Release of slow-reacting substance of anaphylaxis from layers of guinea pig aorta

Release of slow-reacting substance of anaphylaxis (SRS-A) from layers of ovalbumin-sensitized guinea pig aorta after antigenic challenge in vitro was investigated. SRS-A was determined by bioassay and in terms of leukotriene C4-like immunoreactivity using radioimmunoassay. While no SRS-A could be detected before challenge, the adventitia released considerable amounts of SRS-A after addition of antigen to the incubation medium. On the other hand, an inner layer of the aortic wall consisting of smooth muscle tissue with some adherent endothelium released only small amounts of SRS-A after challenge.     

Release of slow-reacting substance of anaphylaxis from layers of guinea pig aorta

Release of slow-reacting substance of anaphylaxis (SRS-A) from layers of ovalbumin-sensitized guinea pig aorta after antigenic challenge in vitro was investigated. SRS-A was determined by bioassay and in terms of leukotriene C₄-like immunoreactivity using radioimmunoassay. While no SRS-A could be detected before challenge, teh adventitia released considerable amounts of SRS-A after addition of antigen to the incubation medium. On the other hand, an inner layer of the aortic wall consisting of smooth muscle tissue with some coherent endothelium released only small amounts of SRS-A after challenge.     

Purification and some physicochemical properties of slow-reacting substance of anaphylaxis (SRS-A) from sensitized guinea pig lung.

The slow-reacting substance of anaphylaxis (SRS-A) generated by antigen challenge of sensitized guinea pig lung fragments was partially purified and the physicochemical properties of this activity were studied. The SRS-A recovered from antigen challenged lung preparations of 600 animals was used for the purification procedure. Treatment with organic solvents, extraction with 80% ethanol, Sephadex LH-20 chromatography with 80% ethanol, and DEAE-Sephadex A-25 chromatography in 60% methanol eluted with 0.0 to 0.1 M NaCl in 60% methanol was the purification sequence finally adopted. Overall recovery of SRS-A bioactivity was 60% with a specific activity of 2.52 units/ng of dry weight. This represented a 1.67 million-fold purification over the starting material. The DEAE-Sephadex A-25 step alone provided a 7600-fold purification. This highly purified SRS-A had an apparent molecular weight of 380 to 400 daltons. The bioactivity was acid labile and alkaline stable and was blocked by low concentrations of the SRS-A antagonist FPL 55712. The SRS-A was thermostable in aqueous media and displayed enhanced bioactivity after heating at 60 C for 60 min. These results indicate that we have developed a highly efficient new approach to the isolation of guinea pig SRS-A, which also may be useful in the study of SRS-A from other tissues or species. The physicochemical properties of guinea pig SRS-A appear to be very similar to those of SRS-A from other species.     

Release of slow-reacting substance of anaphylaxis and leukotriene C4-like immunoreactivity from guinea pig colonic tissue

Colonic mucosa, muscularis propria and subserosa from ovalbumin-sensitized guinea pigs were incubated and challenged with antigen in vitro. Slow-reacting substance of anaphylaxix (SRS-A) was determined biologically as well as radioimmunologically in terms of leukotriene (LT) C₄-like immunoreactivity. Before antigenic challenge release of immunoreactive LTC₄ by all tissues was below or close to the detection limit of the radioimmunoassay. After addition of antigen colonic mucosa released considerable amounts of LTC₄-like immunoreactivity, while muscularis propria and subserosa were less active. The biological activity of the SRS-A formed after challenge was antagonized by FPL 55712. Contrary to LTC₄-like immunoreactivity release of 6-keto-prostaglandin (PG) F1_α was predominant in the subsero and smaller amounts were released from the smooth muscular and mucosal layers. Synthesis of SRS-A and LTC₄-like immunoreactivity, respectively, as well as synthesis of 6-keto-PGF_1α was inhibited by the dual inhibitor of lipoxygenase and cyclooygenase BW755C. The results suggest a role for LTs as local mediators of inflammatory reactions in colonic disease states, particularly those with possible involvement of immunological processes.     

