Production of early and late pulmonary responses with inhaled leukotriene D4 in allergic sheep

Some allergic sheep respond to inhalation of antigen with both immediate and late increases in airflow resistance (late response). The mechanism of the late response is unknown but recent evidence suggests that the initial generation of slow-reacting substance of anaphylaxis (SRS-A) immediately after antigen challenge is a necessary pre-requisite for the physiologic expression of this late response. Based on this evidence we hypothesized that airway challenge with leukotriene D₄ (LTD₄), an active component of SRS-A would produce acute and late airway responses in allergenic sheep similar to those observed with antigen. In five allergic sheep with documented early and late pulmonary responses to antigen, inhalation of leukotriene D₄ aerosol (delivered dose {mean ±SE} 0.55±0.08 ug) resulted in significant early and late increases in specific lung resistance (SR_L). In three allergic sheep which only demonstrated acute responses to antigen, LTD₄ aerosol (delivered dose 0.59±0.09ug) only produced an acute increase in SR_L. In the late responders pretreatment with aerosol cromolyn sodium (1 mg/kg) did not affect the acute response but blunted the late increase in SR_L. Pretreatment with aerosol FPL-57231 (1% w/v solution) completely blocked both the acute and late responses. These data support the hypothesis that initial release of LTD₄ in the airways of sensitive animals is important for the physiologic expression of the late response.     

Differences in airway responsiveness to leukotriene D4 in allergic sheep with and without late bronchial responses

Allergic sheep respond to inhaled Ascaris suum antigen with either acute and late bronchial obstructions (dual responders) or only acute bronchoconstriction (acute responders). In this study we tested the hypothesis that one factor which may distinguish between these two populations is the difference in sensitivity to a specific mediator of airway anaphylaxis, leukotriene (LT) D4 (a major component of slow reacting substance of anaphylaxis). We postulated that if the hypothesis was correct then dual responders should demonstrate increased airway responses to inhaled LTD4 and that this increased responsiveness should also be reflected by a more severe response to inhaled antigen. To test this we used animals from both groups with the same degree of non-specific airway responsiveness to carbachol and determined their airway responses to controlled inhalation challenges with synthetic LTD4 and Ascaris suum antigen. Airway responsiveness to carbachol was determined by measuring the change in specific lung resistance (SRL) to increasing concentrations of carbachol aerosol, and then identifying, by linear interpolation, the provocative carbachol concentration which produced a 150% increase (PC150) in SRL. Airway responses to LTD4, and antigen were determined by measuring the percentage change in SRL after a controlled inhalation challenge with either aerosol. Airway responsiveness to carbachol was not different between the two groups. There was, however, a difference (p less than 0.05) in the airway response to the same dose of LTD4 in the two groups. Dual responders showed a 297 +/- 72% increase in SRL as compared to a 90 +/- 13% increase in SRL in the acute responders. Dual responders also showed a greater immediate and more prolonged response to antigen than did acute responders. These results suggest that increased responsiveness to LTD4 may be one factor which may distinguish dual responders from acute responders.     

The effect of an orally active leukotriene (LT) D4 antagonist WY-48, 252 on LTD4 and antigen-induced bronchoconstrictions in allergic sheep

In this study we examined the effects of a new orally active leukotriene (LT) D4 receptor antagonist, WY-48,252 (1,1,1-trifluoro-N-[3-(2-quinolinylmethoxy)phenyl]methanesulfonamide), on LTD4-induced bronchoconstriction and antigen-induced early and late responses in allergic sheep. For all studies WY-48,252 10 mg/kg, was administered via intragastric tube 1 h prior to airway challenge. In seven sheep, airway challenge with LTD4 [delivered dose mean +/- SE, 53 +/- 2 micrograms] resulted in an immediate increase in SRL to 600 +/- 18% over baseline. When these same sheep were treated with WY-48,252, airway challenge with LTD4 (delivered dose, 61 +/- 5 micrograms) resulted in only a 220 +/- 50% increase in SRL (p less than 0.05 vs placebo). The drug had no effect on baseline SRL. WY-48,252 was also effective in reducing early responses and blocking late responses to inhaled antigen in allergic sheep (n = 7). In the control trial, airway challenge with Ascaris suum antigen resulted in immediate and late (i.e. 6-8 h) increases in SRL of 499% and 138% over baseline (both responses, p less than 0.05). When these same sheep were pretreated with WY-48,252 the immediate antigen-induced increase in SRL was 171% and the late response was 49% over baseline (both responses p less than 0.05 vs control). These results indicate that WY-48,252 is a LTD4 antagonist in allergic sheep. The ability of this compound to modify antigen-induced early responses and to block antigen-induced late responses suggests that the generation of LTD4 during airway anaphylaxis contributes to both responses.     

