Inhibition of bronchial hyperresponsiveness to histamine induced by intravenous administration of leukotriene C4 by novel thromboxane A2 receptor antagonists ONO-NT-126 and ONO-8809 in guinea-pigs

Effect of prostaglandin E2 on eicosanoid release by human bronchial biopsy specimens from normal and inflamed mucosa

BACKGROUND

Eicosanoids such as prostaglandin E2 (PGE2), thromboxane A2 (TXA2), and peptidoleukotrienes (pLT) are known to be biologically highly active lipid mediators, especially in human lung epithelium. PGE2 is thought to have mostly bronchoprotective effects, whereas pLT and TXA2 are bronchoconstrictive. This study was undertaken to assess the release and interaction of eicosanoids in human bronchial biopsy specimens of normal and inflamed mucosa.

METHODS

Bronchial biopsy specimens were obtained from 16 patients, seven controls without signs of inflammation and nine patients with severe inflammatory processes in the epithelium. The release of pLT, TXA2 (measured as TXB2), and PGE2 was investigated using a "functional in vitro test" and the addition of several stimuli.

RESULTS

Specimens incubated with arachidonic acid released higher amounts of pLT, TXB2, and PGE2 than unstimulated specimens. Preincubation with PGE2 revealed significant inhibition of arachidonic acid-induced release of pLT and TXB2 (> 50%). The inhibitory effect was higher in normal than in inflamed epithelium.

CONCLUSIONS

Exogenous PGE2 has inhibitory effects on the release of pLT and TXB2 in human bronchial biopsy specimens. This finding could explain the bronchoprotective effect of inhaled PGE2 in normal subjects and asthmatic subjects as direct eicosanoid interactions. It also supports the concept of PGE2 as a bronchoprotective endogenous substance. The complex effects of PGE2 as a modulating mediator in inflammation may be worth investigating.

Inhibition by a novel peptide leukotriene receptor antagonist ONO-1078 of airway wall thickening and airway hyperresponsiveness to histamine induced by leukotriene C4 or leukotriene D4 in guinea-pigs

We studied the effect of intravenous administration of leukotriene (LT) C4 or LTD4 on airway responsiveness to histamine and airway wall thickening in guinea-pigs. Guinea-pigs were killed and the lungs were fixed in formalin. Slides from paraffin-embedded section of the lungs were stained and the airways that were cut in transverse section were measured by tracing enlarged images using a digitizer. Moreover, airway resistance (Raw) was determined by a pulmonary mechanics analyser and we calculated two indices, an index of airway wall thickening and the one of airway hyperresponsiveness to histamine, from changes of baseline-Raw and peak-Raw following intravenous administration of histamine before and after the intravenous administration of LTC4 or LTD4. The infusion of LTC4 or LTD4 induced an increase of the relative thickness of the airway wall in peripheral bronchi demonstrable by the histological examination. In analysis of airway function, intravenous administration of LTC4 or LTD4 induced airway hyperresponsiveness to histamine with airway wall thickening. The LTC4 and LTD4 receptor antagonist ONO-1078 inhibited these effects of LTC4 and LTD4, suggesting LTC4 and LTD4 may induce airway wall thickening and airway hyperresponsiveness through LTC4 and LTD4 receptors in the airways.

Inhibition by thromboxane antagonists of airway hyperresponsiveness to histamine induced by 13,14-dihydro-15-keto-PGF2 alpha in guinea-pigs

We studied the effect of intravenous administration of 13,14-dihydro-15-keto-prostaglandin (PG) F2 alpha on airway responsiveness to histamine and airway wall thickening in guinea-pigs. Guinea-pigs were killed and the lungs were fixed in formalin. Slides from paraffin-embedded sections of the lungs were stained and the airways that were cut in transverse section were measured by tracing enlarged images using a digitizer. Moreover, airway resistance (Raw) was determined by a pulmonary mechanics analyser and we calculated two indices, an index of airway wall thickening and the one of airway hyperresponsiveness to histamine, from changes of baseline-Raw and peak-Raw following intravenous administration of histamine before and after the intravenous administration of 13,14-dihydro-15-keto-PGF2 alpha. Intravenous administration of 10 micrograms/kg 13,14-dihydro-15-keto-PGF2 alpha for 1 h did not induce an increase of the relative thickness of the airway wall by the histological examination. In analysis of airway function, intravenous administration of 10 micrograms/kg 13,14-dihydro-15-keto-PGF2 alpha for 1 h induced airway hyperresponsiveness to histamine without airway wall thickening. Thromboxane A2 (TXA2) receptor antagonists ONO-NT-126 and ONO-8809 inhibited the 13,14-dihydro-15-keto-PGF2 alpha-induced airway hyperresponsiveness to histamine, suggesting that the effect of 13,14-dihydro-15-keto-PGF2 alpha on bronchial hyperresponsiveness is likely to be mediated through TXA2.