A NEW BIOASSAY TO STUDY CONTRACTILE AND RELAXANT EFFECTS OF PGE(2) ONPERFUSED GUINEA-PIG TRACHEA

The aim of this study was to investigate the effects of PGE(2) under d ifferent experimental conditions. By a newly developed imaging bioassa y system, changes of the diameter of isolated perfused guinea-pig trac heal tubes were continuously measured. The results were compared with those of a conventional ring bioassay system. The effect of PGE(2) was examined in epithelium-intact and -denuded tubes. The potency of PGE( 2) applied to the inner surface of tube preparations was significantly enhanced by about six-fold in epithelium-denuded compared with epithe lium-intact tubes. In rings there was no difference. The results sugge st a potential role of epithelium in assessment of airway reactivity i n vivo. The study demonstrates, that the effects of PGE(2) depend crit ically on the experimental approach. PGE(2) (0.01 nmol 1(-1)-1 mu mol 1(-1)) contracted tracheal tubes, but resulted in relaxation of ring p reparations under basal tone. The spontaneous tone of guinea pig trach ea can be reduced with the cyclooxygenase inhibitor diclofenac. Pretre atment of the rings with diclofenac reversed the relaxation into contr action. Preincubation of tube preparations with diclofenac had no effe ct on basal tone, indicating that there was no inherent spontaneous pr ostanoid-dependent tone or the mediators may be washed out at a relati vely fast rate and, therefore, tone may not be apparent. (C) 1996 Else vier Science Inc.