Mechanisms of histamine release by compound 48/80

1. Rat and guinea-pig lung tissues were incubated for 20 min at 37 degrees C in Krebs-Ringer phosphate buffer at pH 7.4, or in Tyrode-Tris buffer at pH 8.2, and the release of histamine produced by adding different concentrations of compound 48/80 to the incubation medium was determined.2. At pH 7.4, increasing concentrations of 48/80 increased the release of histamine from the rat lung, with a tendency towards a maximum. No release of histamine from guinea-pig lung was observed at this pH. At pH 8.2, histamine release occurred both from rat and guinea-pig lung, and was proportional to the logarithm of the concentration of compound 48/80.3. Histamine release from rat lung by 20 mug/ml. of 48/80 decreased when the pH was raised from 7.4 to 8.2; but the release caused by 1 mg/ml. of 48/80 increased both in rat and guinea-pig lung as the pH was raised.4. 2-4-Dinitrophenol (DNP) inhibited the release of histamine from rat lung by a concentration of 20 mug/ml. of 48/80; the inhibition was prevented by glucose. DNP did not affect histamine release from rat or guinea-pig lung by a concentration of 1 mg/ml. of 48/80 and enhanced the release when the pH was raised from 7.4 to 8.2.5. 1 mg/ml. of 48/80 did not inhibit the enhanced oxygen consumption produced by DNP in the isolated rat diaphragm.6. Iodoacetic acid (IAA) or a Ca/Mg-free medium inhibited the release of histamine by 20 mug/ml. of 48/80 from rat lung but not the release produced by 1 mg/ml. in either rat or guinea-pig lung.7. The degranulation of rat mesentery mast cells caused by 20 mug/ml. of compound 48/80 was inhibited by DNP. The degranulation evoked by 1 mg/ml. of 48/80 was also sensitive to this inhibitor; in this instance, however, the metachromatic staining reaction of the mesentery mast cells was greatly diminished.8. It is concluded that two processes of histamine release by compound 48/80 occur in rat lung. One, dependent on cell metabolism, involves, mast cell granule secretion. The other, independent of cell metabolism, seems to consist of a simple exchange reaction between histamine and compound 48/80, and this is the only one occurring in guinea-pig lung.     

Inhibition of histamine release from human lung and rat peritoneal mast cells by cyclosporin-A.

Cyclosporin A (CS-A) partly inhibited IgE-mediated histamine release from human lung tissue in vitro (chopped and collagenase-dispersed preparations). Inhibition started at concentrations within the clinical blood level of the drug, but the IC50 was much higher (10-50 microM; 50% inhibition reached only in some experiments). CS-A also inhibited histamine release from rat peritoneal mast cells (RPMC) induced by antigen, concanavalin-A (Con-A), compound 48/80 and ionophore A23187. The IC50 values were 0.3, 23.0, and 33.0 microM for Con-A, A23187 and ovalbumin respectively. Inhibition of 48/80-induced release did not reach 50%. By comparison with human basophils the human lung and RPMC were less sensitive to the inhibitory action of CS-A. The IgE-mediated Schultz-Dale reaction in human lung strips was slightly and inconsistently inhibited by CS-A, but IgG1-mediated reaction in guinea-pig lung strips was potentiated by the drug.     

Inhibition of histamine release from dispersed human lung and tonsillar mast cells by nicardipine and nifedipine

Calcium entry blocking drugs attenuate antigen-induced bronchoconstriction in asthma which is mast cell mediated. We have investigated the effects of two calcium uptake blockers, nicardipine and nifedipine on histamine secretion from human mast cells dispersed from lung and tonsillar tissue. Mast cells were activated for secretion with anti-human IgE or calcium ionophore, A23187. Nicardipine and nifedipine caused a concentration-related inhibition of IgE-dependent histamine release from both lung (IC30 10 microM and 4.4 microM) and tonsillar (IC30 21 microM and 47 microM) mast cells. Nicardipine and nifedipine also inhibited mast cell histamine release induced by A23187 with IC30 values of 14 microM and 67 microM for lung and 15 microM and 30 microM for tonsillar mast cells. In the absence of drugs, increasing the extracellular calcium concentrations from 0.2 to 5 mM caused a concentration related increase in IgE-dependent histamine release from tonsillar mast cells. Both nicardipine and nifedipine (50 microM) displaced the concentration-effect curve to the right. Nicardipine (0.01-100 microM) caused a concentration related inhibition of rat kidney histamine methyltransferase activity used in the radioenzymatic assay of histamine (ki of 7.5-12 microM) whereas nifedipine was only a weak inhibitor. Nicardipine also interfered with the spectrofluorimetric assay after exposure to ultraviolet light. These observations demonstrate that nicardipine and nifedipine inhibit IgE-dependent and ionophore stimulated mediator secretion from human mast cells. The lack of stimulus-related specificity and the high drug concentrations required suggest that classical calcium channel blockade is not responsible for inhibition of mast cell mediator release. Furthermore, we suggest that inhibition of mast cell mediator release is unlikely to be the mechanism by which these drugs alleviate asthma.     

