Acetylcholine Antagonists Research Articles

Cholinergic manipulation alters stimulus‐evoked metabolic activity in cat somatosensory cortex

The role of acetylcholine (ACh) in cerebral cortical activity has recently been reevaluated. It now seems clear that this neurotransmitter increases the magnitude of cortical responses. Although substantial information has been gathered regarding the role of ACh in sensory information processing, little is known about the participation of ACh in the organization of maps in the cerebral cortex. To address this issue, we used 2 methods to manipulate the supply of ACh in the somatosensory cortex of cats: 1) unilateral neurotoxic lesions of the basal forebrain and 2) unilateral topical applications of the cholinergic antagonist, atropine. For each experimental condition, the animal received an injection of 2-deoxyglucose (2DG) while identical somatic stimuli were delivered to the right and left forepaws. In the somatosensory cortex, the 2DG uptake most often occurred in the form of patches that extended from layer II to IV. When the patches were reconstructed into 2-dimensional maps of activity throughout the somatosensory cortex, they formed strips that ran in the rostrocaudal direction. The reconstructed maps revealed that the 2DG patterns in ACh-depleted and the normal cortex were similar in their overall topographic distribution. Depletion or antagonism of ACh, however, caused the stimulus-evoked metabolic label to be reduced in dimension and density. Measurements of background activity levels were obtained by using 1) cytochrome oxidase histochemistry or 2) metabolic activity values in regions of somatosensory cortex that were not specifically stimulated. This analysis indicated that background values in the ACh-depleted hemispheres were not different from those in the normal hemispheres. The absence of ACh therefore appears to reduce the cortical response to stimulation, while background activity values do not change. These observations indicate that ACh plays a significant role in the processing of sensory information and the organization of somatosensory cortical maps.

Scopolamine produces locomotor stereotypy in an open field but apomorphine does not

Both dopaminergic and nondopaminergic drugs produce hyperlocomotion in rats. Dopaminergic drugs also produce focused stereotypy (absence of locomotion and intense sniffing or licking/biting of a restricted area of the environment). Some drugs produce repetitive routes of locomotion; this phenomenon might represent a combination of hyperlocomotion and stereotypy. Scopolamine (an acetylcholine antagonist) and apomorphine (a dopamine agonist) both produce hyperlocomotion in rats; apomorphine also produces focused stereotypy but scopolamine does not. This research determines whether these drugs also produce locomotor stereotypy as measured by γ. Scopolamine (0.5 and 2.0 mg/kg) produced locomotor stereotypy at both doses. Apomorphine (1.0, 2.0, and 3.0 mg/kg) failed to reliably produce locomotor stereotypy. Thus, there is not necessarily a relationship between the ability of a drug to produce focused stereotypy and the ability of the drug to produce locomotor stereotypy.

Interaction of central serotonin and dopamine in the regulation of carbaryl-iduced tremor

Carbaryl (50–200 mg/kg, p.o.) produced dose-dependent tremors and inhibition of striatal AChE activity. A dose-dependent elevation of striatal 5-HT and 5-HIAA levels was also observed with carbaryl but at the higher doses (100–200 mg/kg p.o.). L-Trp or 5-HTP or haloperidol potentiated the carbaryl-induced tremors. Further, 5-HTP or haloperidol, when administered (i) alone, reduced the ED 50 value and increased the duration of carbaryl-induced tremors without affecting the maximum tremorogenic response of rats and (ii) together, did not change any of these measures significantly. Atropine (acetylcholine antagonist) completely blocked the tremors produced by carbaryl in the absence or presence of 5-HTP or haloperidol. Methysergide (5-HT antagonist) and bromocriptine (DA agonist) antagonised the potentiating effect of 5-HTP and haloperidol, respectively, on the carbaryl-induced tremors. Furthermore, bromocriptine antagonised the potentiating effect of 5-HTP on the carbaryl-induced tremor but, methysergide failed to achieve this antagonism in presence of haloperidol. These results indicate that carbaryl-induced tremors primarily involve the activation of central cholinoceptors and that the serotonergic potentiation of carbaryl-induced tremors is possibly mediated through the dopaminergic disinhibition of cholinergic neurons.