Late phase bronchial obstruction following nonimmunologic mast cell degranulation

Immunologic degranulation of airway mast cells after antigen inhalation produces early and late airway obstructions in allergic sheep. In this study we determined whether nonimmunologic degranulation of airway mast cells by inhalation of compound 48/80 had similar effects. In five sheep, pulmonary flow resistance (RL), thoracic gas volume (Vtg), and arterial O2 tension (Pao2) were determined prior to and at predetermined times after inhalation of 48/80 aerosol. Immediately after challenge mean specific lung resistance (sRL = RL X Vtg) increased by 259% and mean Pao2 decreased by 29%. All values returned to normal by 3 h. By 5-h postchallenge sRL again increased significantly; this second increase in sRL (92% above base line) was maximal at 7 h and was accompanied by a 17% drop in Pao2. In these same sheep inhalation of Ascaris suum antigen produced comparable early changes in sRL, but the onset of the late response was somewhat delayed and more pronounced. In a second group of sheep (n = 5), pretreatment with the mast cell stabilizer cromolyn sodium prevented both early and late responses by compound 48/80. Pretreatment with the histamine H1-antagonist chlorpheniramine had no significant effect on either response, whereas pretreatment with FPL 55712, an antagonist of slow-reacting substance of anaphylaxis (SRS-A), slightly but not significantly attenuated the early response and completely prevented the late response. We conclude that, like immunologic stimuli, nonimmunologic mast cell degranulation produces early and late bronchial obstructions in allergic sheep; that these responses are mediator dependent; and that while histamine and SRS-A contribute to the early response, it is the early appearance of SRS-A which is an important prerequisite for the late response.     

The effect of an orally active leukotriene (LT) antagonist YM-16638 on antigen-induced early and late airway responses in allergic sheep

In this study we examined the effects of an orally active leukotriene (LT) antagonist YM-16638 [[5-[[3-(4-acetyl-3-hydroxy-2-propyl-phenoxy)propyl]thio]-1,3,4- thiadiazol-2-yl]thio] acetic acid on antigen-induced early and late responses in allergic sheep. For all studies YM-16638 was administered via intragastric tube 1 h before airway challenge with Ascaris suum antigen. Six allergic sheep were challenged on four occasions (2 control and 2 drug trials) each greater than or equal to 14 days apart and the tests were conducted in the following order: control-1; YM-16638 30 mg/kg; control-2; YM-16638 10 mg/kg. Specific lung resistance (SRL) was used as an index of the airway response to antigen and was measured before and serially after antigen challenge. In both control trials antigen challenge resulted in significant early and late airway responses (i.e. increases in SRL); however, there was a significant difference between the peak late increases of SRL in control-1 (206%) and control-2 (115%) suggesting a carry-over effect of the 30 mg/kg dose of YM-16638. At both doses, YM-16638 reduced the early response and blocked the late response when compared to either control trial. These results suggest that sulfidopeptide LTs contribute to both antigen-induced early and late airway responses in allergic sheep.     

The effect of an orally active leukotriene D4/E4 antagonist, LY171883, on antigen-induced airway responses in allergic sheep

Leukotriene (LT) D4 is a putative mediator of allergic asthma: inhaled LTD4 produces early and late increases in specific lung resistance (SRL) and slows tracheal mucus velocity (TMV) similar to inhaled antigen. In this study we examined the effects of an orally active LTD4/LTE4 antagonist, LY171883 [1-less than 2-Hydroxy-3-propyl-4-less than 4-(1H-Tetrazol-5-yl) Butoxy greater than Phenyl greater than Ethanone], on early and late changes in SRL and TMV following airway challenge with Ascaris suum antigen in conscious allergic sheep. SRL and TMV were measured before and up to 8 h and 24 h after antigen challenge after either LY171883 (30 mg/kg, p.o. 2 h before challenge) or placebo pretreatment. After placebo pretreatment antigen challenge resulted in significant early (483% over baseline) and late (221% over baseline) increases in SRL (n = 9). LY171883 pretreatment, however, significantly reduced the early increase in SRL (163% over baseline) and blocked the late response. LY171883 did not prevent the antigen-induced fall in TMV from 5-8 h post challenge (n = 6), but TMV recovered more rapidly in the drug trial returning to baseline values by 24 h. These results suggest that the generation of LTD4, and its metabolite LTE4, during airway anaphylaxis contributes to the early increase in SRL and is important for eliciting the late increase in SRL as well as contributing to the fall in TMV.     

