Antigen-induced dyspnea in Sprague Dawley rats. Effects of local treatment with anti-asthmatic drugs.

We wanted to study the effect of anti-asthma drugs on antigen-induced dyspnea in conscious Sprague Dawley (S.D.) rats. A line of dyspnea bred rats was produced, where all immunized animals respond with dyspnea when challenged with aerosolized ovalbumin (OA). The animals were immunized intraperitoneally (i.p.) with OA (10 micrograms) together with Al(OH)3 (100 mg) and challenged 2 to 3 weeks later with OA aerosol. We examined the effects of terbutaline (TERB), disodium cromoglycate (DSCG), atropine (ATRO), theophylline (THEO), a 5-HT receptor antagonist methysergide (METH), and two glucocorticosteroids (GCS) budesonide (BUD) and dexamethasone (DEX), on this response. The drugs were given locally either by intratracheal (i.t.) instillation or by aerosol. The rats were placed one by one in an air tight box and the breathing pattern was recorded. Parameters such as time of onset of dyspnea after end of challenge (elapsed time), duration and occurrence of dyspnea, were used to quantify the response. In the vehicle- treated group nearly all animals responded to OA with signs of dyspnea. TERB was the only drug effective when given as an aerosol, whereas when given i.t., also DEX and METH inhibited the dyspnea. Dyspnea is a serious response and can only be alleviated by the most effective anti-asthma drugs.