ChemInform Abstract: Solid‐State Stereochemistry of Anhydrous (‐)‐Scopolamine Hydrobromide

The solid-state structure of anhydrous (Nr,Cα-S)-(–)-scopolamine hydrobromide [(–)-hyoscine], an acetylcholine antagonist, has been determined by single crystal X-ray diffraction analysis. (–)-Scopolamine hydrobromide [anhydrous form] gives crystals belonging to the orthorhombic P212121 space group, and at 298 K: a= 7.348(1), b= 10.482(1), c= 22.867(1)A, V= 1 761.26(1)A3, Z= 4, R(F)= 0.053, and RW(F)= 0.049. The (S)-absolute configuration was determined from the effects of anomalous dispersion of the bromide atom. The N-methyl group exists in an axial, configuration similar to that previously described for the hemihydrate. However, in the anhydrous form the tropate residue exhibits a different conformation from that noted for the hemihydrate. The tropate ester moiety in (Nr,Cα-S)-(–)-scopolamine hydrobromide [anhydrous form] and (Ns,Cα-S)N-butylhyoscinium bromide both exhibit very similar crystalline-state conformations, while that in the hemihydrate form is reasonably similar to (Ns,Cα-S)-(–)-hyoscyamine hydrobromide [(–)-atropine].

Inhibitory effects of amitriptyline on the stimulation-induced Ca 2+ increase in parotid acini

The present study demonstrates the effects of the antidepressant, amitriptyline, and the acetylcholine antagonist, atropine, on the stimulation-induced rise in cytosolic, free Ca 2+ (Ca 2+). The changes in Ca i 2+ of collagenase-isolated rat parotid acini were measured by means of the Ca 2+ -sensitive dye, fura-2. It was found that stimulation by carbachol resulted in a maximal increase of 582 ± 34 nM (mean ± S.E.) in Ca i 2+ with a k S of 5.8 ± 1.3 μM. Adrenaline caused a rise of 380 ± 22 nM in Ca i 2+ with a k S of 0.5 ± 0.2 μM. Amitriptyline and atropine were found to inhibit the carbachol-induced rise in Ca i 2+ with dissociation constants (k I of 105 and 1.25 nM, respectively, in the absence of agonist. The adrenergic-induced rise in Ca i 2+ was inhibited by amitriptyline with a k I of 45 nM. Amitriptyline was found to inhibit both receptor classes by a competitive or mixed type of inhibition. Similarly, atropine exerted the same type of inhibition on the acetylcholine receptor. Amitriptyline and atropine were found to be mutually exclusive for competing for substrate binding on the receptor. These findings are consistent with a common binding site for amitriptyline and atropine on the acetylcholine receptor, possibly in close proximity with, but different from the substrate binding site. The stimulation-induced cell shrinkage evoked by the loss of electrolytes and water from the acini was measured by a 90° light scattering signal. It was found that this method makes possible the detection of autonomic side-effects of antideprassants on acini suspended in protein-containing media.

Acetylcholine modifies neuronal acoustic rate‐level functions in guinea pig auditory cortex by an muscarinic receptors

Cholinergic modification of neuronal responsiveness in auditory cortex includes alteration of spontaneous and tone-evoked neuronal discharge. Previously it was suggested that the effects of acetylcholine (ACh) and muscarinic agonists on neuronal discharge resembled those due to increases in the intensity of acoustic stimuli (Ashe et al. 1989). To determine the relationship between neuronal modifications due to ACh acting at muscarinic receptors and those due to changes in stimulus intensity, we determined acoustic rate-level functions for neurons in the auditory cortex of barbiturate-anesthetized guinea pigs before, during and after administration of ACh. ACh facilitated acoustic rate-level functions in 82% of the cells tested. In addition, during ACh administration 66% of neurons responded to stimuli that were previously subthreshold, that is, ACh decreased the response threshold. Cholinergic facilitation of rate-level functions was attenuated by the general muscarinic antagonist atropine. The nature of the muscarinic receptors involved in the actions of ACh was further examined by presenting single tones before, during, and after administration of ACh and specific muscarinic receptor subtype antagonists, either pirenzepine (M1) or gallamine (M2). ACh-induced facilitation of spontaneous and tone evoked neuronal discharge was antagonized by pirenzepine, but not by gallamine, suggesting the involvement of the M1 muscarinic receptor subtype. These data indicate that ACh can facilitate stimulus-evoked responses and decrease response thresholds for neurons in auditory cortex, possibly via activation of M1 muscarinic receptors. Such effects of ACh acting at muscarinic receptors could underly cholinergic regulation of information processing in the auditory cortex.

The effect of leukotriene antagonists, lipoxygenase inhibitors and selected standards on leukotriene-mediated allergic bronchospasm in guinea pigs.