A possible role for PAF in allergen-induced late responses: modification by a selective antagonist

We determined whether platelet-activating factor (PAF) plays a role in allergen-induced airway responses by studying the effects of a selective PAF antagonist WEB-2086 on antigen-induced early and late airway responses in allergic sheep. In seven sheep, inhaled Ascaris suum produced significant early (282%) and late (176%) increases in specific lung resistance (sRL). WEB-2086 (1 mg/kg iv) given 20 min before antigen challenge did not affect the early response, but the peak late increase in sRL was only 37% over base line (P less than 0.05 vs. control). To study the mechanism by which PAF contributes to antigen-induced responses, we evaluated the effects of pharmacological probes on PAF-induced bronchoconstriction. Inhaled PAF (dose range 75-700 micrograms) caused reproducible (r = 0.781, P less than 0.05) increases in sRL in eight sheep. The PAF-induced bronchoconstriction was blocked by WEB-2086 (1 mg/kg iv) and by the leukotriene antagonist FPL-55712 (30 mg by aerosol); however, neither the cyclooxygenase blocker indomethacin (2 mg/kg iv) nor the histamine H1-antagonist chlorpheniramine (2 mg/kg iv) blocked the PAF response. WEB-2086, however, did not block bronchoconstriction induced by aerosol leukotriene D4, indicating that PAF acts indirectly through leukotrienes. Finally, we determined whether PAF could induce late airway responses. Inhaled PAF produced an immediate increase in sRL in all seven sheep tested, but late airway responses were observed in only three of the seven sheep.(ABSTRACT TRUNCATED AT 250 WORDS)     

Late-phase bronchial vascular responses in allergic sheep

Sheep were classified on the basis of their airway response to Ascaris suum antigen aerosols as allergic or nonsensitive. Allergic sheep were classed as acute or dual responders. Acute responders had only an immediate increase in mean airflow resistance after antigen, whereas dual responders had an immediate and late-phase (6-8 h after antigen challenge) increase in mean airflow resistance; nonsensitive sheep had minimal airway responses to antigen (less than 30% increase from base line). The sheep were anesthetized 2 wk later and, after a left thoracotomy, were challenged with antigen to determine bronchial vascular responses; bronchial artery blood flow was measured with an electromagnetic flow probe. Airway responses to antigen aerosol challenge were similar in the anesthetized and conscious animals. The mean fall in bronchial vascular resistance (BVR) immediately after antigen challenge was similar in acute and dual responders (41 +/- 7 and 47 +/- 9% of base line, respectively). In dual responders, late-phase airway responses were preceded by a significant increase from base line in Qbr and a fall in bronchovascular resistance (BVR). The mean fall in BVR 6-8 h after antigen challenge in documented dual responders was significantly different from bronchial vascular responses in acute responders (59 +/- 3 vs. 89 +/- 10%, respectively). Sheep without airway responses to A. suum had no significant changes in bronchial hemodynamics or airways mechanics. Late-phase-associated changes in BVR are a specific response to antigen challenge and may be a sensitive index of mediators being released.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of leukotriene D4 on mucociliary and respiratory function in allergic and nonallergic sheep