Prostaglandin release by slow reacting substance from guinea pig and human lung tissue

Slow reacting substance (SRS) injected into the pulmonary artery released prostaglandin E (PGE) and F_2α (PGF_2α) and the 15-keto-13, 14-dihydro PG metabolites from non-sensitized and ovalbumin sensitized, isolated, perfused guinea pig lungs. PGs were also released from lungs incubated with SRS. Sensitized lungs released more PGs in both types of preparations. Indomethacin inhibited the effect of SRS. Passively sensitized human lung fragments, in parallel to guinea pig lung, released PGE, PGF_2α and the metabolites when incubatted with SRS or antigen. In experiments, SRS and arachidonic acid given intravenously increased the airway insufflation pressure in anesthetized guinea pigs. These effects, but not the action of injected PGF_2α and histamine, were abolished by indomethacin. The results indicate that one of the modes of SRS action is by release of PGs, and are consistent with the hypothesis that PGs are predominantly “secondary” mediators (in the temporal sense) of the antigen-antibody reaction.     

Prostaglandin release by slow reacting substance from guinea pig and human lung tissue.

Slow reacting substance (SRS) injected into the pulmonary artery released prostaglandins E (PGE) and F2alpha (PGF2alpha) and the 15-keto-13, 14-dihydro PG metabolites from non-sensitized and ovalbumin sensitized, isolated, perfused guinea pig lungs. PGs were also released from lungs incubated with SRS. Sensitized lungs released more PGs in both types of preparations. Indomethacin inhibited the effect of SRS. Passively sensitized human lung fragments, in parallel to guinea pig lung, released PGE, PGF2alpha and the metabolites when incubated with SRS or antigen. In in vivo experiments, SRS and arachidonic acid given intravenously increased the airway insufflation pressure in anesthetized quinea pigs. These effects, but not the action of injected PGF2alpha and histamine, were abolished by indomethacin. The results indicate that one of the modes of SRS action is by release of PGs, and are consistent with the hypothesis that PGs are predominantly "secondary" mediators (in the temporal sense) of the antigen-antibody reaction.     

Structure of slow-reacting substance of anaphylaxis (SRS-A)

To elucidate the chemical structure of slow-reacting substance of anaphylaxis from rat (SRS-A^rat), SRS-A^rat were purified by the method of Orange with modification using DEAE-Sephadex A-25 chromatography. Ultraviolet absorption spectrum of purified SRS-A^rat indicated the presence of conjugated triene. Arylsulfatase B degradation products and HCl degradation products were subjected to analysis by a gas chromatography and mass spectrometry and a thin layer chromatography. Products obtained by arylsulfatase B catalysis contained 5,6-dihydroxy-7,9,11,14-eicosatetraenoic acid. HCl degradation products showed the presence of glycine, glutamic acid and cysteic acid. Furthermore, the analysis of anhydrous hydrazine degradation products of SRS-A^rat and of HCl hydrolyzed products of dinitrophenylated SRS-A^rat revealed the presence of glycine at C-terminal and glutamic acid at N-terminal. The study of the substrate specificity of arylsulfatase B against various materials including SRS-A^rat suggested the presence of sulfone in SRS-A^rat. The molecular ion peak of SRS-A^rat sodium salt was observed at m/e 680 in field desorption mass spectrum of SRS-A^rat.On the basis of these data, we identified the structure of SRS-A^rat as [γ-glutamyl-4(5-hydroxy-7,9,11,14-eicosatetraenoic acid-6-yl)-4,4-dioxocysteinyl] glycine.     

