L-733,060, a novel tachykinin NK1 receptor antagonist; effects in [Ca2+]i mobilisation, cardiovascular and dural extravasation assays

Short RNA species that encompass the psi domain of the retroviral genome spontaneously form dimers in vitro, and the retroviral nucleocapsid protein activates this dimerization in vitro. Addition of gag RNA sequences downstream of the 3' end of the psi domain decreases the level of spontaneous dimerization. Here, we report the effects of RNA length on dimerization in vitro, studied with RNA fragments from Moloney murine leukaemia virus that contain the psi domain and all or part of the gag sequence. Extension of the RNA leads to progressive inhibition of the in vitro dimerization process. Sequences located downstream of the 3' end of the psi domain seem to stabilize the monomeric structures. This stabilization participates in dimerization of the RNA sequences involved in the recognition of two RNA molecules. We studied the ability of nucleocapsid protein 10 to promote dimerization of such long RNA fragments, and found that the protein greatly enhances their dimerization in vitro. We propose that nucleocapsid protein 10 stimulates the overall dimerization process by reduction of the energy barrier that must be overcome to allow dimer formation. Our results show that dimerization of RNA form Moloney murine leukaemia virus in vitro is enhanced by nucleocapsid protein 10. This finding is in agreement with the involvement of the nucleocapsid protein in RNA dimerization in vivo.     

Antinociceptive activity of the tachykinin NK1 receptor antagonist, CP-99,994, in conscious gerbils

1. The ability of CP-99,994, and its less active enantiomer, CP-100,263, to inhibit spontaneous behaviours and hyperalgesia induced by central infusion of the NK1 receptor agonist, GR73632 or intraplantar injection of formalin was investigated in rats and gerbils. 2. GR73632 (3 pmol, i.c.v.)-induced foot tapping in gerbils was dose-dependently inhibited by CP-99,994 (0.1-1 mg kg-1, s.c.), but not by CP-100,263 (10 mg kg-1, s.c.) using pretreatment times up to 60 min. The centrally active dose-range for CP-99,994 was increased to 1-10 mg kg-1 s.c. with a higher challenge dose of GR73632 (30 pmol, i.c.v.). 3. In gerbils, intrathecal (i.t.) injection of GR73632 (30 pmol) elicited behaviours (licking, foot tapping or flinching and face washing) which closely resembled, but which was less specifically localized than, behaviours seen in animals injected with formalin (0.1-5%) into one hindpaw. 4. In rats, CP-100,263, but not CP-99,994 (up to 30 mg kg-1), inhibited the early phase response to intraplantar injection of 5% formalin (ID50 = 13.9 mg kg-1). The late phase was inhibited by both compounds (ID50 values 36.3 and 20.9 mg kg-1, respectively). In gerbils, there was marginal evidence for enantioselective inhibition of the early phase induced by formalin (2%). The ID50 values were 6.2 mg kg-1 for CP-99,994 and 13.4 mg kg-1 for CP-100,263. 5. Intrathecal injection of GR73632 (30 pmol) caused thermal hyperalgesia in igerbils which was inhibited enantioselectively by s.c. administration of CP-99,994 (ID50= 2.46 mg kg-1), but not by CP-100,263 (30 mg kg-1).6. In gerbils, intraplantar injection of formalin (0.1%) caused thermal hyperalgesia which was inhibited by CP-99,994 (ID50= 1.1 mg kg-1, s.c.). There was a nonsignificant trend for an anti-algesic effect of CP-100,236 (estimated ID50 = 8.2 mg kg-1, s.c.).7 These findings support the proposal that NK1 receptor antagonists may be useful in the clinical management of pain and reinforce the need to dissociate specific and nonspecific antinociceptive effects of available compounds.     

