Leukotriene D4 potentiates histamine-induced bronchoconstriction in guinea-pigs

Mast cell mediators in citric acid-induced airway constriction of guinea pigs

We demonstrated previously that mast cells play an important role in citric acid (CA)-induced airway constriction. In this study, we further investigated the underlying mediator(s) for this type of airway constriction. At first, to examine effects caused by blocking agents, 67 young Hartley guinea pigs were divided into 7 groups: saline + CA; methysergide (serotonin receptor antagonist) + CA; MK-886 (leukotriene synthesis inhibitor) + CA; mepyramine (histamine H1 receptor antagonist) + CA; indomethacin (cyclooxygenase inhibitor) + CA; cromolyn sodium (mast cell stabilizer) + CA; and compound 48/80 (mast cell degranulating agent) + CA. Then, we tested whether leukotriene C4 (LTC4) or histamine enhances CA-induced airway constriction in compound 48/80-pretreated guinea pigs. We measured dynamic respiratory compliance (Crs) and forced expiratory volume in 0.1 s (FEV0.1) during either baseline or recovery period. In addition, we detected histamine level, an index of pulmonary mast cell degranulation, in bronchoalveolar lavage (BAL) samples. Citric acid aerosol inhalation caused decreases in Crs and FEV0.1, indicating airway constriction in the control group. This airway constriction was significantly attenuated by MK-886, mepyramine, cromolyn sodium, and compound 48/80, but not by either methysergide or indomethacin. Both LTC4 and histamine infusion significantly increased the magnitude of CA-induced airway constriction in compound 48/80-pretreated guinea pigs. Citric acid inhalation caused significant increase in histamine level in the BAL sample, which was significantly suppressed by compound 48/80. These results suggest that leukotrienes and histamine originating from mast cells play an important role in CA inhalation-induced noncholinergic airway constriction.

Prednisone pretreatment leads to histaminic airway hyporeactivity soon after resolution of the immediate allergic response

We assessed the effect of prednisone pretreatment (50 mg/day for three days) on the development of the early increase in histamine reactivity that occurs soon after resolution of the immediate response in allergic humans. Four allergic subjects who were known to develop only isolated immediate responses upon Kentucky bluegrass inhalation, as well as four mild allergic asthmatic subjects known to develop typical dual phase responses, were evaluated. All testing was done more than nine weeks after the grass pollen season had ended. Allergen inhalation produced an immediate response in all subjects. However, upon resolution of the immediate response to allergen in these pretreated subjects, the PC200His in all dual responding asthmatics and in three of the four isolated immediate responders had substantially increased above baseline values. We conclude that prednisone pretreatment leads to histaminic hyporeactivity soon after resolution of the immediate allergic response in both dual responding asthmatics and isolated immediate responders. It would seem that this prednisone effect is independent of its potential influence on the influx of inflammatory cells into diseased airways.

Lipoxygenase metabolites mediate increased airways responsiveness to histamine after acute platelet activating factor exposure in the guinea-pig

Platelet activating factor (Paf, 0.02 micrograms/kg, i.v. bolus) caused an acute increase in airways responsiveness to histamine in anaesthetized guinea-pigs prepared for recording airways resistance (RL) and dynamic compliance (Cdyn). Aspirin pretreatment (10 mg/kg, i.v.) attenuated the return of airways responsiveness to prechallenge levels. Pretreatment with the combined cyclooxygenase/lipoxygenase inhibitors BW 755C (20 mg/kg, i.v.) and ETYA (20 mg/kg, i.v.), or with the putative cysteinyl-containing leukotriene antagonist FPL 55712 (0.25 mg/kg/min, i.v.), or a Paf antagonist SRI 63441 (2.5 mg/kg, i.v.), prevented Paf-induced increased airways responsiveness. Inhibitors of leukotriene synthesis, BW 755C and ETYA, or action, FPL 55712, had variable effects on Paf-induced bronchoconstriction. These data suggest that lipoxygenase metabolites, possibly leukotrienes, may mediate an acute increase in airways responsiveness to histamine after Paf exposure.

Bronchial reactivity increases soon after the immediate response in dual-responding asthmatic subjects

To determine whether bronchial reactivity is augmented soon after an allergen-induced immediate asthmatic response, we compared reactivity to histamine before and immediately upon resolution of the immediate asthmatic response in seven subjects with mild asthma who were known to develop dual asthmatic responses after inhalation of Kentucky bluegrass allergen. Using a body plethysmograph and quiet breathing technique, specific airway resistance (SRaw) and reactivity to aerosol histamine were assessed on two days prior to allergenic challenge. The dose of histamine that doubled SRaw (PC200His) was determined by interpolation from histamine dose-response curves. On the day of allergenic challenge, each subject inhaled a concentration that was sufficient to induce a dual asthmatic response. Upon resolution of the immediate asthmatic response (45 to 105 minutes) after allergen, the PC200His in all cases had decreased more than 50 percent of its original value (PC200His for the group was 0.29 +/- 1.42 mg/ml [mean +/- SE], compared to 0.84 +/- 1.23 mg/ml initially). Seven or more days after the allergen, each subject had a PC200His comparable to original values. Our data indicate that airway reactivity in dual-responding asthmatic subjects markedly increases soon after the immediate asthmatic response and much before the late asthmatic response manifests clinically. Whether this early increase in bronchial reactivity is a putative requirement for, or shares common characteristics with the late asthmatic response requires further study.