Leukotrienes (LT) C4, D4, and E4 are major contributors to the pathobiology of human bronchial asthma. Therefore, it is likely that compounds that antagonize the action or inhibit the formation of LTs will be useful therapeutic agents. We have studied the effects of LT antagonists, 5-lipoxygenase inhibitors and selected standards in a model of LT-mediated allergic bronchospasm in guinea pigs. Sensitized animals were pretreated with mepyramine, indomethacin and propranolol to eliminate the influence of histamine, prostaglandins, thromboxanes and circulating catecholamines. In these animals, inhalation of antigen resulted in a bronchospasm consistent with a LT-mediated response that was slow in onset, of long duration and was inhibited by the selective LTD4, antagonists FPL-55712, LY-171,883 and ICI-198,615. ICI-198,615 was approximately 50-times more potent than FPL-55712 by the intravenous and intratracheal routes. However, of thirteen compounds known to inhibit 5-lipoxygenase and LT biosynthesis in vitro only phenidone, piriprost and AA-861 were active in this in vivo model. The allergic bronchospasm was inhibited by bronchodilators (e.g. PGE2, aminophylline and forskolin) and by some mast cell stabilizers, but was otherwise insensitive to other pharmacological classes of compounds including calcium channel blockers and antagonists of serotonin, acetylcholine and platelet-activating factor. This model seems useful and reasonably selective for the evaluation of new antianaphylactic compounds that are LT antagonists. The inactivity of many 5-lipoxygenase inhibitors in this model suggests they do not inhibit LT formation in vivo.

Interactions between hypoxia, acetylcholine and dopamine in the carotid body of rabbit and cat.

1. Acetylcholine (ACh) and dopamine (DA) were either infused into the carotid artery or applied directly to the surface of the carotid body of twenty-six rabbits and fifteen cats. Afferent discharge of single chemoreceptor units was recorded at a range of Pa,O2 (arterial O2 pressure) values during drug administration. 2. There were no observable systemic effects of either drug when applied to the surface of the carotid body. 3. Acetylcholine tended to depress afferent discharge when applied to the surface of the rabbit carotid body or when infused into the carotid sinus. In the cat, intracarotid and surface application of ACh had mild and inconsistent effects. DA consistently depressed discharge in both species independent of the route of administration. Antagonists of ACh and DA failed to abolish the chemoreceptor response to hypoxia. 4. The changes in afferent discharge elicited by all drugs were small compared with the range of discharge rates attained with physiological stimuli. The effects of ACh and DA were more marked in hyperoxia than in hypoxia for both routes of administration, disappearing at Pa,O2 values close to 20 Torr (7.5 Torr = 1 kPa). 5. A role for DA in the maintenance of the hypoxic response was investigated in six rabbits. After 15 min of hypoxia (Pa,O2 = 21.8 +/- 1.1 Torr; mean +/- S.E.M.) the discharge of single chemoreceptor fibres adapted moderately (to 79.3 +/- 5.2% of maximum discharge). Following administration of domperidone or haloperidol (1.0-5.3 mg kg-1, I.V.) the same fibres responded with equal magnitude to the onset of the hypoxic stimulus but showed a significantly larger adaptation (to 48.5 +/- 4.4%). 6. It is concluded that endogenous ACh and DA are unlikely to mediate the transduction process of the carotid body, but DA may play a role in preventing adaptation to a prolonged hypoxic stimulus.

The effect of strontium on the drug-receptor interaction on cholinergic drugs

The effect of replacing calcium with strontium in the perfusion fluid was qualitatively and quantitatively studied in the isolated longitudinal muscle of the guinea-pig ileum. In the presence of strontium hyoscine could be considered a competitive antagonist of acetylcholine for the acetylcholine receptor of the longitudinal muscle of the guinea-pig ileum; dibenamine still blocked this receptor in an irreversible way. The equilibrium constants for acetylcholine (K A) and hyoscine (K I) were obtained in the presence of calcium (K A = 3.16 ± 0.63 μM; K I = 0.38 ± 0.07 nM), and strontium (K A = 7.00 ± 0.89 μM; K I = 0.93 ± 0.16 nM). The results show a decrease in the affinity of both drugs for the muscarinic receptor in the presence of strontium.