In vivo pharmacology of an angiotensin AT1 receptor antagonist with balanced affinity for AT2 receptors

L-163,017 (6-[benzoylamino]-7-methyl-2-propyl-3-[[2'-(N-(3-methyl-1-butoxy) carbonylaminosulfonyl)[1,1']-biphenyl-4-yl]methyl]-3H-imidazo[4,5- b]pyridine) is a potent, orally active, nonpeptide angiotensin II receptor antagonist. Conscious rats and dogs were dosed p.o. and i.v.; in both species the plasma bioequivalents are similar at the angiotensin AT1 and AT2 receptor sites indicating balanced activity is maintained in vivo. L-163,017 prevents the pressor response to intravenous (i.v.) angiotensin II in the conscious rat, dog, and rhesus monkey. L-163,017 also significantly reduces blood pressure in a renin-dependent model of hypertension, similar to an angiotensin converting enzyme inhibitor (Enalapril) and an angiotensin AT1 receptor-selective antagonist (L-159,282). These studies indicate that neither the angiotensin AT2 receptor nor bradykinin is important in the acute antihypertensive activity of angiotensin converting enzyme inhibitors or angiotensin II receptor antagonists.     

In vitro pharmacological properties of KRH-594, a novel angiotensin II type 1 receptor antagonist

Although most people are thought to receive their highest acute exposures to gasoline while refueling, relatively little is actually known about personal, nonoccupational exposures to gasoline during refueling activities. This study was designed to measure exposures associated with the use of an oxygenated fuel under cold conditions in Fairbanks, Alaska. We compared concentrations of gasoline components in the blood and in the personal breathing zone (PBZ) of people who pumped regular unleaded gasoline (referred to as regular gasoline) with concentrations in the blood of those who pumped an oxygenated fuel that was 10% ethanol (E-10). A subset of participants in a wintertime engine performance study provided blood samples before and after pumping gasoline (30 using regular gasoline and 30 using E-10). The biological and environmental samples were analyzed for selected aromatic volatile organic compounds (VOCs) found in gasoline (benzene, ethylbenzene, toluene, m-/p-xylene, and o-xylene); the biological samples were also analyzed for three chemicals not found in gasoline (1,4-dichlorobenzene, chloroform, and styrene). People in our study had significantly higher levels of gasoline components in their blood after pumping gasoline than they had before pumping gasoline. The changes in VOC levels in blood were similar whether the individuals pumped regular gasoline or the E-10 blend. The analysis of PBZ samples indicated that there were also measurable levels of gasoline components in the air during refueling. The VOC levels in PBZ air were similar for the two groups. In this study, we demonstrate that people are briefly exposed to low (ppm and sub-ppm) levels of known carcinogens and other potentially toxic compounds while pumping gasoline, regardless of the type of gasoline used.     

Effects of a tachykinin NK3 receptor antagonist, SR 142801, studied in isolated neonatal rat spinal cord

In the ovariectomized (ovx) rat, the nonsteroidal antiestrogens, clomiphene (CLO) and tamoxifen (TAM), at dose levels that prevent development of osteopenia to a degree approaching that of 17beta-estradiol are, in contrast to 17beta-estradiol, only weakly uterotrophic. Metabolites of CLO and TAM might contribute differentially to these effects. Thus, we have evaluated bone protective and uterine effects in ovx rats of two such metabolites: 4-hydroxy CLO, produced by p-hydroxylation of CLO; and 4HTA, produced from TAM by stepwise replacement of its dimethylaminoethyl side chain with an acetic acid moiety, accompanied by p-hydroxylation. Also reported are effects of D4HTA, the dihydrodesethyl derivative of 4HTA previously characterized as a full estrogen mimetic in vitro. Administration of 4-hydroxy CLO (2.5 mg/kg subcutaneously) 5 days/week for 5 weeks to 3-month-old ovx rats resulted in complete prevention of bone loss and suppression of bone turnover to levels comparable to those of intact controls and to those of ovx animals similarly receiving 17beta-estradiol (10 microg/kg). However, uterine weight in animals receiving 4-hydroxy CLO was 64% less than that in 17beta-estradiol-treated animals. Although 4HTA (3.7 mg/kg s.c.) had a modest uterotrophic effect, it did not prevent bone loss associated with ovariectomy. In contrast, D4HTA (3.6 mg/kg s.c.) partially reduced bone turnover indicators and cancellous bone loss in a manner similar in many ways to that observed in TAM-treated ovx animals, but it had no uterotrophic effect. These results suggest that, although 4HTA does not contribute to the bone-protective effect of TAM, 4-hydroxy CLO might augment that of CLO.     