We determined the effect of aerosol challenge with leukotriene D4 (LTD4) on specific lung resistance (sRL) and tracheal mucous velocity (TMV) in conscious sheep with (allergic) and without (nonallergic) Ascaris suum hypersensitivity. In allergic sheep LTD4 in concentrations of 50, 100, and 150 micrograms/ml produced dose-dependent increases in mean sRL by 44 (P = NS), 154 (P less than 0.05), and 233% (P less than 0.05), respectively. The increase in sRL produced by 150 micrograms/ml LTD4 was prevented by FPL 55712, an antagonist of slow-reacting substance of anaphylaxis. In nonallergic sheep 150 micrograms/ml LTD4 failed to elicit a significant change in sRL. In contrast to the changes in airway mechanics, concentrations of LTD4 as low as 25 micrograms/ml produced significant decreases in TMV in allergic sheep. The maximum decrease in TMV at this dose occurred 2 h after challenge; with larger doses of LTD4 (100 and 150 micrograms/ml) the maximum effect was observed 3 h after challenge. Furthermore, 150 micrograms/ml LTD4 reduced TMV in nonallergic sheep (mean decrease 43%, P less than 0.05). FPL 55712 only had a minor effect on the LTD4-induced decreases in TMV. We conclude that allergic sheep exhibit greater airway responsiveness to inhaled LTD4 than nonallergic sheep but that this difference is not evident for the concomitant changes in mucociliary transport. This suggests that the allergic state is associated with an increased responsiveness to LTD4 in tissues controlling airway caliber but not in those contributing to mucociliary function.     

Separation of late bronchial responses from airway hyperresponsiveness in allergic sheep

Allergic sheep with antigen-induced early and late responses were used to determine whether airway hyperresponsiveness (AHR) to carbachol is present during the late response and whether blocking the late response with the leukotriene D4 (LTD4) antagonist MK-571 also blocks this AHR. To do this, we first showed that MK-571 blocked the antigen-induced late response, and then, in a separate study, we determined the effect of MK-571 treatment on airway responsiveness 6 h after antigen challenge (at the start of the late response). MK-571 (5 mg, by metered dose inhaler) given 30 min before and 4 h after Ascaris suum challenge had no effect on the acute response to antigen but blocked (P less than 0.05) the late response compared with placebo (n = 7). In the second study (n = 6), the antigen-induced acute increases in mean specific lung resistance (sRL) were also similar in the placebo (249%) and drug trials (247%). By 6 h postchallenge, however, mean sRL in the placebo trial began to increase (54%, P less than 0.05), whereas in the drug trial mean sRL was baseline. Nevertheless, AHR was apparent in both trials as indicated by a mean twofold leftward shift in the dose-response curves to inhaled carbachol (P less than 0.05 vs. prechallenge). Bronchoalveolar lavage at 6 h showed that MK-571 did not prevent the inflammatory cell influx into the lung. These observations suggest that although LTD4 may be a mediator of the late response in sheep, it is not a primary mediator affecting cholinergic AHR during this period.     

Ciliary responsiveness in allergic and nonallergic airways

Allergic asthma is associated with airway (smooth muscle) hyperresponsiveness to several chemical mediators of anaphylaxis; however, it is not known whether this is accompanied by mucociliary hyperresponsiveness. The purpose of this study was therefore to determine if airway ciliary activity, a component function of mucociliary clearance, exhibits exaggerated responses to prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), and leukotriene D4 (LTD4) in allergic sheep when compared with nonallergic sheep, and the effects of LTD4 are direct or involve the generation of cyclooxygenase products of arachidonate metabolism. Ciliary beat frequency (CBF) was measured in a perfusion chamber with a microscopic technique using tracheal epithelial cells obtained from brushing of "allergic" (positive cutaneous reaction and previous bronchospastic response to inhaled specific antigen) and "nonallergic" (negative cutaneous reaction, no previous inhalation challenge with antigen) sheep. Mean base-line CBF was not different among the groups; PGE1, PGE2, and LTD4 induced dose-dependent increases in CBF, and these increases were not different in allergic and nonallergic sheep. At the highest agonist concentration the mean increase in CBF from base line varied between 13 and 16% (P less than 0.05). The ciliostimulatory effect of LTD4 was significantly blunted by both the sulfidopeptide leukotriene antagonist FPL-55712 and the cyclooxygenase inhibitor indomethacin. These results suggest that allergic sheep fail to exhibit ciliary hyperresponsiveness to selected chemical mediators of anaphylaxis and the ciliostimulatory effect of LTD4 depends on the activation of cyclooxygenase and possibly the generation of prostaglandins.     

Inhibition of allergic late airway responses by inhaled heparin-derived oligosaccharides.