Solid-state stereochemistry of anhydrous (–)-scopolamine hydrobromide

The solid-state structure of anhydrous (Nr,Cα-S)-(–)-scopolamine hydrobromide [(–)-hyoscine], an acetylcholine antagonist, has been determined by single crystal X-ray diffraction analysis. (–)-Scopolamine hydrobromide [anhydrous form] gives crystals belonging to the orthorhombic P212121 space group, and at 298 K: a= 7.348(1), b= 10.482(1), c= 22.867(1)Å, V= 1 761.26(1)Å3, Z= 4, R(F)= 0.053, and RW(F)= 0.049. The (S)-absolute configuration was determined from the effects of anomalous dispersion of the bromide atom. The N-methyl group exists in an axial, configuration similar to that previously described for the hemihydrate. However, in the anhydrous form the tropate residue exhibits a different conformation from that noted for the hemihydrate. The tropate ester moiety in (Nr,Cα-S)-(–)-scopolamine hydrobromide [anhydrous form] and (Ns,Cα-S)N-butylhyoscinium bromide both exhibit very similar crystalline-state conformations, while that in the hemihydrate form is reasonably similar to (Ns,Cα-S)-(–)-hyoscyamine hydrobromide [(–)-atropine].

Neurotensin and prostaglandin interactions in smooth muscle of the guinea pig stomach

Neurotensin, xenopsin and neuromedin N had a biphasic effect (initial small relaxation followed by a sustained contraction) on the motility of longitudinal muscle strips from the guinea pig gastric corpus. Kinetensin was without effect. Tetrodotoxin, adrenaline, histamine, 5-hydroxytryptamine, opioid peptides, angiotensin II and antagonists of acetylcholine, and desensitization of the strips to bradykinin did not modify the action of neurotensin. The contraction phase was inhibited in a concentration-dependent manner by indomethacin and acetylsalicylate, demonstrating that this activity of neurotensin was dependent on prostaglandin synthesis. The preparation responded to exogenous prostaglandins E 1, E 2, F 1α and F 2α with concentration-dependent contractions. The relaxation phase was abolished by verapamil and apamin, indicating the presence of inhibitory neurotensin receptors on smooth muscle cells that are linked to ionic channels.

Effects of anti-asthma drugs on PAF-induced death in mice

A number of anti-asthma drugs was assayed for the ability to protect mice from platelet-activating factor (PAF)-induced death, which has been suggested to be dependent on the bronchoconstrictive features of this autacoid. Salbutamol, dexamethasone, theophylline, ketotifen and zindotrine, administered parenterrally, produced a dose-dependent protection, while forskolin, enprofylline, disodium cromoglycate, nedocromil, azelastine and antagonists of acetylcholine, histamine and serotonin were devoid of protective effects. Theophylline, contrary to salbutamol, lost its protective effects in adrenalectomized mice, suggesting that these effects are dependent on the release of adrenomedullary cathecolamines. Salbutamol, theophylline and dexamethasone, at doses capable of inhibiting PAF-induced death, did not affect PAF-induced haemoconcentration in mice, thus excluding widespread changes in vascular permeability as a major cause of death. These results are generally in agreement with the hypothesis that airway obstruction is an important determinant of PAF-induced death in mice.

Role of cholinergic and GABAergic neuronal systems in cycloheximide-induced amnesia in mice

The role of cholinergic and GABAergic neuronal systems on the cycloheximide (CXM)-induced amnesia was investigated using the step-down-type passive avoidance task in mice. CXM (7.5–120 mg/kg, SC) given just after the training caused amnesia (indicated by short latency to step down from the platform on the grid floor) in the retention test conducted 24 hr later in a dose-dependent fashion. In the CXM (60 mg/kg)-treated mice, a choline esterase inhibitor, physostigmine (PHY; 0.125 and 0.25 mg/kg, IP), or GABA agonists, muscimol (1 and 2 mg/kg, IP) and baclofen (6 and 12 mg/kg, IP), given just after training markedly prolonged step down latency (SDL), indicating reversal of amnesia. The antiamnesic action of PHY (0.125 mg/kg) was almost completely antagonized by a central acetylcholine antagonist, scopolamine (3 mg/kg, SC), but not by a peripheral acetylcholine antagonist, butylscopolamine (3 mg/kg, SC). Furthermore, the antiamnesic action of muscimol (2 mg/kg) was reversed by GABA antagonists, picrotoxin (0.5 mg/kg, SC) and bicuculline (0.5 mg/kg, SC), while the effect of baclofen (12 mg/kg) was reversed by picrotoxin (0.5 mg/kg), but not by bicuculline (0.5 mg/kg). These results suggest that the dysfunction of cholinergic and GABAergic neuronal systems play an important role in the CXM-induced memory impairment on the passive avoidance task.