Gly166 in the NK1 receptor regulates tachykinin selectivity and receptor conformation

We have studied the pharmacological properties of genetically engineered human NK1 tachykinin receptors in which residues at the extracellular surface of the fourth transmembranal domain were substituted with the corresponding amino acids from the NK2 receptor. We show that substitution of G166C:Y167F in the human NK1 receptor induces high affinity binding of a group of tachykinin ligands, known as 'septides' (i.e. neurokinin A, neurokinin B, [pGlu6,Pro9]-substance P6-11 and substance P-methylester). In contrast, binding of substance P and non-peptide antagonists is unaffected by these mutations. This effect parallels that found on the rat receptor and is therefore species specific. Second, we demonstrate that mutation of Gly166 to Cys alone is both necessary and sufficient to create this pan-reactive tachykinin receptor, whereas replacement of Tyr167 by Phe has no detectable effect on the pharmacological properties of the receptor. Furthermore, analysis of the effect of N-ethylmaleimide and dithiothreitol on binding of radiolabelled substance P documents differences in the mode in which this ligand interacts with wild-type and mutant receptors and supports the existence of a mutational induced change in the conformational status of the NK1 receptor.     

Effect of a non-peptide NK-2 tachykinin receptor antagonist on LH, FSH, and prolactin release by rat hemipituitaries in vitro

Tachykinins are present in the anterior pituitary gland and there is evidence that they may have a direct intrapituitary role influencing the secretion of some of the hormones released by this gland. In this investigation, we have studied the effect of the non-peptide NK-2 receptor antagonist SR 48,968 (Sanofi Recherche) on the basal release of LH, FSH, and prolactin by rat hemipituitaries incubated in vitro, and also on the response to GnRH. SR 48,968 significantly inhibited prolactin release into the medium. The highest doses of this compound stimulated the basal release of LH by hemipituitaries from castrated, castrated testosterone-treated, and ovariectomized estradiol-treated rats, but not from intact male rats. SR 48,968 significantly inhibited the release of LH in response to GnRH. Since some tachykinin receptor antagonists have been demonstrated to act also on calcium channels, studies with verapamil, a calcium channel antagonist, were also carried out for comparison. Verapamil inhibited prolactin release into the medium and decreased the LH response to GnRH. These results suggest that tachykinins that bind NK-2 receptors, may have an intrapituitary role stimulating the release of prolactin, and that they may also modulate the response of the gonadotrophs to GnRH. The fact that verapamil shares some of the actions exerted by NK-2 receptor antagonists on the pituitary glandm however, suggests the possibility that some of the effects of NK-2 receptor antagonists may be mediated through calcium channel antagonism. Therefore, the results observed with the use of some of these antagonists should be interpreted with great caution.     

The tachykinin NK1 receptor antagonist, RP67580, inhibits the bradykinin-induced rise in intracellular Ca2+ concentration in bovine pulmonary artery endothelial cells

