Abstract

BACKGROUND: Prostaglandin (PG) D2 is a potent bronchoconstrictor mediator and is found, together with leukotriene (LT) D4, in bronchoalveolar lavage fluid during the early response to allergen challenge in asthmatic subjects. The potency of PGD2 has not been established in normal and atopic non-asthmatic subjects, nor has the contribution of cholinergic mechanisms to PGD2 induced bronchoconstriction in normal subjects. Mediators released simultaneously may interact, so the effect of pre-inhalation of LTD4 on PGD2 responsiveness was investigated. METHODS: Six normal and six atopic non-asthmatic subjects performed histamine and PGD2 challenges on separate occasions. Eight normal subjects performed PGD2 challenges immediately before and 45 minutes after inhalation of 200 micrograms oxitropium bromide or placebo. Bronchial responsiveness to PGD2 was established in six normal subjects immediately after pretreatment with saline or non-bronchoconstricting doses of methacholine or LTD4 (challenge 1), and again at six hours (challenge 2). All studies were performed in a double blind, randomised, crossover fashion. RESULTS: PGD2 was 25-fold and 18-fold more potent as a bronchoconstrictor than histamine in atopic non-asthmatic and normal subjects, respectively. Responsiveness (PC35sGaw) to histamine and PGD2 correlated significantly (r = 0.917, n = 12, p < 0.001). Oxitropium bromide in a dose of 200 micrograms inhibited PGD2 induced bronchoconstriction by 37.5%, although in two of these subjects no inhibition was seen. Pre-inhalation of LTD4 and methacholine shifted the dose-response curve of PGD2 to the left by 4.6-fold and 2.4-fold, respectively. CONCLUSIONS: PGD2 is a potent bronchoconstrictor in normal subjects, which is partly mediated by cholinergic mechanisms in some subjects. No significant interaction was found between LTD4 and PGD2 in six normal subjects.