Effect of complexes of lidocaine with transient metals on histamine release from rat mast cells.

The effect of complexes of lidocaine with zinc, copper and cobalt on histamine release from peritoneal rat mast cells induced by various secretagogues was investigated. The complexes of lidocaine with metal ions inhibited histamine release induced by compound 48/80 and ionophoreous antibiotics: A23187 and X537A. The ionic complex of lidocaine with zinc was found to be the most potent against 48/80--induced histamine release and exerted the significant inhibition in the concentration of 10(-5) M. The action of coordination complex of lidocaine with zinc was somewhat weaker. The significant inhibitory effect on 48/80-induced histamine release of the copper and cobalt lidocaine complexes was observed in concentration of 10(-4) M. Histamine release by ionophores A23187 and X537A was also affected by zinc lidocaine complexes. However, coordination complex had more potent action on histamine release than the ionic one.     

Studies on histamine-retaining granules obtained from isolated rat mast cells

Histamine-retaining granules were isolated from rat mast cells after sonication in either sucrose or Ficoll-Hypaque media. The preparations obtained were compared in regard to recovery and spontaneous loss of histamine. The effect of agents known to release histamine from intact rat mast cells (antigen, compound 48/80, decylamine, the ionophores A23187 and X537A as well as ATP) was studied on the granules. Antigen and compound 48/80 did not release histamine. Decylamine and X537A induced a pronounced release independent of the presence of divalent cations. ATP caused a small, but significant release, which showed an absolute requirement for magnesium. A23187 released histamine only in the presence of either calcium or magnesium, and this release was unaffected by certain agents known to inhibit histamine release from intact rat mast cells. The results seem to exclude the possibility that agents known to induce release of histamine from intact rat mast cells by a calcium- and energy-dependent process would exert this action through a direct effect on intracellularly localized granules.     

On the mechanism by which theophylline inhibits histamine release from rat mast cells

Theophylline (2.5 mM) did not influence the spontaneous release of histamine but inhibited histamine release induced by antigen, compound 48/80 or phosphatidylserine. The effect on 48/80-induced histamine release could not be reversed by increasing extracellular Ca2+. Exogenous adenosine (10(-8) to 10(-4) M) did not influence spontaneous histamine release or 48/80-induced release but potentiated antigen-induced release. The adenosine potentiation was competitively inhibited by theophylline in concentrations (10(-5) to 10(-4) M) lower than those required to inhibit antigen-induced histamine release in the absence of adenosine. In order to see if endogenous adenosine levels are high enough to potentiate an anaphylactic histamine release in vivo, adenosine was determined in mast cell incubates and in plasma from 4 different strains of rat. The levels were 0.18 to 0.99 microM in plasma, which is sufficient to cause significant potentiation of histamine release, but only 3 x 10(-8) M in mast cell incubates. Theophylline (2.5 mM) increased cAMP levels about 100%, whereas adenosine (10(-5) M) had little effect on cAMP and cGMP levels. However, when incubated together, adenosine could inhibit the theophylline-induced increase in cAMP levels but not the inhibition of histamine release. It is concluded that the effect of low concentrations of theophylline could be due partly to antagonism of adenosine effects. In addition, in higher doses, theophylline appears to exert an inhibitory action that is unrelated to cyclic nucleotides, extracellular calcium and adenosine.     

Evidence against a role of cyclic nucleotides in the regulation of anaphylactic histamine release in isolated rat mast cells

The effect of different phosphodiesterase (PDE) inhibitors on the antigen or 48/80 induced histamine release from isolated Hooded Lister rat mast cells was tested. The unselective PDE inhibitors theophylline (2.5 mM) and IBMX (0.2 mM) and the selective cyclic GMP PDE inhibitor M & B 22948 (0.1 mM) inhibited the antigen induced histamine release by 50% while 48/80 induced release was inhibited by about 25%. The cyclic AMP selective PDE inhibitors ICI 63197 (0.5 mM) or Ro 20-1724 (0.2 mM) had no effect on 48/80 induced histamine release but tended to enhance antigen induced release. There was no correlation between the measured levels of cyclic AMP and the effect on histamine release by the investigated PDE inhibitors. Cyclic AMP or cyclic GMP up to 10(-3) M did not affect the anaphylactic histamine release. Dibutyryl-cAMP and dibutyryl-cGMP (10(-4) M) both inhibited the release about 20% but this effect could be explained by the effect of butyric acid as sodium butyrate (2 X 10(-4) M) also inhibited the release by 20%. The presence results suggest that cyclic nucleotides are not important regulators of histamine release from isolated mast cells.     