Histamine release from mast cells of various species induced by histamine releasing factor from human lymphocytes

The aim of our work was to investigate the effect of histamine releasing factor (HRF), produced in vitro by lymphocytes obtained from atopic and non-atopic asthmatics, on mast cells of various species (mouse - peritoneal mast cells, hamster and rat - peritoneal and pleural mast cells, guinea-pig - mesenteric and pulmonary mast cells). We found that human HRF is able to release histamine from the examined mast cell populations in a dose-dependent fashion. Mast cells from various species differed in their susceptibility to the action of HRF; rat pleural and guinea-pig mesenteric and pulmonary mast cells were the most susceptible, while mouse and hamster peritoneal mast cells - the least susceptible. The presence of 50% D2O in the medium significantly increased HRF-induced histamine release from rat mast cells, while the addition of phosphatidylserine did not change it. HRF-induced histamine release from guinea-pig mesenteric mast cells was not related to sensitization of these cells. We also compared histamine release from guinea-pig pulmonary and mesenteric mast cells induced by human HRF produced in vitro by lymphocytes obtained from atopic and non-atopic asthmatics. We have found that supernatant from atopic asthmatics lymphocyte cultures released significantly more histamine than supernatant from non-atopic asthmatics lymphocyte cultures. Our studies give evidence that human HRF acts across the species barrier and induces histamine release from mast cells of various species. The mechanism of HRF action on mast cells seems to be different from that of allergen.     

Some studies of the action of betahistine at H1 and H2 receptors for histamine

Betahistine produced a concentration-dependent contraction of the guinea-pig ileum and was about 27 times less active than histamine in this respect. Betahistine induced desensitization of contractile responses to histamine in the guinea-pig ileum. The H1 histamine receptor antagonist mepyramine was a competitive antagonist of the action of betahistine on the guinea-pig ileum. Betahistine caused relaxation of the rat uterus contracted by acetylcholine, and this action of betahistine was blocked by the H2 receptor antagonist cimetidine. Betahistine had a concentration-dependent positive chronotropic action on isolated guinea-pig atria, and in this respect was tenfold less potent than histamine. The action of betahistine on the atria was blocked by the H2 receptor antagonist YM11170. Betahistine caused a concentration-related contraction of the isolated lung parenchymal strip of the guinea-pig, and YM11170 potentiated this effect. Betahistine failed to release histamine from rat peritoneal mast cells at concentrations up to 100 microM and it did not prevent histamine release induced by either substance P or anti-IgE. Betahistine produced a dose-related flare and wheal reaction when injected intradermally into human skin. It is concluded that betahistine has agonist activity at both H1 and H2 receptors for histamine.     

Physiological concentrations of zinc inhibit the release of histamine from human basophils and lung mast cells

We have previously shown that physiological concentrations of zinc (congruent to 7 X 10(-6) M) inhibit the release of histamine from human basophil leukocytes (Marone et al., J. Pharmacol. Exp. Ther. 217: 292, 1981). In these experiments we compared the effect of zinc chloride on the release of chemical mediators from human basophils and mast cells isolated from human lung. Preincubation (5 min, 37 degrees C) of human basophils and lung mast cells with zinc chloride (10(-6)-3 X 10(-5) M) caused dose-related inhibition of histamine and peptide leukotriene C4 (LTC4) release induced by anti-IgE. Increase Ca2+ concentrations (0.3 to 6 mM) in the extracellular medium completely reversed the inhibitory effect of zinc on anti-IgE-mediated histamine secretion. Zinc chloride was a competitive antagonist of the action of Ca2+ in histamine secretion induced by anti-IgE with a dissociation constant (Kd) of about 10(-5) M in both the basophil and mast cell systems. Thus physiological concentrations of zinc inhibit the release of histamine from human basophils and lung mast cells, presumably by blocking Ca2+ uptake induced by anti-IgE activation.     