The bradykinin-induced rise in intracellular Ca2+ concentration ([Ca2+]i) and the bradykinin receptor involved in this response were characterized in bovine pulmonary artery endothelial cells. It was found that bradykinin induces an intracellular biphasic Ca2+ response, consisting of a transient peak followed by an elevated plateau phase. Both bradykinin and the bradykinin B1 receptor agonist, des-Arg9-bradykinin, induced a concentration-dependent increase in [Ca2+]i, but the bradykinin-induced rise was much greater. Moreover, the bradykinin-induced [Ca2+]i rise could be inhibited by the bradykinin B2 receptor antagonists, D-Arg0[Hyp3, Thi(5,8), D-Phe7]bradykinin and Hoe 140 (D-Arg[Hyp3, Thi5, D-Tic7, Oic8]bradykinin), but not by the bradykinin B1 receptor antagonist, des-Arg9-[Leu8]bradykinin. From these results it can be concluded that a bradykinin B2 receptor is involved in this response. Furthermore, we found that the tachykinin NK1 receptor antagonist, RP67580 ([imino 1 (methoxy-2-phenyl)-2 ethyl]-2 diphenyl 7,7 perhydroisoindolone-4 (3aR, 7aR)), and its negative enantiomer, RP68651 (2-[1-imino 2-(2 methoxy phenyl) ethyl] 7,7 diphenyl 4-perhydroisoindolone (3aS-7aS)), could inhibit the bradykinin-induced [Ca2+]i response, although no functional tachykinin NK1 receptors were found. Binding studies evidenced no binding of RP67580 or RP68651 to the bradykinin receptor. We conclude that RP67580 inhibits the bradykinin-induced rise in [Ca2+]i via a bradykinin B2 receptor-independent mechanism.     

In vitro characterization of tachykinin NK2-receptors modulating motor responses of human colonic muscle strips

BACKGROUND: Endothelium plays a key role in graft patency. My colleagues and I have developed a verapamil+nitroglycerin solution (balanced to pH 7.4) to prepare the radial artery without mechanical distention or dilation and have reported the efficacy of its antispastic action. This study was designed to investigate whether using this solution as part of the University of Hong Kong protocol to prepare the radial artery is more efficacious than papaverine solution in preserving endothelial function. METHODS: Ring segments of the radial artery taken from 25 patients undergoing coronary artery bypass grafting were studied in organ chambers. The endothelium-dependent relaxation, as the index of endothelial function, was examined by two mechanisms-receptor-mediated relaxation (by acetylcholine) and non-receptor-mediated relaxation (by calcium ionophore A23187) in U46619-induced contraction (10 nmol/L). RESULTS: In the relaxation induced by either acetylcholine (27.3% +/- 5.0% [n = 7] vs 23.9% +/- 3.9% [n = 6],p = 0.6) or A23187 (62.9% +/- 6.0% [n = 13] vs 62.3% +/- 8.4% [n = 6],p = 0.96), there was no significant difference between the control radial arteries and those treated with the verapamil+nitroglycerin solution. In the papaverine-treated rings, acetylcholine-mediated relaxation was abolished (3.3% +/- 2.6% vs 23.9% +/- 3.9%,p < 0.001) and A23187-mediated relaxation was significantly reduced (39.7% +/- 5.2% vs 62.3% +/- 8.4%, p = 0.02) compared with verapamil+nitroglycerin treatment. CONCLUSION: Use of verapamil+nitroglycerin solution to prepare the radial artery maximally preserves endothelial function. In contrast, papaverine impairs this function. Verapamil+nitroglycerin solution may be effectively and safely used to prepare the radial artery for coronary artery bypass grafting.     

In vivo characterisation of ZM 241385, a selective adenosine A2A receptor antagonist

The in vivo characterisation of ZM 241385 (4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-+ ++ylamino] ethyl)phenol), a novel, non-xanthine, selective adenosine A2A antagonist is described. In anaesthetised dogs ZM 241385 (i.v.) was 140-fold more potent in attenuating vasodilator responses to exogenous adenosine in the constant flow perfused hind limb than the bradycardic effects. In pithed rats in which blood pressure was supported by angiotensin II infusion, ZM 241385 (10 mg kg-1, i.v.) did not inhibit the hypotensive or bradycardic effects of the A3/A1 receptor agonist N(6)-2-(4-amino-3-iodophenyl)ethyladenosine (APNEA). In conscious spontaneously hypertensive rats, ZM 241385 (3-10 mg kg-1, p.o.) selectively attenuated the mean arterial blood pressure response produced by exogenous adenosine. No inhibition of the bradycardic effects of adenosine was observed following these doses of ZM 241385. The results indicate that ZM 241385 can be used to evaluate the role of adenosine A2A receptors in the action of adenosine in vivo.     