LY 186655, a phosphodiesterase inhibitor, inhibits histamine release from human basophils, lung and skin fragments.

LY 186655 (Tibenelast, Lilly) is a new phosphodiesterase inhibitor, not derived from the xanthine, possessing bronchodilating activity in animals. The aim of this work was to study the effect of LY 186655 and theophylline on histamine release from human leukocytes, skin and lung fragments. Histamine was measured using a spectrofluorometric method. Both drugs (3 x 10(-5)-3 x 10(-3) M) exhibited a dose-dependent inhibition on anti-IgE (1/2000)-induced histamine release from human leukocytes. At 3 x 10(-3) M, theophylline was significantly more effective than LY 186655 (mean inhibition 94 and 42%, respectively). On lung fragments, theophylline and LY 186655 (3 x 10(-5)-3 x 10(-3) M) caused strong and comparable inhibitory effects on anti-IgE (1/500)-induced histamine release with a mean inhibition reaching maximally 65%. Histamine release induced by compound 48/80 (1 mg/ml) on sliced human foreskin was reduced with both drugs (3 x 10(-3) M) by about 37%. We conclude that LY 186655 inhibits in vitro immunological histamine release from human lung and cutaneous mast cells as well as basophils with a similar pattern of activity to theophylline.     

Histamine secretion from human skin slices induced by anti-IgE and artificial secretagogues and the effects of sodium cromoglycate and salbutamol

Human cutaneous mast cells show functional differences from their counterparts in other tissues. Following passive sensitization with 1% atopic serum for 30 min at 37° C human skin slices released histamine after challenge with anti-human IgE in a concentration dependent manner. Maximum release of 14 ± 2%, was achieved with a 1/10 dilution of anti-IgE. Passive sensitization with 10% atopic serum increased the secretory response to anti-IgE but histamine release was only concentration related over the entire 1/1000 to 1/10 dilution range in half of the specimens studied, the remainder showing high dose tolerance to anti-IgE, Negligible histamine release occurred with anti-IgE challenge of slices which had not been passively sensitized. The histamine releasing ability of A23187 in human skin slices was similar to that observed in lung and adenoidal mast cells being concentration dependent over the range 0-1 3 μM with a maximum release of 25 ±3%. In contrast to human lung and adenoidal mast cells, poly-L-lysine and compound 48/80 induced histamine release from skin slices. Poly-L-lysine induced a concentration-dependent release of histamine over the range 0-01-10 mUM with a maximum of 27 ± 3%. The response to compound 48/80 was variable, releasing in some but not all specimens. Histamine release caused by anti-IgE. A23187 and poly-L-lysine was shown to be dependent upon extracellular calcium while release stimulated by compound 48/80 was calcium independent. The chemotactic peptide, formyl-methionyl-leucyl-phenylalanine, over the range 0.01 10 μM failed to release histamine from skin slices. Sodium cromoglycate (100 1000 μM) failed to inhibit histamine release and the β-adrenoceptor stimulant salbutamol (1-10 μM) showed only weak activity at the lowest of three different concentrations of anti-IgE used for challenge.     

The action of tumor necrosis factor-alpha on rat mast cells.

Taking into account that cytokine tumor necrosis factor-alpha (TNF-alpha) and mast cells (MC) both are involved in inflammation, it seems of great importance to recognize their relationships. Therefore, we have studied whether recombinant human TNF-alpha (rHuTNF-alpha) can cause histamine secretion from rat peritoneal MC. We have also examined the effect of this cytokine on MC reactivity. We have established that TNF-alpha stimulates rat MC to histamine release in a concentration-dependent manner. TNF-alpha-induced histamine secretion was evoked by concentrations > 10-16 M and reached the maximum rate at a concentration of 10-10 M (histamine release 17.1% +/- 1.9%, mean +/- SEM). We have also noticed that pretreatment of MC with TNF-alpha (in a concentration of 10-16 M) significantly inhibited concanavalin A (ConA)-stimulated release of histamine, with the percent release decreasing to 51% of the control value. Treatment of mast cells with TNF-alpha resulted in a decrease of compound 48/80-dependent histamine release as well (the percent released histamine fell to 85% of the control value). This altered MC responsiveness was reversible. After 120 min of resting time, the MC reactivity came back to the initial values. We have concluded that TNF-alpha appears to be a direct stimulus for MC to release histamine, and it may regulate MC secretory function.     