Calcium-induced calcium release mechanism in guinea pig taenia caeci

Fura-2 was used to measure the amount of Ca released from the intracellular Ca store of a saponin-skinned smooth muscle fiber bundle of the guinea pig taenia caeci (width, 150-250 microns) placed in a capillary cuvette at 20-22 degrees C. The amount of Ca actively loaded into the store was assayed when released by the application of 50 mM caffeine and/or 10 microM inositol 1,4,5-trisphosphate (IP3) in the absence of ATP, and was found to have a biphasic dependence on the loading [Ca2+] with a peak near pCa 6. After Ca loading at pCa 6, IP3 released almost all the releasable Ca, whereas caffeine discharged Ca from only approximately 40% of the store. The maximum amount of Ca in the store was some 220 mumol/liter cell water. Ca in the caffeine-releasable store was released approximately exponentially to zero with time when Ca2+ was applied in the absence of ATP, and the rate constant of the Ca-induced Ca release (CICR) increased steeply with the concentration of Ca2+ applied. Increase in [Mg2+] (0.5-5.0 mM) or decrease in pH (7.3-6.7) shifted the relation between pCa and the rate of CICR roughly in parallel toward the lower pCa. An adenine nucleotide increased the rate of the CICR, but it did not change the range of effective [Ca2+]. 5 mM caffeine greatly enhanced the CICR mechanism, making it approximately 30 times more sensitive to [Ca2+]. However the drug had no Ca-releasing action in the absence of Ca2+. Procaine in millimolar concentrations inhibited the rate of the CICR. These properties are similar to those of the skeletal muscle CICR and ryanodine receptor channels. Rates of the CICR under a physiological ionic milieu were estimated from the results, and a [Ca2+] greater than 1 microM was expected to be necessary for the activation of the Ca release. This Ca sensitivity seems too low for the CICR mechanism to play a primary physiological role in Ca mobilization, unless assisted by other mechanisms.     

The effect of calcium antagonists on contractions of the sensitized and normal guinea pig ileum

The purpose of this study was to learn wether a number of Ca²⁺ antagonists were effective in reducing contractile response of the isolated ileum of the sensitized and normal guinea pig. Contractions of the normal ileum in response to LTD₄, acetylcholine, histamine, and potassium chloride were obtained before and after verapamil, diltiazen and papaverine. Ovalbumin-induced contractions of the ovalbumin-sensitized ileum were obtained in the presence of the three Ca²⁺ antagonists. In the normal ileum, all the Ca²⁺ antagonists were highly effective in diminishing the contractile responses to LTD₄, acetylcholine, histamine and potassium chloride. In the sensitized ileum, ovalbumin-evoked contractions, with subsequent release of a potent contractile mediator (presumably SRS-A), were Ca²⁺-dependent since verapamil, diltiazem and papaverine caused a concentration-related reduction of contractions. Thus, the influx of extracellular Ca²⁺ plays a key role in the contractile responses of the normal and sensitized guinea pig ileum when stimulated by various potent agonists acting on specific receptors or on the cell membrane.     

Role of free cytosolic calcium in secretagogue-stimulated amylase release from dispersed acini from guinea pig pancreas

To determine the role of free cytosolic calcium ([Ca+2]i) in stimulated enzyme secretion from exocrine pancreas, we determined the effects of various pancreatic secretagogues on [Ca+2]i and amylase release in dispersed acini from the guinea pig pancreas. Cholecystokinin-octapeptide (CCK-OP), carbachol, and bombesin, but not vasoactive intestinal peptide, stimulated rapid increases in [Ca+2]i from 100 to 600-800 nM that were independent of extracellular calcium. The increases in [Ca+2]i were transient (lasting less than 5 min) and correlated with an initial rapid phase of amylase release. After 5 min, secretagogue-stimulated amylase release occurred at basal [Ca+2]i. Carbachol pretreatment of the acini abolished the effects of CCK-OP and bombesin on [Ca+2]i and the initial rapid phase of amylase release. 4 beta-phorbol 12-myristate 13-acetate (PMA) had no effect on [Ca+2]i but stimulated an increase in amylase release. The addition of CCK-OP or A23187 to PMA-stimulated acini caused an increase in [Ca+2]i and PMA-stimulated amylase release only during the first 5 min after addition of these agents. These results indicate that CCK-OP, carbachol, and bombesin release calcium from an intracellular pool, resulting in a transient increase in [Ca+2]i and that this increase in [Ca+2]i mediates enzyme secretion during the first few minutes of incubation. The results with PMA suggest that secretagogue-stimulated secretion not mediated by increased [Ca+2]i (sustained secretion) is mediated by 1,2-diacylglycerol.     

