP-induced and ADP-independent aggregation of human washed platelets and in standard preparations containing P2X- (rabbit ear artery) and P2Y-purinoceptors (guinea-pig aorta). 2. In suspensions of human washed platelets, FPL 66096 (1-100 nM) produced concentration-dependent rightward displacement of concentration-effect (E/[A]) curves obtained for ADP-induced platelet aggregation. Logistic fitting of E/[A] data indicated that the effect of FPL 66096 was consistent with simple competition with a pKB value of 8.66. FPL 66096 (10-1000 nM) had no effect on aggregation produced by the thromboxane A2-mimetic, U46619 (0.1-10 microM) when the response to this agent was rendered ADP-independent by inclusion of the non-selective P2-purinoceptor antagonist, suramin (100 microM). 3. The anti-aggregatory potency of FPL 66096 was not influenced by increasing the incubation time from 2 to 15 min nor by inclusion of the P1-purinoceptor antagonist 8-sulphophenyltheophylline at a concentration (300 microM) that produced a 68 fold rightward displacement of the anti-aggregatory E/[A] curve for the P1-purinoceptor agonist, 5'-N-ethylcarboxamidoadenosine (0.1-1000 microM). 4. FLP 66096 behaved as a weak (pA" 3.68) but full P2x-purinoceptor agonist in preparations of the rabbit isolated ear artery and as a weak, competitive antagonist (apparent pKB 4.71) at P2Y purinoceptors in the guinea-pig isolated aorta, indicating a selectivity of at least 9000 fold for the P2t-subtype. In the latter preparation, non-specific relaxations were produced by concentrations of FPL 66096 >10M gM.5. These results indicate that FPL 66096 is a P2-purinoceptor antagonist of unprecedented potency and selectivity and that its effects are consistent with simple competition at the P2-purinoceptor. Therefore,FPL 66096 represents a novel pharmacological tool in the classification of P2-purinoceptors and in the elucidation of the mechanisms involved in activation of platelets by ADP.
Asunto(s)
Adenosina Trifosfato/análogos & derivados , Inhibidores de Agregación Plaquetaria/farmacología , Antagonistas del Receptor Purinérgico P2 , Adenosina Difosfato/farmacología , Adenosina Trifosfato/farmacología , Animales , Cobayas , Humanos , Técnicas In Vitro , Masculino , Agregación Plaquetaria/efectos de los fármacos , Conejos , Teofilina/análogos & derivados , Teofilina/farmacología , Tionucleótidos/farmacologíaRESUMEN
Calcium entry into excitable cells through voltage-gated calcium channels can be influenced by both the rate and pattern of action potentials. We report here that a cloned neuronal alpha 1C L-type calcium channel can be facilitated by positive pre-depolarization. Both calcium and barium were effective as charge carriers in eliciting voltage-dependent facilitation. The induction of facilitation was shown to be independent of intracellular calcium levels, G-protein interaction and the level of phosphatase activity. Facilitation was reduced by the injection of inhibitors of protein kinase A and required the coexpression of a calcium channel beta subunit. In contrast, three neuronal non-L-type calcium channels, alpha 1A, alpha 1B and alpha 1E, were not subject to voltage-dependent facilitation when coexpressed with a beta subunit. The results indicate that the mechanism of neuronal L-type calcium channel facilitation involves the interaction of alpha 1 and beta subunits and is dependent on protein kinase A activity. The selective voltage-dependent modulation of L-type calcium channels is likely to play an important role in neuronal physiology and plasticity.
Asunto(s)
Canales de Calcio/clasificación , Canales de Calcio/fisiología , Activación del Canal Iónico/fisiología , Potenciales de la Membrana/fisiología , Animales , Química Encefálica , Calcio/metabolismo , Canales de Calcio/genética , Proteínas Quinasas Dependientes de AMP Cíclico/antagonistas & inhibidores , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Neuronas/química , Oocitos , Conformación Proteica , Ratas , Proteínas Recombinantes/metabolismo , XenopusRESUMEN
Functional expression of the rat brain alpha 1A Ca channel was obtained by nuclear injection of an expression plasmid into Xenopus oocytes. The alpha 1A Ca current activated quickly, inactivated slowly, and showed a voltage dependence typical of high voltage-activated Ca channels. The alpha 1A current was partially blocked (approximately 23%) by omega-agatoxin IVA (200 nM) and substantially blocked by omega-conotoxin MVIIC (5 microM blocked approximately 70%). Bay K 8644 (10 microM) or omega-conotoxin GVIA (1 microM) had no significant effect on the alpha 1A current. Coexpression with rat brain Ca channel beta subunits increased the alpha 1A whole-cell current and shifted the current-voltage relation to more negative values. While the beta 1b and beta 3 subunits caused a significant acceleration of the alpha 1A inactivation kinetics, the beta 2a subunit dramatically slowed the inactivation of the alpha 1A current to that seen typically for P-type Ca currents. In situ localization with antisense deoxyoligonucleotide and RNA probes showed that alpha 1A was widely distributed throughout the rat central nervous system, with moderate to high levels in the olfactory bulb, in the cerebral cortex, and in the CA fields and dentate gyrus of the hippocampus. In the cerebellum, prominent alpha 1A expression was detected in Purkinje cells with some labeling also in granule cells. Overall, the results show that alpha 1A channels are widely expressed and share some properties with both Q- and P-type channels.