Effects of norepinephrine on transmembrane calcium transport in rat mast cells

The effect of norepinephrine on transmembrane passage of calcium in rat peritoneal mast cells, was studied in an in vitro system. It was found the histamine release from mast cells induced by the ionophore A 23 187 in normal calcium medium and compound 48/80 in a calcium-free medium was suppressed by 10(-3) M norepinephrine but not at concentrations in the range 10(-5)-10(-4) M. When the secretory process is totally dependent on the presence of calcium in the incubation medium, i.e. calcium-depleted cells, 10(-5) M norepinephrine suppresses the histamine release induced by low concentrations of compound 48/80. The effect of norepinephrine (10(-5) M) on strontium-induced "spontaneous' histamine release was also studied. It was found that norepinephrine (10(-5) M) totally inhibits the progressive histamine release induced by strontium. It is possible to evoke secretion in a calcium-free medium, and subsequent introduction of Ca2+ will result in optimal histamine release. This demonstrates a secretory process in which we can distinguish between utilization of endogenous versus exogenous calcium. The release that is dependent on extracellular calcium is inhibited by norepinephrine (10(-5) M). These data indicate that the suppressive effect of norepinephrine (concentrations less than 10(-3) M) on histamine release from rat mast cells is due to an interference in transmembrane passage of calcium.     

Antiallergic Effect of Epinastine (WAL 801 CL) on Immediate Hypersensitivity Reactions: (I) Elucidation of the Mechanism for Histamine Release Inhibition

Epinastine caused an inhibition of histamine release from rat peritoneal mast cells induced by both antigen-antibody reaction and compound 48/80. Epinastine was similarly effective in inhibiting compound 48/80-induced histamine release not only from isolated rat peritoneal mast cells but also from rat mesenterial pieces. Also, histamine release from lung pieces obtained from actively sensitized guinea pigs after exposure to antigen challenge was markedly inhibited by epinastine. The drug was effective in inhibiting not only Ca²⁺ uptake into lung mast cells in actively sensitized guinea pigs but also Ca²⁺ release from the intracellular Ca store of rat peritoneal mast cells exposed to both compound 48/80 and substance P. No significant changes were observed in phosphodiesterase activity in rat peritoneal mast cells treated with epinastine, while adenylate cyclase activity was augmented by epinastine. Epinastine has no inhibitory effect on histamine release induced by Ca²⁺ or IP3 from permeabilized mast cells. However, the drug significantly and dose-dependently suppressed calmodulin activity suggesting that histamine release inhibition due to epinastine may be partly attributable to Ca²⁺-calmodulin dependent process(es). The drug caused no visible changes in thermodynamic behavior of lipids, either in order parameter or in differential scanning calorimetry, indicating that the drug has no influence on membrane fluidity.     

Effects of Angelica acutiloba on mast cell-mediated allergic reactions in vitro and in vivo

The root of Angelica acutiloba is a widely used herbal medicine which has been used as a typical therapeutic for allergic diseases in traditional medicine. This study was aimed to investigate the effects of A. acutiloba on allergic reactions in in vitro and in vivo models and its mechanism of action. A. acutiloba was extracted by maceration with 80% ethanol (AAE) and standardized by high-performance liquid chromatography. We investigated the effect of AAE on phorbol-12-myristate-13-acetate plus calcium ionophore A23187 (PMACI)-induced cytokine release; phosphorylation of JNK, ERK, and p38 in human mast cell-1 (HMC-1); and compound 48/80-induced release of histamine in rat peritoneal mast cells (RPMCs). We also investigated the effects on Evans blue (EB) extravasation induced by anti-DNP IgE in rats. Treatment with 1, 10 and 100 μg/ml AAE concentration-dependently inhibited the release of cytokines (tumor necrosis factor-α, interleukin (IL) -6, and IL-8) and phosphorylation of ERK and JNK induced by PMACI in HMC-1 cells, but it did not inhibit the phosphorylation of p38. It also inhibited compound 48/80-induced histamine release in RPMCs. Oral administration of 271?mg/kg AAE inhibited EB extravasation in a passive cutaneous anaphylaxis rat model. In conclusion, AAE inhibited mast cell-derived allergic reactions by inhibiting the release of histamine, the production of pro-inflammatory cytokines, and the phosphorylation of ERK and JNK.     