The effect of calcium antagonists on histamine and leukotriene-induced tracheal microvascular permeability in the guinea pig

The effects of several calcium antagonists, i.e., nifedipine, verapamil and 8-[N,N-diethylamino]-octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8), were evaluated in situ on agonist-induced increases in permeability of the airway microvasculature in anesthetized guinea pigs. Vascular permeability was measured as tracheal extravascular albumin content by using 125I-bovine serum albumin and the utilization of 51Cr labelled-erythrocytes to correct for blood volume. Intratracheal injections of histamine (1, 10 and 100 micrograms) or leukotriene (LT) D4 (1, 10 and 100 ng) produced dose-dependent increases in extravasated radiolabelled albumin in the trachea. Although histamine produced a greater maximal response than LTD4, the latter provocation was ten times more potent than the former. Nifedipine, a dihydropyridine calcium slow channel blocker, exhibited dose-dependent (30, 100 and 300 micrograms/kg) inhibitory activity against histamine-induced increases in extravascular albumin, while another calcium slow channel blocker, verapamil (100, 300 and 1000 micrograms/kg), exhibited much less activity. TMB-8, a purported intracellular calcium antagonist (1 and 10 mg/kg), was observed to have some inhibitory activity versus histamine. Similar doses of all three calcium antagonists failed to significantly inhibit increases in tracheal microvascular permeability evoked by LTD4. These results suggest that differences in mediator-induced microvascular permeability in the guinea pig trachea are evident depending upon the agonist selected and the pool of calcium utilized.     

Enhancement of isolated airway responses to bronchoconstrictive agonists by the slow-reacting substance of anaphylaxis antagonist FPL 55712

The activity of the SRS-A antagonist FPL 55712 against histamine, carbachol and ion-induced contraction of isolated airway smooth muscle was evaluated. FPL 55712 enhanced responses of guinea-pig trachea and parenchymal lung strips to histamine and carbachol. Enhancement was not obviously related to concentration. It is suggested that this effect may be the result of cyclo-oxygenase inhibition by FPL 55712. These observations may account for some of the anamalous findings regarding the antagonism of leukotrienes by FPL 55712 previously reported.     

Effects of several calcium antagonists and dipyridamole in the isolated perfused guinea pig heart

Three calcium (Ca) antagonists and dipyridamole were examined in the isolated perfused guinea pig heart at perfusate Ca concentrations of 1.25 and 3.75 mM. The Ca antagonists: FR 7534, nifedipine and D600 produced similar dose-dependent decreases in left ventricular dp/dt and myocardial oxygen consumption (MV?O₂) at both Ca concentrations. However, dose response curves were shifted significantly to the right by increased perfusate Ca requiring six to ten times more Ca antagonist to produce equivalent effects. Dipyridamole produced only slight negative inotropic effects which appeared to be less dependent on external Ca concentration. All four agents significantly increased coronary blood flow at 1.25 mM Ca but not at 3.75 mM Ca. The Ca antagonists decreased heart rate at 3.75 mM Ca whereas dipyridamole had strong negative chronotropic effects at both perfusate Ca concentrations. These experiments provide evidence that FR 7534 acts as a Ca antagonist. In addition, Ca antagonists of different structure had similar effects on the isolated heart distinct from those of dipyridamole.     

PAF antagonists: different effects on platelets, neutrophils, guinea pig ileum and PAF-induced vasolidation in isolated rat lung

The effects of structurally different PAF receptor blockers were investigated in platelets, neutrophils, guinea pig ileum, rat isolated lung and rat isolated pulmonary artery. PAF caused serotonin release from platelets and a characteristic shape change and adhesion of neutrophils. The antagonists (CV 3988, alprazolam, 48740 RP and Merck-Sharp and Dohme L-652, 731) inhibited platelet serotonin release but not neutrophil shape change adhesion or lysosomal enzyme release. The antagonists in high concentrations (10⁻⁵ −10⁻⁴M) inhibited nonspecifically the PAF-induced (10⁻⁸M) guinea pig ileum contraction, but were ineffective at concentrations which inhibited platelet responses. In the rat lung the compounds, in high concentrations, partially inhibited the low dose PAF-induced pulmonary vasodilation and the high dose PAF induced pulmonary vasoconstriction and edema. Our data indicate that some platelet PAF antagonists may be ineffective in blocking the action of PAF on neutrophils and smooth muscle preparations and suggest either PAF-receptor independent actions of PAF or different classes of PAF receptors.