Impaired IL-1beta-induced neutrophil accumulation in tachykinin NK1 receptor knockout mice

Tachykinin NK1 receptors play an important role in the development of neurogenic inflammatory responses. We have used the murine air-pouch model to investigate whether the neurogenic component of the cellular inflammatory response to interleukin-1beta (IL-1beta, 10 ng into the air-pouch) is altered in NK1 receptor knockout mice compared to wild type controls. Air-pouches were washed following a 4 h IL-1beta treatment, the wash collected and neutrophil number estimated using a Neubauer haemocytometer. The response to IL-1beta was significantly attenuated in NK1 receptor +/- (40% reduction) and -/- mice (62% reduction) compared to wild type controls (+/+), whilst the response to cytokine-induced neutrophil chemoattractant (CINC, 0.3 microg) was unaffected. The response to substance P (7.5 nmol) was attenuated by approximately 50% in both NK1 receptor +/- and -/- mice compared to wild type controls. In conclusion NK1 receptors play a significant role in the cellular response to IL-1beta in a model of inflammation.     

A tachykinin NK3 receptor antagonist, SR 142801 (osanetant), prevents substance P-induced bronchial hyperreactivity in guinea-pigs

Aerosolized substance P (0.1 M, for 30 min) induced airway hyperresponsiveness in guinea-pigs 24 h after they were pre-treated with salbutamol (8.7 mM by aerosol for 10 min) and phosphoramidon (0.1 mM by aerosol for 10 min). This was displayed by an exaggerated response to the bronchoconstrictor effect of acetylcholine. A microvascular leakage hypersensitivity also occurred and was demonstrated by a potentiation of the plasma protein extravasation from bronchial vessels induced by histamine. The aim of this study was to investigate the effects of the non-peptide and potent tachykinin NK3 receptor antagonist, SR 142801 (osanetant), in comparison with those of the tachykinin NK1 and NK2 receptor antagonists, SR 140333 (nolpitantium) and SR 48968 (saredutant) respectively, on substance P. When given once at 1 mg/kg i.p. 45 min before exposure to substance P, SR 142801 prevented both hyperresponsiveness to acetylcholine and the potentiation of histamine-induced increase in microvascular permeability. SR 142801 did not exhibit any tachykinin NK1 or NK2 antagonistic activity in experiments on guinea-pig isolated airways, in vitro or in vivo. The results suggest that tachykinin NK3 receptors might be involved in these substance P-induced effects on airways.     

In vitro properties of a high affinity selective antagonist of the VIP1 receptor

A selective high affinity VIP1 receptor antagonist [Acetyl-His1, D-Phe2, Lys15, Arg16, Leu17] VIP(3-7)/GRF(8-27) or PG 97-269 was synthesized, by analogy with recently obtained selective VIP1 receptor agonists. The properties of the new peptide were evaluated on Chinese hamster ovary (CHO) cell membranes expressing either the rat VIP1-, rat VIP2- or the human VIP2-recombinant receptors and on LoVo cell membranes expressing exclusively the human VIP1 receptor. The IC50 values of 125I-VIP binding inhibition by PG 97-269 were 10, 2000, 2 and 3000 nM on the rat VIP1-, rat VIP2-, human VIP1- and human VIP2 receptors, respectively. PG 97-269 had a negligible affinity for the PACAP I receptor type. It did not stimulate adenylate cyclase activity, but inhibited competitively effect of VIP on the VIP1 receptor mediated stimulation of adenylate cyclase activity. The Ki values were respectively of 15 +/- 5 nM and 2 +/- 1 nM for the rat and human VIP1 receptors. Thus the described molecule in the first reported VIP antagonist with an affinity in the nM range and with a high selectivity for the VIP1 receptor subclass. It may be useful for evaluation of the physiological role of VIP in rat and human tissues.     