Antiallergic effect of epinastine (WAL 801 CL) on immediate hypersensitivity reactions: (I). Elucidation of the mechanism for histamine release inhibition.

Epinastine caused an inhibition of histamine release from rat peritoneal mast cells induced by both antigen-antibody reaction and compound 48/80. Epinastine was similarly effective in inhibiting compound 48/80-induced histamine release not only from isolated rat peritoneal mast cells but also from rat mesenterial pieces. Also, histamine release from lung pieces obtained from actively sensitized guinea pigs after exposure to antigen challenge was markedly inhibited by epinastine. The drug was effective in inhibiting not only Ca2+ uptake into lung mast cells in actively sensitized guinea pigs but also Ca2+ release from the intracellular Ca store of rat peritoneal mast cells exposed to both compound 48/80 and substance P. No significant changes were observed in phosphodiesterase activity in rat peritoneal mast cells treated with epinastine, while adenylate cyclase activity was augmented by epinastine. Epinastine has no inhibitory effect on histamine release induced by Ca2+ or IP3 from permeabilized mast cells. However, the drug significantly and dose-dependently suppressed calmodulin activity suggesting that histamine release inhibition due to epinastine may be partly attributable to Ca(2+)-calmodulin dependent process(es). The drug caused no visible changes in thermodynamic behavior of lipids, either in order parameter or in differential scanning calorimetry, indicating that the drug has no influence on membrane fluidity.     

Substance P-induced histamine release from human basophils, skin and lung fragments: effect of nedocromil sodium and theophylline.

We compared histamine release induced by substance P with those obtained with classical secretagogues on human basophils, lung and skin fragments. We also tested the capacity of nedocromil sodium and theophylline to inhibit histamine release in these 3 experimental models. Substance P (10(-4) M) caused a noncytotoxic histamine release (about 10% of total) from basophils, lung and skin fragments. Substance P-induced histamine release was always smaller than that obtained with optimal doses of anti-IgE, formyl-methionine phenylalanine or compound 48/80. Nedocromil sodium did not prevent secretagogue-induced histamine release from basophils or sliced skin. In contrast, it significantly inhibited anti-IgE- or substance P-induced histamine release from human lung. Theophylline caused a dose-related inhibition on these 3 models. We conclude that substance P is a modest secretagogue for human basophils and mast cells, and that skin and lung mast cells are heterogeneous with respect to their response to nedocromil sodium.     

Effect of norepinephrine on in vitro histamine release from rat mast cells.

The effect of norepinephrine on compound 48/80-induced histamine release from rat peritoneal mast cells, was studied in an in vitro system. It was found that norepinephrine, within the concentration range 10(-5)--10(-3) M, exerts a significant, dose-related, repressive effect. This effect is greatly potentiated by the beta-antagonist practolol (10(-3) M), throughout the concentration range of 10(-11)--10(-3) M norepinephrine. Methoxyamine, a selective alpha-adrenergic agonist, also represses histamine release in a dose-dependent manner; however, it is not as potent as norepinephrine. The present results would seem to suggest that the repressive effect on histamine release, observed within a low concentration range of norepinephrine, may be due to alpha-adrenoceptor mechanisms.     

Inhibitory effect of traxanox sodium on IgE-mediated histamine release from passively-sensitized mast cells of the rat in vitro

Traxanox sodium, a benzopyranopyridine derivative showing a potent oral antiallergic activity in the rat, was compared with disodium cromoglycate (DSCG) for ability to block the release of histamine from the rat mast cell in vitro. Traxanox sodium showed dose-, antigen- and time-dependent inhibiton of the IgE-mediated release of histamine. The 50% inhibitory concentration was 0.04 microM for traxanox sodium, 1 microM for DSCG and 660 microM for theophylline. All these drugs blocked the release of histamine potentiated by preincubation of the mast cell with 10 micro M adenosine at lower concentrations than those which could inhibit the IgE-mediated histamine release. In addition, traxanox sodium at concentration of 1-100 microM inhibited the histamine release caused by 0.25 microgram/ml compound 48/80 in the presence and absence of calcium, and the drug at 100 micro M slightly inhibited the release caused by 0.2 microgram/ml ionophore A23187. These results suggest that traxanox sodium is a more potent inhibitor than DSCG on the histamine release from the mast cells of the rat, and a part of its antiallergic action is due to a selective inhibition of the immunological release of allergic mediators from the mast cell.     