Inhaled heparin has been shown to inhibit allergic bronchoconstriction in sheep that develop only acute responses to antigen (acute responders) but was ineffective in sheep that develop both acute and late airway responses (LAR) (dual responders). Because the antiallergic activity of heparin is molecular-weight dependent, we hypothesized that heparin-derived oligosaccharides (<2, 500) with potential anti-inflammatory activity may attenuate the LAR in the dual-responder sheep. Specific lung resistance was measured in 24 dual-responder sheep before and serially for 8 h after challenge with Ascaris suum antigen for demonstration of early airway response (EAR) and LAR, without and after treatment with inhaled medium-, low-, and ultralow-molecular-weight (ULMW) heparins and "non-anticoagulant" fractions (NAF) of heparin. Airway responsiveness was estimated before and 24 h postantigen as the cumulative provocating dose of carbachol that increased specific lung resistance by 400%. Only ULMW heparins caused a dose-dependent inhibition of antigen-induced EAR and LAR and postantigen airway hyperresponsiveness (AHR), whereas low- and medium-molecular-weight heparins were ineffective. The effects of ULMW heparin and ULMW NAF-heparin were comparable and inhibited the LAR and AHR even when administered "after" the antigen challenge. The ULMW NAF-heparin failed to inhibit the bronchoconstrictor response to histamine, carbachol, and leukotriene D(4), excluding a direct effect on airway smooth muscle. In six sheep, segmental antigen challenge caused a marked increase in bronchoalveolar lavage histamine, which was not prevented by inhaled ULMW NAF-heparin. The results of this study in the dual-responder sheep demonstrate that 1) the antiallergic activity of inhaled "fractionated" heparins is molecular-weight dependent, 2) only ULMW heparins inhibit the antigen-induced EAR and LAR and postantigen AHR, and 3) the antiallergic activity is mediated by nonanticoagulant fractions and resides in the ULMW chains of <2,500.     

Indomethacin and FPL-57231 inhibit antigen-induced airway hyperresponsiveness in sheep

We compared the development of antigen-induced airway hyperresponsiveness (AHR) 24 h after challenge with Ascaris suum antigen in allergic sheep with acute (n = 7) and with dual (n = 7) airway responses and then attempted to modify this AHR. Cholinergic airway responsiveness was determined by measuring the carbachol dose required to increase specific lung resistance (sRL) 150% (i.e., PC150). Subsequently the sheep were challenged with antigen and sRL was measured at predetermined times to document the presence or absence of a late response. PC150 was redetermined 24 h later followed by bronchoalveolar lavage (BAL) to assess inflammation. Only dual responders developed AHR (PC150 decreased, P less than 0.05). There were no significant differences in BAL between the two groups. Six dual responders were then, on separate occasions (greater than or equal to 3 wk), pretreated with placebo, indomethacin (2 mg/kg iv), or a leukotriene antagonist, FPL-57231 (30 mg inhaled). Neither agent significantly affected the acute response to antigen. Only FPL pretreatment blocked the late response, but both agents blocked the antigen-induced AHR 24 h later. BAL at 24 h showed no significant differences. These results indicate that only dual responders develop AHR 24 h after antigen challenge. This AHR appears independent of the late increase in sRL or the severity of pulmonary inflammation. AHR appears to be sensitive to agents that interfere with the early release or actions of cyclooxygenase and lipoxygenase metabolites in dual responders.     

Antigen stimulates glycoprotein secretion and alters ion fluxes in sheep trachea

We studied the effects of in vitro challenge with specific antigen (Ascaris suum antigen) on glycoprotein secretion and ion fluxes in tracheal tissues from allergic sheep. We mounted tissues in Perspex chambers and measured secretion of 35S- and 3H-labeled glycoproteins and fluxes of Cl- and Na+. In tissues from allergic sheep, A. suum antigen (25 micrograms protein X ml-1) increased glycoprotein secretion. A. suum antigen initially reversed net Cl- flux, causing net absorption of Cl- and of Na+. This was followed 15-30 min later by net secretion of Cl- and of Na+. Pretreatment of tissues with cromolyn (10(-4) M) greatly reduced the effects of A. suum antigen but did not abolish them. The cromolyn-resistant effects were nonspecific, because they were similar to those of in vitro challenges with nonspecific proteins, ovalbumin and ragweed in allergic sheep, and A. suum antigen in nonallergic sheep. We conclude that challenge with A. suum antigen results in mucus hypersecretion in airways of allergic sheep, by both specific and smaller nonspecific effects. Specific effects (cromolyn sensitive) are produced by mediators which are released from airway cells in response to A. suum challenge.     