Some studies on the release of histamine from mast cells treated with d-tubocurarine

d-Tubocurarine (dTc) released histamine in non-cytotoxic fashion from peritoneal mast cells of the rat, mouse and hamster. The response was similar to that evoked by other cationic liberators such as compound 48/80 and polylysine in that it was extremely rapid and enhanced by calcium-deprivation at suboptimal concentrations of secretagogue. Tissue mast cells obtained by enzymic dissociation of the heart, lung and mesentery of the rat and guinea pig were unreactive or hyporesponsive to the effect of dTc. The compound liberated only very small amounts of histamine from isolated preparations of perfused guinea pig heart but significantly increased the rate and contractility of the heart. These results are discussed in terms of the general functional heterogeneity of mast cells from different locations.     

Differential release of histamine and 5-hydroxytryptamine from rat mast cells: the contribution of amine uptake to the apparent pattern of secretion.

Despite the fact that mast cells isolated from rat mesentery and lung tissue contain 5-HT in excess of histamine, the pattern of amine output, in response to compound 48/80, mirrors that in peritoneal mast cells where histamine is in excess of 5-HT, such that this secretagogue induces a greater percentage release of histamine than 5-HT. Mast cells are capable of taking up both these amines, although uptake of 5-HT is in preference to that of histamine. With concentrations of clomipramine and fluoxetine that inhibited 5-HT uptake, the net percentage release of 5-HT increased in a corresponding manner, and the concentration-effect curves in response to compound 48/80 ran in a collinear fashion with that of control histamine output (measured in the absence of the drugs). Both drugs had no effect upon the uptake or secretion of histamine. Thus, observed differences in the apparent pattern of histamine and 5-HT secretion from rat mast cells may be due to selective reuptake of amines rather than a reflection of differential amine release.     

Induction of histamine release from human skin mast cells by bradykinin analogs

Kinins are potent proinflammatory peptides that induce histamine release from rodent mast cells. We examined the ability of bradykinin, lysylbradykinin and a series of kinin analogs to cause histamine release from human basophils, human lung mast cells and human skin mast cells. At concentrations ranging from 0.1 microM to 1 mM, bradykinin failed to cause histamine release from any of the human histamine-containing cells studied. Lysylbradykinin was also without effect on basophils and lung mast cells, but was a weak secretagogue for human skin mast cells, inducing 5.5 +/- 3% (mean +/- SD) of total cellular histamine release at a concentration of 10(-5) M. Similarly, when sixteen recently developed bradykinin antagonists were examined, these compounds had no effect on basophils or lung mast cells but all sixteen induced dose-dependent histamine release from skin mast cells. The release process was temperature dependent and, at a concentration of 10(-5) M, the antagonists induced 8-27% histamine release. Although preincubation of cells with 10(-3) M bradykinin or des(Arg9) bradykinin significantly inhibited antagonist-induced histamine release, the requirement for such high concentrations of these peptides to cause inhibition suggested that histamine release is not mediated by either B1 or B2 kinin receptors. To understand further the mechanism of histamine release, we examined a series of bradykinin analogs with single amino acid substitutions in the bradykinin sequence. Replacement of proline7 in the bradykinin sequence with D-phenylalanine is the essential change used to convert kinin analogs into antagonists, and 10(-5) M [DPhe7]-bradykinin induced 8-10% histamine release. Other analogs, devoid of antagonist activity, however, such as [DPhe6]-bradykinin and [LPhe7]-bradykinin were able to induce equivalent levels of histamine release. The ability to induce histamine release appears to be related, at least in part, to aromaticity, since [DTrp6]-bradykinin and [DTrp7]-bradykinin induced greater amounts of histamine release than equivalent [DPhe]-analogs, causing approximately 20% histamine release at 10(-5) M. By contrast, [DAla7]-bradykinin was an ineffective stimulus. In summary, a single amino acid substitution can convert bradykinin into a secretagogue for human skin mast cells. The ability of kinin analogs to induce histamine release from skin mast cells, but not lung mast cells or basophils, emphasizes the heterogeneity of human histamine-containing cells.     