Potentiation of human basophil histamine release by protamine: a new role for a polycation recognition site

Protamine is an arginine-rich basic polypeptide that stimulates histamine release from rat mast cells but not from human basophils. In this report, we show that protamine causes a non-cytolytic potentiation of IgE-mediated histamine release from human basophils. A direct effect of protamine on basophils was supported by results obtained using cell preparations containing 35-65% basophils. The potentiation occurred at all concentrations of antigen that initiated release and was most pronounced at antigen concentrations that alone stimulated minimal histamine release. The kinetics of potentiated release were parallel to those for IgE-mediated histamine release, and addition of protamine did not overcome the block caused by antigenic desensitization. Staging experiments indicated that enhancement occurred only when protamine and antigen were added together in a single step reaction. Protamine also potentiated release stimulated by eosinophil granule major basic protein or poly-L-lysine, but inhibited release initiated by poly-L-arginine; poly-L-arginine stimulated release was also inhibited by polymyxin B. Arginine-rich histone mimicked the protamine effect, while lysine-rich histone, polymyxin B, and compound 48/80 had minimal or no effect on IgE-mediated release. These results suggest that a polycation recognition site on human basophils similar to that described for rat mast cells may mediate potentiation of basophil secretory events by arginine-rich basic polypeptides.     

Interferon-alpha/beta inhibits IgE-dependent histamine release from rat mast cells.

Although mast cells and interferons are both involved in numerous immune and inflammatory responses, little is known about how microenvironmental factors such as interferons (IFNs) influence mast cell function. To study this question, sensitized peritoneal mast cells (greater than 98% purity) obtained from rats infected 4 weeks earlier with the parasite Nippostrongylus brasiliensis were preincubated for 24 hr with rat IFN-alpha/beta in RPMI-1640, then stimulated to degranulate with worm antigens. In the absence of antigen, IFN-alpha/beta had no noticeable effect on histamine release. However, in the presence of antigen, IFN-alpha/beta (150-1500 U/ml) inhibited histamine release in a dose-dependent manner (22.2 +/- 7.5% to 56.3 +/- 6.9%, n = 10). This inhibitory effect was neither heat (56 degrees for 1 hr) nor acid (pH 2 for 18 hr) labile, but was completely blocked by anti-IFN antibodies. In the presence of compound 48/80 (1 microgram/ml) or substance P (5 X 10(-5) M), IFN-alpha/beta was ineffective at modulating histamine release. Histamine release induced by antigen in the presence of the membrane phospholipid phosphatidyl-serine (30 micrograms/ml) was inhibited by IFN in a dose-dependent manner, but maximal inhibition (25.3 +/- 2.7%, n = 10) was reached at a lower concentration of IFN (750 U/ml) than when antigen was used alone. Therefore, rat IFN-alpha/beta appears to inhibit histamine release from rat mast cells in a dose- and stimulus-dependent manner and may do so by reducing the fluidity of the cell membrane.     

Effect of azelastine on the release and action of leukotriene C4 and D4

The effect of azelastine on the release of leukotriene C4 and D4 (LTC4 and LTD4), and the antagonistic action of the drug against the leukotrienes were determined by using in vitro tests and compared with those of ketotifen and chlorpheniramine. Azelastine inhibited LTC4 and LTD4 release from guinea pig lung fragments passively sensitized with homologous anti-ovalbumin IgGl-b antibody. The 50% inhibitory concentration (IC50) of azelastine was 6.4 X 10(-5) M for a 15-min preincubation or 4.7 X 10(-5) M for a 30-min preincubation. Ketotifen and chlorpheniramine were inhibitory only at the highest concentration tested (3 X 10(-4) M), giving inhibitions of 35.6 and 21.3%, respectively. Azelastine also inhibited calcium ionophore A23187-induced release of leukotrienes from human polymorphonuclear leukocytes; the IC50 values were 3.6 X 10(-5) M for 15 min and 2.3 X 10(-6) M for 30 min of preincubation. Ketotifen and chlorpheniramine were inhibitory only after a 30-min preincubation, with IC50 values of 2.1 X 10(-5) and 5.9 X 10(-5) M, respectively. The potent inhibition by azelastine might be partly a result of the inhibition of 5-lipoxygenase, since 5-hydroxyeicosatetraenoic acid formation in rat basophilic leukemia cell homogenate was inhibited by azelastine. Pretreatment of guinea pig ileum with azelastine antagonized LTC4- and LTD4-induced contraction of the ileum with IC50 values of 7.0 X 10(-6) and 1.1 X 10(-5) M, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antiallergic Effect of Epinastine (WAL 801 CL) on Immediate Hypersensitivity Reactions: (I) Elucidation of the Mechanism for Histamine Release Inhibition