Nedocromil sodium in allergen-induced bronchial responses and airway hyperresponsiveness in allergic sheep

We examined the effects of nedocromil sodium, a new drug developed for the treatment of reversible obstructive airway disease, on allergen-induced early and late bronchial responses and the development of airway hyperresponsiveness 24 h after challenge in nine allergic sheep. On occasions greater than 2 wk apart the sheep were treated with 1) placebo aerosol (buffered saline) before and 3 h after antigen challenge, 2) an aerosol of nedocromil sodium (1 mg/kg in 3 ml buffered saline) before antigen challenge and placebo 3 h after challenge, and 3) placebo aerosol before and nedocromil sodium aerosol 3 h after challenge. Early and late bronchial responses were determined by measuring specific lung resistance (sRL) before and periodically after challenge. Airway responsiveness was assessed by determining from dose-response curves the carbachol concentration (in % wt/vol) that increased sRL to 5 cmH2O/s. In the placebo trial, antigen challenge resulted in early and late increases in sRL over a base line of 353 +/- 32 and 131 +/- 17% (SE), respectively. Both early and late increases in sRL were blocked (P less than 0.05) when the sheep were pretreated with nedocromil sodium. When nedocromil was given after the early response, the late response was reduced significantly. Eight of nine sheep developed airway hyperresponsiveness 24 h after antigen challenge. In these eight sheep, carbachol concentration before antigen challenge was 2.6 +/- 0.3%, 24 h later carbachol concentration was significantly lower (1.8 +/- 0.3%). Both nedocromil sodium treatments blocked (P less than 0.05) this antigen-induced airway hyperresponsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antigen sensitization and methacholine responses in dogs with hyperreactive airways

Antigen sensitization was induced in six Basenji-Greyhound (BG) dogs by weekly aerosol exposure to Ascaris suum. The effects on airway responsiveness to inhaled methacholine were studied before and at least 2 wk following Ascaris sensitization. All dogs developed detectable serum levels of Ascaris-specific immunoglobulin E (IgE), and five out of six dogs developed airway responsiveness to antigen over the 4- to 6-mo period. This was accompanied by a decrease rather than an increase in airway responsiveness to inhaled methacholine. When dogs were challenged with methacholine 30 min after Ascaris antigen aerosol challenge, however, dogs reactive to Ascaris became hyperresponsive to methacholine. The magnitude of the response to antigen correlated (r = 0.85) inversely with the dose of methacholine increasing pulmonary resistance 200%. These data show that in BG dogs airway responsiveness to methacholine is increased by acute antigen exposure but that sensitization of previously unsensitized dogs does not increase nonspecific airway responsiveness.     

Modification of bronchial blood flow during allergic airway responses

Ascaris suum antigen effects on mean airflow resistance (RL) and bronchial arterial blood flow (Qbr) were studied in allergic anesthetized sheep with documented airway responses. Qbr was measured with electromagnetic flow probes, and supplemental O2 prevented antigen-induced hypoxemia. Aerosol challenge with this specific antigen increased RL and Qbr significantly. Cromolyn sodium aerosol pretreatment prevented antigen-induced increases in RL but not in Qbr. Intravenous cromolyn, however, prevented increases in Qbr and RL, suggesting a role for mast cell degranulation in both bronchomotor and bronchovascular responses to antigen. Antigen-induced increases in Qbr were not solely attributable to histamine release. Indomethacin pretreatment attenuated the antigen-induced increase in Qbr, thus suggesting that vasodilator cyclooxygenase products contribute to the vascular response. Antigen challenge significantly decreased Qbr after indomethacin and metiamide pretreatment, which suggests that vasoconstrictor substances released after antigen exposure also modulate Qbr; however, released vasodilators overshadow vasoconstrictor effects. Thus antigen challenge affects Qbr by locally releasing histamine and vasodilator prostaglandins as well as vasoconstrictor substances. These effects were independent of antigen-induced changes in systemic and pulmonary hemodynamics.     