Catecholamine effects upon rat hypothalamic corticotropin-releasing hormone secretion in vitro.

To further our understanding of the functional role of catecholaminergic systems in regulating hypothalamic corticotropin-releasing hormone (CRH) secretion, we assessed the direct effects of a multiplicity of catecholamine agonists and antagonists on hypothalamic CRH secretion. To accomplish this, we used an in vitro rat hypothalamic organ culture system in which CRH secretion from single explants was evaluated by a specific RIA (IR-rCRH). Norepinephrine (NE) stimulated IR-rCRH secretion dose dependently, with peak effects in the nanomolar range. The effect of NE was antagonized by the mixed alpha antagonist phentolamine, the alpha 1 antagonist prazosin, and the alpha 2 antagonist yohimbine, but not by the beta blocker, L-propanolol. Compatible with these data were the findings that the alpha 1 agonist phenylephrine and the alpha 2 agonist clonidine both stimulated IR-rCRH secretion in a dose-dependent fashion. On the other hand, whereas the beta agonist, isoproterenol, caused a weak, non-dose-dependent increase in IR-rCRH secretion, this effect could not be antagonized by L-propanolol. Despite pretreatment with serotonin and acetylcholine antagonists, the effect of NE upon IR-rCRH secretion was undiminished, suggesting that NE-induced CRH secretion is not mediated by either neurotransmitter. On the other hand, pretreatment with gamma-aminobutyric acid (GABA) attenuated NE-induced IR-rCRH secretion. Whereas epinephrine (E) stimulated IR-rCRH secretion, this occurred only at higher concentrations, and was antagonized by phentolamine, but not by L-propanolol. Dopamine (DA) had a weak stimulatory effect that could be antagonized by the DA1 receptor antagonist, SCH 23390, but not by phentolamine. We conclude that NE and E stimulate hypothalamic IR-rCRH secretion via alpha 1 and alpha 2 receptors. The effect of NE upon IR-rCRH secretion is not apparently mediated by serotonergic or cholinergic interneurons, but is modulated by the inhibitory neurotransmitter, GABA. These data support the idea that the central catecholaminergic systems are excitatory rather than inhibitory upon CRH secretion when acting directly at the hypothalamic level.

Combined cold urticaria and cholinergic urticaria--clinical characterization and laboratory findings.

Thirteen patients with both cold and cholinergic urticaria are reported. There was considerable variability, particularly in the cold urticaria which was of the common cold contact type in seven patients, of the generalized cold induced cholinergic type in two and in four patients the lesions induced by direct contact with ice were morphologically like cholinergic urticaria, but appeared despite prior application of an acetyl choline antagonist. The natural history, laboratory findings and the effects of therapy are discussed.

Background activity pattern of guinea pig septal neurons in vitro

Activity of medial septum-diagonal band cells (MS-DB neurons) was investigated in slices of guinea pig septum. Four types of activity were distinguished on the basis of interspike interval distribution and coefficient of variation (CV): extremely regular (CV 0.3 0.7), and rhythmic bursting patterns. Activity of cells belonging to the first group was resistant to superfusion with a medium low in Ca2+ and high in Mg2+ which produces blockade of synaptic effects. The same applied to a percentage of neurons with a rhythmic bursting pattern. Activity pattern of Mg2+-resistant bursting cells also remained unchanged by the effects of GABA and acetylcholine antagonists. It is concluded that cells with properties of regular and bursting endogenous pacemakers are found in the MS-DB.

Platelet activating factor (PAF) is a potent stimulator of porcine tracheal fluid secretion in vitro

Mocus hypersecretion is a major clinical feature of chronic obstructive lung diseases such as asthma. The possible role of the inflammatory and bronchoconstrictor ether lipid PAF (platelet activating factor) has been studied in isolated porcine trachea with the tantalum ‘hillock’ technique used to visualize fluid production from tracheal submucosal glands. PAF caused a rapid, dose-dependent (0.001-1 nM) stimulation of fluid secretion which could be detected after 5 min and which increased with time up to at least 15 min. The PAF-induced fluid secretion was unaffected by both antagonists of histamine, acetylcholine and leukotriene D 4 and inhibitors of prostaglandin and leukotrienes synthesis. A purported PAF receptor antagonist (CV 3988) inhibited the PAF responses in a dose-dependent manner implying a receptor-mediated event. These results may be of relevance to the mucus hypersecretion seen in chronic airway diseases.