Pharmacological profiles of a novel non-peptide angiotensin II type I receptor antagonist HR720 in vitro and in vivo

The relationship, in 539 individuals infected with the human immunodeficiency virus (HIV), between two prognostic markers, the CD4 count and beta-2-microglobulin (B2M), and the development of the acquired immunodeficiency syndrome (AIDS) and death was investigated. Cox proportional hazards models were used to determine the risk of AIDS or death. In a multivariate model which adjusted for demographic factors and treatment, the most recent measurements of B2M (relative hazard (RH) 1.37 per g/l higher) and CD4 count (RH 2.17 per log-unit lower) were both significantly associated with the development of AIDS. Similarly, in a multivariate model which additionally adjusted for the development of AIDS as a time dependent covariate, there was a strong relationship with risk of death for the most recent measurements of B2M (RH 1.34 per g/l higher), and CD4 lymphocyte count (RH 1.91 per log-unit lower). A difference in the level of B2M could be used among patients with similar CD4 counts as an indicator of increased risk of progression to AIDS or death. Using the most recent values of these markers provides a better estimate of the risk of AIDS or death, compared to the more common method of analysis, where baseline values of the markers are used.     

2-Nitrophenylcarbamoyl-(S)-prolyl-(S)-3-(2-naphthyl)alanyl-N-benzyl-N - methylamide (SDZ NKT 343), a potent human NK1 tachykinin receptor antagonist with good oral analgesic activity in chronic pain models

A lead compound which had sub-micromolar affinity for the rabbit NK1 receptor but negligible affinity for rat NK1 receptors, 3a, was discovered by directed screening. 2-Substitution in the ring of the benzylthiourea substituent in the initial lead was found to be important, and halogens (Cl, Br) in this position were found to improve affinity for the human receptor. The activity of a series of 2-halo-substituted benzylthioureas was then optimized by modification of the proline diphenylmethyl amide, guided by a simple conceptual model based on structural overlay between these early antagonists and NK1 selective peptides. In this way, aromatic amino acid amides were identified which had improved affinity with respect to the starting diphenylmethyl (DPM) amides. The first sub-nanomolar ligand for the human NK1 receptor which arose from this series, 4af, combined a 2-chlorobenzylthiourea unit with a 2-naphthylalanine amide. Contemporaneously it was discovered that the benzylthiourea unit could be simplified to a phenylthiourea providing that an appropriate 2-substituent was also incorporated. Combination of these two series gave 2-NO2 phenylthiourea analogues which led directly to the analogous urea, 5f (2-nitrophenylcarbamoyl-(S)-prolyl-(S)-3-(2-naphthyl)alanyl-N-benz yl- N-methylamide, SDZ NKT 343), a highly potent ligand for the human NK1 receptor (Ki = 0.16 nM). In addition to its high in vitro potency, 5f proved to be a potent orally active analgesic in guinea pig models of chronic inflammatory and neuropathic pain. The nature of the 2-aryl substituent was found to be critical for oral activity in this series. Clinical evaluation of 5f as a novel analgesic agent is currently underway.     

In vitro and in vivo antibacterial activities of Q-35, a novel fluoroquinolone

Q-35, a new fluoroquinolone, was evaluated for its in vitro and in vivo antibacterial activities. In vitro antibacterial activity against gram-positive bacteria was almost equal to that of sparfloxacin or tosufloxacin, but its activity against gram-negative bacteria was 2 times or more lower than that of other quinolones tested. In experimental septicemia, the in vivo activity of Q-35 reflected its in vitro antibacterial activity. In respiratory tract infections with Streptococcus pneumoniae TMS-3 in mice, Q-35 showed a therapeutic effect similar to sparfloxacin and tosufloxacin. Q-35 showed almost the same activity as that of ofloxacin in mice with pyelonephritic infection due to Escherichia coli TMS-3. The peak levels of Q-35 in murine serum, lungs and kidneys after a single oral administration were intermediate compared to those of tested quinolones.     