Late pulmonary responses induced by Ascaris allergen in conscious squirrel monkeys

This study presents an antigen-dependent model of biphasic pulmonary changes to Ascaris suum in conscious squirrel monkeys. Animals with strong positive skin reactivity towards A. suum were trained to sit quietly in chairs and to breathe through face masks. Dynamic compliance (Cdyn) and pulmonary resistance (RL) were measured in these conscious animals before and for a period of 11 h after administration of an aerosol of Ascaris or ragweed antigen. The aerosol of Ascaris antigen induced reproducible increases (42%) in RL (P less than 0.001) and decreases (17%) in Cdyn (P less than 0.01) that peaked respectively 5 and 35 min after antigen challenge and lasted 60-90 min. After recovery, a second bronchoconstriction began between 2 and 8 h and peaked between 4 and 10 h after antigen challenge. Decreases in Cdyn (41%) were significantly greater (P less than 0.003) whereas mean increases in RL (44%) were similar during the late phase as compared with the first phase. The mean Cdyn decreases lasted a minimum of 2 h, whereas RL increases lasted less than 60 min. The time course of the responses varied from animal to animal but changes in individual animals were reproducible over a period of 6 mo. No significant correlation was observed between the cutaneous and the pulmonary responses to Ascaris and the late response was not reversed by aerosol administration of salbutamol (1.0 mg/ml). As a negative control animals were exposed to an aerosol of ragweed extract after which no immediate or late pulmonary response were observed. The results suggest that this primate model may be useful to study the pathophysiology of asthma in humans.     

Central role of cyclooxygenase in the response of canine peripheral airways to antigen

We studied the effects of antigen aerosol challenge on the airways of the canine peripheral lung and examined the roles of cyclooxygenase products, histamine, and cholinergic activity in the responses. One-minute deliveries of 1:10,000 or 1:100,000 concentrations of Ascaris suum antigen aerosol through a wedged bronchoscope resulted in mean maximal increases in collateral system resistance (Rcs) of 415 and 177%, respectively, after 4-8 min. Repeated antigen challenge (1:100,000) resulted in significantly decreased responsiveness to antigen after the initial exposure (P less than 0.005). Bronchoalveolar lavage fluid obtained from the isolated, challenged segment had a significant increase in mean (+/- SE) prostaglandin D2 (PGD2) concentration vs. control (222.0 +/- 65.3 vs. 72.7 +/- 19.5 pg/ml; P less than 0.05); histamine concentrations were variable and not significantly different (4.1 +/- 2.6 vs. 1.2 +/- 0.2 ng/ml; P greater than 0.05). In nine experiments, cyclooxygenase inhibition significantly attenuated the antigen-induced increase in Rcs by 53.4% (P less than 0.001), and the concentration of PGD2 in lavage fluid was reduced by 96.0% (P less than 0.01). Blockade of histamine H1-receptors (n = 8) or cholinergic receptors (n = 7) did not significantly affect the airway response (P greater than 0.05). These data indicate that the canine peripheral lung responds in a dose-dependent manner to antigen aerosol challenge and exhibits characteristics of antigen tachyphylaxis. Results also suggest that cyclooxygenase products play a central role in the acute bronchoconstrictive response of the lung periphery.     

Immunologic mast cell-mediated responses and histamine release are attenuated by heparin.

Heparin has been shown to act as a competitive inhibitor of inositol 1,4,5-triphosphate (InsP3) receptors in various cell types. Because InsP3 is one of the second messengers involved in stimulus-secretion coupling in mast cells, it is possible that heparin may inhibit mast cell-mediated reactions. Therefore, in allergic sheep, we tested this hypothesis in two mast cell-mediated reactions induced by immunologic and nonimmunologic stimuli: immediate cutaneous reaction (ICR) and acute bronchoconstrictor response (ABR). In 12 sheep allergic to Ascaris suum antigen, the surface area of the skin wheal was determined 20 min after intradermal injection (0.05 ml) of increasing concentrations of specific antigen, compound 48/80, and histamine, without and after pretreatment with heparin (100, 300, or 1,000 U/kg i.v.). Antigen, compound 48/80, and histamine produced concentration-dependent increases in ICR. Heparin "partially" inhibited the ICR to antigen and compound 48/80 in a dose-dependent manner without modifying the ICR to histamine. The heparin preservative benzyl alcohol was ineffective. In 11 additional sheep, specific lung resistance was measured before and after inhalation challenges with antigen, compound 48/80, and histamine without and with aerosol heparin pretreatment (1,000 U/kg). Heparin blocked the antigen- and compound 48/80-induced bronchoconstriction without modifying the airway effects of histamine. In isolated human uterine mast cells, heparin inhibited the anti-immunoglobulin E- but not the calcium ionophore- (A23187) induced histamine release. These data suggest that heparin inhibits the ICR and ABR induced by stimuli that produce immunologic and nonimmunologic mast cell degranulation without attenuating the effects of histamine.(ABSTRACT TRUNCATED AT 250 WORDS)