Effects of calcium antagonists on muscarinic receptor subtypes in the rat brain

The effects of several calcium antagonists, including nicardipine, nifedipine, verapamil, and diltiazem, on muscarinic acetylcholine antagonist binding were studied in the P 2 fraction of the rat cerebral cortex using either [ 3H]quinuclidinyl benzilate ([ 3H]QNB) or [ 3H]pirenzipine as the radioactive ligand. (1) The potency of [ 3H]QNB binding inhibition was in the ordernicardipine>verapamil>diltiazem>nifedipine. The IC 50 values of nicardipine, verapamil, and diltiazem were 2.56 × 10 −6 M, 1.28 × 10 −5 M, and 6.00 × 10 −5 M, respectively. (2) The inhibition of [ 3H]QNB binding by nicardipine was significantly decreased in the presence of Ca ions. (3) In saturation experiments of [ 3H]QNB binding in the presence of nicardipine, the K d value appeared to be significantly affected, but the B max value was unchanged. This indicated that nicardipine probably inhibited [ 3H]QNB binding allosterically. On the other hand, (4) nicardipine inhibited [ 3H]pirenzipine binding completely with an IC 50 value of 7.87 × 10 −7 M. It was concluded that nicardipine had an inhibitory effect on M 1-receptor binding.

Effects of acetylcholine agonists and antagonists on yawning and analgesia in the rat

The ability of acetylcholine muscarinic agonists, injected subcutaneously (s.c.) to elicit yawning and analgesia (tail-flick response) in rats was examined. Yawning was elicited by physostigmine, RS86 and pilocarpine with an inverted ‘U’-shaped dose-response relationship; maximal effects occurred at 0.1, 0.5 and 2.0 mg/kg respectively. Neostigmine (0.05–0.2 mg/kg); arecoline (0.5–2.0 mg/kg); bethanecol (0.1–10 mg/kg) and McN-A-343 (5–20 mg/kg) had marginal or no activity. In contrast, dose-related analgesia was obtained following oxotremorine (0.01–0.3 mg/kg) and arecoline (0.5–4.0 mg/kg) and physostigmine (0.1–0.4 mg/kg), RS86 (0.25–2.5 mg/kg) and pilocarpine (0.5–8.0 mg/kg). The effects of acetylcholine antagonists on physostigmine-induced yawning and physostigmine-induced analgesia were also investigated. Following their s.c. injection, trihexyphenidyl, atropine, dicyclomine, secoverine and methylatropine but not pirenzepine, inhibited both yawning and analgesia; there were clear differences in their potencies on the two responses. Pirenzepine, intracerebroventricularly (i.c.v.), inhibited yawning (ED 50 value 5.7 μg/rat) but not analgesia (3–100 μg/rat). The results are discussed in terms of a possible functional differentiation of central muscarinic receptors.

Plasma protein extravasation induced by mammalian tachykinins in rat skin: influence of anaesthetic agents and an acetylcholine antagonist.

The effect of mammalian tachykinins on plasma protein extravasation was assessed in the rat dorsal skin. Substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) increased vascular permeability in a dose-related manner with a threshold dose of about 0.07 pmol in sodium pentobarbitone-anaesthetized animals. Plasma protein extravasation induced by the tachykinins was 100-500 times less in magnitude in animals anaesthetized with urethane. Plasma protein extravasation induced by SP (66 pmol) was significantly reduced (63%; P less than 0.001) by atropine (a muscarinic inhibitor) while that induced by NKA or NKB was unaffected by the inhibitor suggesting that a cholinergic component might only be involved in the vascular permeability elicited by SP. The rank order of potency for the tachykinins on plasma protein extravasation was: NKB greater than SP greater than NKA (in absence of atropine) and NKB greater than NKA greater than SP (in presence of atropine), suggesting that this vascular response is mediated by a SP-E receptor type. The amplitudes of the plasma protein extravasation induced by NKB and its hydrophilic analogue [Arg degrees]NKB were similar, indicating that the lipophilic features of the native peptide cannot account for its potent biological activity. Plasma protein extravasation was enhanced by the SP analogue [D-Pro4,Lys6,D-Trp7,9,10,Phe11]SP (4-11), thus showing the limitation of such SP analogues (antagonists) for characterizing the tachykinin receptors involved in vascular permeability.