Histamine secretion from mast cells treated with chlortetracycline (aureomycin): a novel calcium ionophore

The novel calcium ionophore chlortetracycline (CTC) induced histamine secretion (less than or equal to 90%) from isolated rat peritoneal mast cells in a pH and dose-dependent fashion. The process was dependent on exogenous calcium ions and was inhibited by extremes of temperature and metabolic blockers. The release was rapid, being essentially complete within 1 min, but the half-life of the process varied inversely with the concentration of the ionophore. In contrast to receptor-mediated ligands, but in keeping with other ionophores, the activated state induced by CTC did not decay with time. The secretion was effectively inhibited, according to the concentration of the ionophore, by disodium cromoglycate and other anti-allergic or cyclic AMP-active drugs. These results confirm our previous contention that these agents do not act on receptor-mediated calcium-channels. CTC induced a significant (less than or equal to 50%) release of histamine from enzymically dispersed rat mesenteric mast cells but was essentially inactive against isolated mast cells from the mesentery or lung of the guinea-pig. These results extend our former observations on the functional heterogeneity of mast cells and show that, in common with other secretagogues, ionophores may exhibit selectivity in their mode of action.     

Oxatomide inhibits the release of bronchoconstrictor arachidonic acid metabolites (iLTC4 and PGD2) from rat mast cells and guinea-pig lung

The effect of oxatomide, an orally active antiallergic drug, on immunoreactive LTC4 (iLTC4) production has been studied in rat peritoneal exudate cells (PEC) and guinea-pig lung fragments using the calcium ionophore A23187 and specific antigen in vitro. Oxatomide (10(-5) M) inhibited iLTC4 release by 70% with A23187 from rat PEC, and by 48% with antigen from guinea-pig lung. Oxatomide is supposed to affect the biosynthesis pathway of leukotrienes, because oxatomide inhibits 5-lipoxygenase from guinea-pig peritoneal leukocytes with an IC50 17 microM. Oxatomide also depressed the release of PGD2 from rat peritoneal mast cells stimulated by A23187 (IC50 4.2 microM). The effects of oxatomide on iLTC4 and PGD2 release were more potent than other antiallergic drugs (DSCG, ketotifen, tranilast).     

Synergism between thapsigargin and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate on the release of [14C]arachidonic acid and histamine from rat peritoneal mast cells

Thapsigargin is a potent skin irritating sesquiterpene lactone isolated from the roots of Thapsia garganica L. (Apiaceae). In rat peritoneal mast cells thapsigargin induced a calcium-dependent non-cytotoxic [14C]arachidonic acid and histamine release. A minor amount of the released [14C]arachidonic acid was converted to [14C]prostaglandin D2. A potentiated effect was found between thapsigargin and 12-O-tetradecanoylphorbol 13-acetate, as well as between A23187 and the phorbol ester with respect to release of [14C]arachidonic acid and histamine. It is suggested that the synergistic effect is due to activation of protein kinase C by 12-O-tetradecanoylphorbol 13-acetate and to increased intracellular calcium concentration mediated by A23187 as well as thapsigargin. [14C]arachidonic acid was released mainly from phosphatidylcholine. It is suggested that this release may be due to an action of phospholipase A2, and that protein kinase C is involved in activation of phospholipase A2.     

The effect of methyltransferase inhibitors on histamine release from human dispersed lung mast cells activated with anti-human IgE and calcium ionophore A23187

Inhibitors of adenosylmethionine (AdoMet)-dependent methyltransferases reduce histamine release from enzymatically dispersed human lung mast cells activated with either anti-human IgE or calcium ionophore A23187. The IC25 values for adenosine and 3-deazaadenosine (DZA) inhibiting anti-IgE-induced histamine release were 395 microM and 301 microM respectively. The addition of homocysteine thiolactone (Hcy) potentiated the effects of adenosine and DZA, reducing their IC25 values to 32 microM and 10.5 microM respectively. The adenosine deaminase (adenosine aminohydrolase EC 3.5.4.4) inhibitors erythro-9-(2-hydroxy-3-nonyl)-adenine (EHNA) inhibited anti-IgE-induced histamine release with an IC50 of 162 microM. This inhibition was not potentiated by Hcy. The combination of DZA and Hcy effectively inhibited histamine release induced by concentrations of A23187 which released a similar amount of histamine to anti-IgE. However the combination was 17 times less potent against A23187-compared with anti-IgE-induced release. These observations suggest that AdoMet-dependent methyltransferases play an important role in IgE-dependent histamine release from human lung mast cells but their role in A23187-induced release is less clear.     