In vitro and in vivo antibacterial activities of OPC-20011, a novel parenteral broad-spectrum 2-oxaisocephem antibiotic

OPC-20011, a new parenteral 2-oxaisocephem antibiotic, has an oxygen atom at the 2- position of the cephalosporin frame. OPC-20011 had the best antibacterial activities against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), Enterococcus faecalis, and penicillin-resistant Streptococcus pneumoniae: MICs at which 90% of the isolates were inhibited were 6.25, 6.25, and 0.05 microg/ml, respectively. Its activity is due to a high affinity of the penicillin-binding protein 2' in MRSA, an affinity which was approximately 1,050 times as high as that for flomoxef. Against gram-negative bacteria, OPC-20011 also showed antibacterial activities similar to those of ceftazidime. The in vivo activities of OPC-20011 were comparable to or greater than those of reference compounds in murine models of systemic infection caused by gram-positive and -negative pathogens. OPC-20011 was up to 10 times as effective as vancomycin against MRSA infections in mice. This better in vivo efficacy is probably due to the bactericidal activity of OPC-20011, while vancomycin showed bacteriostatic activity against MRSA. OPC-20011 produced a significant decrease of viable counts in lung tissue at a dose of 2.5 mg/kg of body weight, an efficacy similar to that of ampicillin at a dose of 10 to 20 mg/kg on an experimental murine model of respiratory tract infection caused by non-ampicillin-susceptible S. pneumoniae T-0005. The better therapeutic efficacy of OPC-20011 was considered to be due to its potent antibacterial activity and low affinity for serum proteins of experimental animals (29% in mice and 6.4% in rats).     

The tachykinin NK1 receptor. Part I: ligands and mechanisms of cellular activation

The tachykinin NK1 receptor is widely expressed in the mammalian central and peripheral nervous system. Powerful pharmacological tools (agonists and antagonists) are now available to elucidate the physiological role of NK1 receptors at these levels, as well as to understand their role in diseases and establish the possible therapeutic usefulness of NK1 receptor antagonists for treatment of human diseases. The structure-activity studies that have led to the development of potent peptide and non-peptide ligands for the tachykinin NK1 receptor are here reviewed. Among the peptide agonists and antagonists, linear and cyclic sequences have been developed. The non peptide antagonists belong to different chemical classes, i.e. steroids, perhydroisoindolones, quinuclidines, piperidines and tryptophane derivatives. The first non peptide antagonists for NK1 receptors have been obtained by random screening of chemical compounds large collections. The resulting leads were optimized with 'classic' structure activity approaches, aiming at identifying 'common' motifs for interaction with the receptor by ligands of different chemical classes. The results derived from the recent application of molecular biology techniques were useful to drive the design of new ligands toward a precise structural definition of ligand-receptor bi-molecular interactions. Studies on mutant receptors have established that the sites of interaction of peptide agonists and non peptide antagonists with the tachykinin NK1 receptor are largely non overlapping. Moreover, data obtained from mutagenesis of the NK1 receptor further indicate that some amino acid residues in the NK1 receptor sequence are critical for determining the binding affinity of some but not all ligands. Therefore, different antagonists discovered from random screening may not possess common points of interaction or common structural and conformational characteristics for their interaction with the tachykinin NK1 receptor. The tachykinin NK1 receptor couples with G-proteins to determine its biological effects in target cells. Several G-proteins both sensitive (Go, Gi) and insensitive (Gq, G11) to pertussis toxin can mediate the action of NK1 receptors. Moreover, several second messanger signalling systems (elevation of intracellular calcium, stimulation of phosphoinositol turnover, arachidonic acid mobilization, cAMP accumulation) have to be activated following NK1 receptor signalling. Also a direct modulation of certain ion channels at membrane level has been proposed. The NK1 receptor undergoes prompt and significant tachyphylaxis upon exposure to the agonist: this has been shown to be linked with receptor internalization which also occurs physiologically when the NK1 receptor is stimulated by endogenous tachykinins.