Abstract

Epinastine caused an inhibition of histamine release from rat peritoneal mast cells induced by both antigen-antibody reaction and compound 48/80. Epinastine was similarly effective in inhibiting compound 48/80-induced histamine release not only from isolated rat peritoneal mast cells but also from rat mesenterial pieces. Also, histamine release from lung pieces obtained from actively sensitized guinea pigs after exposure to antigen challenge was markedly inhibited by epinastine. The drug was effective in inhibiting not only Ca²⁺ uptake into lung mast cells in actively sensitized guinea pigs but also Ca²⁺ release from the intracellular Ca store of rat peritoneal mast cells exposed to both compound 48/80 and substance P. No significant changes were observed in phosphodiesterase activity in rat peritoneal mast cells treated with epinastine, while adenylate cyclase activity was augmented by epinastine. Epinastine has no inhibitory effect on histamine release induced by Ca²⁺ or IP3 from permeabilized mast cells. However, the drug significantly and dose-dependently suppressed calmodulin activity suggesting that histamine release inhibition due to epinastine may be partly attributable to Ca²⁺-calmodulin dependent process(es). The drug caused no visible changes in thermodynamic behavior of lipids, either in order parameter or in differential scanning calorimetry, indicating that the drug has no influence on membrane fluidity.     

Differential release of histamine and prostaglandin D2 in rat peritoneal mast cells activated with peptides

Rat peritoneal mast cells co-cultured with mouse 3T3 fibroblasts (MC/3T3) are fully responsive to immunologic stimuli. To assess their nonimmunologic activation MC/3T3 were challenged with various peptides. Optimal concentrations of substance P (10(-4) M) and bradykinin (5 x 10(-5) M) induced histamine release of 58.2 +/- 9.3 and 66.8 +/- 6.6%, respectively, while neurotensin (10(-4) M) released only 16.6 +/- 3.7% histamine. Freshly isolated mast cells (F-MC) challenged with the same concentrations of peptides released lower percentages of histamine (substance P 45.6 +/- 5.1%, bradykinin 32.5 +/- 5.3%, neurotensin 11.3 +/- 6.0%). In both MC/3T3 and F-MC, only minute amounts of prostaglandin D2 (PGD2) were produced. In contrast, activation with anti-IgE antibodies and compound 48/80 caused both histamine release and PGD2 generation. Compound 48/80-stimulated MC/3T3 and F-MC released 80.2 +/- 3.4 and 51.8 +/- 6.2% histamine, respectively, and produced 15.4 +/- 2.8 ng/10(6) mast cells and 3.9 +/- 1.4 ng/10(6) mast cells PGD2, respectively. These findings indicate that peptides and bradykinin induce selective release of histamine with no PGD2 production in both F-MC and MC/3T3. Moreover, MC/3T3 preserve their functional characteristics of connective tissue mast cells since they are fully responsive to these peptides as F-MC.     

N-Formylmethionyl-leucyl-phenylalanine: Different releasing effects on human neutrophils and rat mast cells

N-Formylmethionyl-leucyl-phenylalanine (FMLP) is a synthetic chemotactic peptide which induced β-glucuronidase and lysozyme release from human neutrophils treated with cytochalasin B. FMLP-releasing effects were rapid and dose dependent. Unlike other secretagogues of neutrophils (e.g., zymosan and immune complexes), FMLP secretory activity was not modulated by acetylcholine, which by itself did not release lysosomal enzymes from human neutrophils. Isolated rat mast cells did not respond to FMLP, which has been demonstrated to release histamine from human neutrophils. Two markers of rat mast cell secretory granules, histamine and β-glucuronidase, were assayed, but the results were negative for both. In the same experimental conditions, 48/80 released histamine and the enzyme: the ratio of the net percentage release of β-glucuronidase to the net percentage release of histamine was ～-0.4.