Interaction of neurotensin with the substance P receptor mediating histamine release from rat mast cells and the flare in human skin.

1 Substance P induced histamine release from rat peritoneal mast cells in a dose-dependent manner over the concentration range 1 to 10 microM. 2 At concentrations in the range 2.5 to 1 0 microM, neurotensin produced only about 5% release of histamine, which was substantially less than the maximum effect obtained with substance P. 3 Neurotensin, 2.5 to 10 microM produced graded inhibition of histamine release induced by substance P. The inhibitory effect of neurotensin was not seen when histamine release was induced by an antigen-antibody effect of neurotensin was not seen when histamine release was induced by an antigen-antibody reaction or by the ionophore, A 23187. Some evidence was obtained to suggest that compound 48/80 may interact with the same receptor as substance P and neurotensin. 4 [D-Arg8]neurotensin, [D-Arg9]neurotensin, xenopsin and the C-terminal octapeptide of substance P (SP4-11) all inhibited histamine release by substance P, but physalaemin did not. 5 Neurotensin inhibited the wheal and flare reactions induced by substance P in human skin. 6 [D-Trp7,9]substance P released histamine from rat mast cells and was about 12 times more potent than substance P itself. [D-Trp7,9]SP1-11 also produced wheal and flare responses in human skin, being 1.8 times more potent than substance P in the production of flare.     

Antiallergic effects of astemizole on immediate type hypersensitivity reactions.

Astemizole (0.5-5 mg/kg, p.o.) dose-dependently inhibited heterologous and homologous PCA reactions in rats at ID50 values of 1.48 mg/kg and 2.37 mg/kg, respectively. The inhibitory effect of astemizole on heterologous PCA was most remarkable when this compound was given p.o. 2 h prior to antigen challenge. Astemizole (0.1-5 mg/kg, p.o.) dose-dependently inhibited experimentally-induced asthma in guinea pigs at an ID50 of 0.86 mg/kg. Ex vivo, astemizole (0.5-5 mg/kg, p.o.) inhibited antigen-induced histamine release from lung pieces of sensitized guinea pigs. In in vitro experiments, the drug dose-dependently inhibited antigen-induced histamine and SRS-A releases from guinea pig lung pieces at concentrations of 0.05-10 microM. Furthermore, astemizole (0.1-10 microM) inhibited the histamine release induced by compound 48/80 and antigen-antibody reaction from rat peritoneal mast cells, and at 0.1-500 nM inhibited both leukotriene C4- and platelet-activating factor (PAF)-induced contraction of isolated guinea pig trachea at submicromolar concentrations. Astemizole not only inhibited 45Ca uptake into rat mast cells but also prevented the Ca2+ release from the intracellular Ca store induced by compound 48/80, although this compound did not affect the histamine release from permeabilized mast cells induced by Ca2+. Our results suggest that one of the antiallergic mechanisms of astemizole may be an inhibition of signal transduction from the mast cell membrane to the intracellular systems.     

Modulation of the release of histamine and arachidonic acid metabolites from human basophils and mast cells by auranofin

In these experiments the effects of pharmacological concentrations of auranofin, a new absorbable gold compound, were assessed on the release of histamine and peptide leukotriene C4 (LTC4) from human basophils and lung mast cells. Auranofin, at pharmacological concentrations, inhibited in vitro histamine and LTC4 release from human basophils induced by anti-IgE. Inhibition began at about 3 X 10(-7) M and was maximum at 10(-5) M. We also evaluated the effect of auranofin on the release of histamine and LTC4 induced by anti-IgE from mast cells purified from human lung. Auranofin (3 X 10(-7) to 10(-5) M) dose-dependently inhibited the release of histamine and LTC4 from human lung mast cells. Thus pharmacological concentrations of auranofin cause dose-related inhibition of histamine release and de novo synthesis of LTC4 by human basophils and lung mast cells.     