Asunto(s)
Encéfalo/fisiología , Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio/fisiología , Neuronas/fisiología , Oocitos/fisiología , omega-Conotoxinas , Ácido 3-piridinacarboxílico, 1,4-dihidro-2,6-dimetil-5-nitro-4-(2-(trifluorometil)fenil)-, Éster Metílico/farmacología , Animales , Encéfalo/metabolismo , Canales de Calcio/biosíntesis , Canales de Calcio/efectos de los fármacos , Núcleo Celular/fisiología , ADN Complementario/metabolismo , Femenino , Expresión Génica , Hibridación in Situ , Sustancias Macromoleculares , Proteínas de la Membrana/efectos de los fármacos , Proteínas de la Membrana/fisiología , Venenos de Moluscos/farmacología , Neuronas/metabolismo , Oocitos/efectos de los fármacos , Especificidad de Órganos , Péptidos/farmacología , Plásmidos , Sondas ARN , Ratas , Venenos de Araña/farmacología , Xenopus laevis , omega-Agatoxina IVA , omega-Conotoxina GVIARESUMEN
The rat brain class C calcium channel alpha 1 subunit cDNA, rbC-II, was subcloned into a vertebrate expression vector and transient expression was assayed following nuclear injection into Xenopus oocytes. Whole cell recordings showed that rbC-II currents (recorded with 40 mM Ba2+ as the charge carrier) had variable activation rates and minimal inactivation over an approximately 700 msec depolarizing step pulse. The pharmacological properties of the rbC-II current were consistent with those of an L-type calcium channel, being sensitive to dihydropyridines (10 microM nifedipine blocked approximately 85% of the current, 10 microM Bay K 8644 enhanced the current between 2- and 10-fold) and not affected by the N- and P-type calcium channel antagonists, omega-conotoxin GVIA and omega-agatoxin IVA, respectively. Coexpression of rbC-II with cloned rat neuronal calcium channel alpha 2 and beta subunits resulted in several changes to the electrophysiological properties of the rbC-II current including, an increased whole cell peak current, an increased rate of activation and a hyperpolarizing shift in the voltage dependence of activation. Taken together with results showing that the neuronal class D alpha 1 subunit also encodes an L-type calcium channel [Williams M. E., Feldman D. H., McCue A. F., Brenner R., Velicelebi G., Ellis S. B. and Harpold M. M. (1992a) Neuron 8: 71-84], these results indicate that the mammalian nervous system expresses two distinct genes encoding L-type calcium channels.
Asunto(s)
Canales de Calcio/metabolismo , Neuronas/metabolismo , Animales , Química Encefálica , Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio/efectos de los fármacos , Canales de Calcio/genética , Femenino , Neuronas/efectos de los fármacos , Oocitos/metabolismo , Plásmidos , Ratas , Xenopus laevisRESUMEN
A number of pharmacologically and electrophysiologically distinct voltage-dependent Ca2+ channels have been identified in mammalian neurons. Two rat brain Ca2+ channel alpha 1 subunits (rbC-I and rbC-II) have been isolated by molecular cloning and shown to be highly related (95%) to the cardiac dihydropyridine-sensitive Ca2+ channel. The rbC-II protein is distinct from rbC-I in that it contains a 3 amino acid insert in the putative cytoplasmic loop between domains II and III and a 28 amino acid substitution corresponding to the third transmembrane segment (S3) of the fourth domain. We show that rbC-I and rbC-II transcripts are generated by alternative splicing and that they are differentially expressed in the rat CNS.
Asunto(s)
Encéfalo/metabolismo , Canales de Calcio/genética , ADN Recombinante , Empalme del ARN , Secuencia de Aminoácidos , Animales , Canales de Calcio/metabolismo , Genes , Datos de Secuencia Molecular , Oocitos/metabolismo , Ratas , Transcripción Genética , XenopusRESUMEN
Intravenous infusion of L-NG-nitro-arginine, an inhibitor of endothelial nitric oxide (NO) synthesis, produced vasoconstriction in the coronary, cerebral, renal and duodenal vascular beds of the conscious rabbit. In this study, using radiolabelled microspheres, we provide in vivo evidence for a basal NO-dependent vasodilator tone in the coronary vascular bed.
Asunto(s)
Arginina/análogos & derivados , Vasos Coronarios/efectos de los fármacos , Vasoconstricción/efectos de los fármacos , Animales , Arginina/farmacología , Vasos Coronarios/fisiología , Infusiones Intravenosas , Masculino , Óxido Nítrico/fisiología , Nitroarginina , Conejos , Resistencia Vascular/efectos de los fármacosRESUMEN
A recent paper by Clark and Iqbal [Opt. Lett. 15, 1291 (1990)] proposed a novel modification of the conventional Fabry-Perot technique for measuring losses in semiconductor optical waveguides, which they claim eliminates the need for any knowledge of the reflectivities of the waveguide end facets. We show that the range of validity of this technique is quite limited and in many situations may be difficult to verify.
RESUMEN
From an analysis of the effects of end facet reflections on measurements of the characteristics of optical waveguide directional couplers, we show that these reflections can result in uncertainties of almost 6 dB in measurements of coupler extinction ratios. We present methods for estimating and minimizing these uncertainties. We also show that the Fabry-Perot loss measurement technique, which is widely used for measurements of single waveguides, can be used for loss measurements on directional couplers, but only for high extinction ratio devices.
RESUMEN
We examined the effect of substance P, a potent stimulator of endothelium-derived relaxing factor (EDRF) release, on responses to collagen and adenosine 3',5'-diphosphate (ADP) in an in vivo model of platelet aggregation. Substance P inhibited platelet aggregation induced in vivo by both collagen and ADP. This anti-platelet effect was particularly pronounced against collagen-induced aggregation and was prevented by prior administration of haemoglobin (Hb), a known inhibitor of EDRF-mediated responses. Collagen-induced platelet aggregation in vitro was unaffected by a concentration of substance P equivalent to that achieved in plasma following in vivo administration. This study provides a clear demonstration of the anti-platelet activity of EDRF in vivo and an indication that its effectiveness may depend on the aggregating agent used.