Effects of a thromboxane synthetase inhibitor (OKY-046) and a lipoxygenase inhibitor (AA-861) on bronchial responsiveness to acetylcholine in asthmatic subjects

The effect of a selective thromboxane synthetase inhibitor, OKY-046, and a selective 5-lipoxygenase inhibitor, AA-861, on bronchial responsiveness to acetylcholine was studied in 23 asthmatic subjects. The provocative concentration of acetylcholine producing a 20% fall in forced expiratory volume in one second (PC20 FEV1) was measured before and after oral administration of OKY-046 (3000 mg over four days) and AA-861 (1100 mg over four days) and inhalation of OKY-046 (30 mg) in 10, 10, and nine asthmatic subjects respectively. Baseline values of FEV1 and forced vital capacity (FVC) were not altered by oral OKY-046, oral AA-861, or inhaled OKY-046. The geometric mean value of PC20 FEV1 increased significantly from 0.55 to 2.24 mg/ml after oral OKY-046, but was unchanged after inhalation of OKY-046 and after oral administration of AA-861. These results suggest that thromboxane A2 may play a part in bronchial hyperresponsiveness to acetylcholine.

Human small airway smooth muscle responses in vitro; actions and interactions of methacholine, histamine and leukotriene C4

The in vitro contractile responses to methacholine, histamine and leukotriene C4 (LTC4) were measured in human bronchiolar strips obtained after surgery. LTC4 was approximately 100 times more potent than both methacholine and histamine (mean pD2 values were 8.01, 6.18 and 5.87 respectively). All three agonists produced the same maximum contractile response (Tmax) and no difference was found in the time course of methacholine-, histamine- and LTC4-induced responses. When methacholine, histamine and LTC4 were applied in succession on one airway preparation, no interactions between these agonists were demonstrated for pD2. However, interactions were found concerning Tmax. The sensitivity (pD2) could be measured accurately and reproducibly and showed a relatively small within-patients variation (coefficients of variation 4-5%). In contrast, Tmax showed a considerable within-patients variation (coefficients of variation 47-91%), which limits its usefulness when small numbers of airway preparations are studied.

Aerosolized and intravenously administered leukotrienes: effects on the bronchoconstrictor potency of histamine in the guinea-pig

The effects of leukotrienes C4 and D4 (LTC4 and LTD4), administered intravenously or by aerosol, on the bronchoconstrictor potency of intravenously administered histamine have been investigated in anaesthetized, mechanically ventilated guinea-pigs. LTC4 (2 nM) had no effect on either the EC50 or the maximum contractile response to histamine on the isolated trachea of the guinea-pig. At 10 nM, LTC4 induced a rightward shift in the histamine concentration-response curve without affecting the maximum response. LTD4 (0.05-0.20 nmol kg-1, i.v.) dose-dependently enhanced histamine (9-36 nmol kg-1, i.v.)-induced increases in airways resistance, whereas equibronchoconstrictor doses of LTC4 (0.1-0.4 nmol kg-1, i.v.), failed to enhance histamine-induced increases in airways resistance. Aerosols of LTC4 and LTD4 generated from solutions of 1-16 microM and administered for 30 s, elicited concentration-dependent bronchoconstrictions comprising decreases in dynamic compliance and increases in airways resistance. At 20 min after exposure to these aerosols, the potency of histamine (9-36 nmol kg-1, i.v.) was significantly increased on both airways resistance and dynamic compliance. The potentiation induced by LTC4 (4 microM, 30 s) was maintained up to 60 min after aerosol exposure whereas that induced by LTD4 (4 microM, 30 s) was maintained up to 40 min after aerosol exposure but was not significantly different (P greater than 0.05, unpaired Student's t test) to saline-exposed animals at 60 min. LTC4 as has been previously reported for LTD4, does not enhance the histamine-induced contraction of isolated airways smooth muscle. In contrast to LTD4, intravenously administered LTC4 does not appear to enhance histamine-induced bronchoconstriction. On the other hand, aerosols of either LTC4 or LTD4 potentiate histamine in vivo in a concentration-dependent manner. These data suggest that leukotrienes may contribute to the regulation of airways reactivity to histamine in the guinea-pig.

Involvement of capsaicin-sensitive afferent neurones in a vagal-dependent interaction between leukotriene D4 and histamine on bronchomotor tone

Leukotriene D4 (LTD4, 0.1-0.5 micrograms/kg, i.v.), administered 20 s before histamine (H, 1-4 micrograms/kg, i.v.), enhanced the bronchoconstrictor response to H by between 105 and 168%. Bilateral vagotomy, atropine or indomethacin each attenuated, whereas hexamethonium completely prevented, this enhancement. LTD4 failed to enhance the bronchoconstrictor effects of either acetylcholine (ACh) or electrical stimulation of the vagi. Capsaicin pretreatment reduced bronchoconstrictor responses to electrical stimulation of the vagi, but did not affect depressor responses. There was no interaction between LTD4 and H on bronchomotor tone in capsaicin-pretreated guinea-pigs. It is concluded that LTD4 enhances H-induced bronchoconstriction by a mechanism which involves an increased activity of efferent cholinergic nerves innervating the airways. However, the failure of LTD4 to enhance bronchoconstriction due to ACh or vagal stimulation, together with the prevention of the interaction between LTD4 and H by capsaicin-pretreatment, suggests that the site of the interaction may be on capsaicin-sensitive afferent neurones.