Evidence of mast-cell histamine being mitogenic in intact tissue

We have reported previously that secretion by connective tissue mast cells (MCs) causes mitogenesis in adjacent cells in diverse rat tissues. In cultured rat mesentery there was a spontaneous release of about 45% of the histamine in 2 days, and a spontaneous marked increase in basal proliferation of the mesentery. The MC secretagogues, compound 48/80 and polymyxin B, released additional histamine and stimulated mitogenesis further. In contrast, 48/80 added to cultures of guinea-pig mesentery, the MC of which are unresponsive to the drug, did not affect the basal proliferation. However, exogenous histamine at 10(-10) M mitogenically stimulated the cultured guinea-pig mesentery. A histamine H2-receptor antagonist, which itself was mitogenically inert, significantly suppressed the 48/80-induced MC-mediated mitogenesis in rat mesentery in vivo and in vitro. On the other hand, a histamine H1-receptor antagonist did not affect this MC-mediated mitogenesis in rat. Our findings indicate that histamine is one of possibly several mitogens which are released or activated by the secreting MC.     

Anti-allergic constituents in the culture medium of Ganoderma lucidum. (I). Inhibitory effect of oleic acid on histamine release

The chloroform extract from Ganoderma lucidum broth markedly inhibited histamine release from rat peritoneal mast cells. From the active fractions, palmitic acid, stearic acid, oleic acid and linoleic acid were isolated. Oleic acid dose-dependently inhibited the histamine release and 45Ca uptake into mast cells induced by compound 48/80 and A-23187 at concentrations of 5 to 50 microM and 0.5 to 5 microM, respectively. Saturated fatty acids, however, had only a weak inhibitory effect on histamine release. Although linoleic acid and linolenic acid effectively prevented this release, these two compounds caused marked release at concentrations higher than 10 microM and 20 microM, respectively. Oleic acid induces membrane-stabilization in model membrane systems. It was concluded that one of the effective constituents obtainable from the chloroform extract of G. lucidum-cultured broth is oleic acid.     

Dimethyl sulfoxide decreases the fluorescence yield of the reaction between histamine and ortho-phthalaldehyde and may influence histamine release

A sensitive method for quantifying histamine is the assay based on the fluorescence of the product obtained after reacting the amine with ortho-phthalaldehyde. The presence of dimethyl sulfoxide (DMSO) even in concentrations as low as 1% decreases the yield of fluorescence. Neglecting this quenching leads to the erroneous conclusion that DMSO in a concentration dependent manner inhibits the thapsigargin induced histamine release from peritoneal rat mast cells. Apart from the release induced by the selective calcium ion mobilizers thapsigargin and ionophore A23147, DMSO potently inhibits the response to other secretagogues.     

Nanomolar concentrations of neuropeptides induce histamine release from peritoneal mast cells of a substrain of Wistar rats.

Substance P causes histamine release from rat peritoneal mast cells probably through direct activation of a specific G protein at micromolar concentrations. We found that peritoneal mast cells of a substrain of Wistar rats (Std:Wistar) responds to nanomolar concentrations of substance P by releasing histamine in a concentration-dependent manner. In addition, potent histamine release from peritoneal mast cells of the substrain rats was also induced by neurokinin A in a concentration-dependent fashion. Histamine release induced by low concentrations of substance P was significantly blocked by a tachykinin NK1 receptor antagonist, CP-96345 [(2S,3S)-cis-2-(diphenylmethyl)-N-[(2-methoxyphenyl)-methyl]-1-aza bicyclo[2.2.2]octan-3-amine dihydrochloride], whereas that induced by concentrations as high as 10 microM appeared resistant to the antagonist. The concentration-histamine release curve for neurokinin A was parallel-shifted to the right by the drug. A tachykinin NK2 receptor antagonist, SR-48968 [(S)-N-methyl-N[4-(4-acetylamino-4-phenyl piperadino)-2-(3,4-dichlorophenyl)butyl]benzamide], did not influence release stimulated by substance P and neurokinin A. On the other hand, peritoneal mast cells of Sprague-Dawley and other Wistar rats did not respond to neurokinin A. At over 1 microM but not at nanomolar concentrations, substance P caused modest histamine release from peritoneal mast cells of these rats. The results suggest that neurokinin A and nanomolar, but not micromolar concentrations of substance P stimulate tachykinin NK receptors on the peritoneal mast cells of Std:Wistar rat to release histamine.