An experimental asthma model in unanesthetized rat, and the difference in effect of disodium cromoglycate between passive cutaneous anaphylaxis model and asthma model in rat

We established here the experimental asthma model in unanesthetized rat, based on the observation of breathing. The effect of disodium cromoglycate (DSCG) was compared between the passive cutaneous anaphylaxis (PCA) model in rat and our experimental asthma model. The systemic anaphylaxis was elicited, in the rat passively sensitized with reaginic antibodies (reagin) against DNP-As, in response to challenge with antigen. The longer duration of expiration than that of inspiration was observed in the thoracic breathing of antigen-treated rats. The proportion of animals showing this respiratory distress in thoracic breathing (RDTB) was related to the concentration of antiserum used for the sensitization. The relation between RDTB and the concentration of antiserum was more manifest when the degree of RDTB was considered as a score. Inhibition of DSCG was dose-dependent on RDTB and reagin-induced PCA at more than 1 mg/kg. The maximal inhibition of DSCG (20 mg/kg, i.v.) on RDTB or PCA was observed when it was given 30 s before the challenge with antigen. The effect on RDTB decreased gradually with time after dose, and lasted beyond 60 min similar to the inhibitory activity of DSCG on antigen-induced asthmatic reaction in patients. Whereas, the effect on PCA decreased rapidly, and disappeared within 30 min after dose. These results indicate that RDTB is a principal indicator of respiratory distress induced by reagin, and that the effect of DSCG in asthmatics may be explained by its inhibitory activity on RDTB rather than that on PCA.