INCREASED RESPONSE TO ANTIGEN AND HISTAMINE-RELEASE IN SMALLER SENSITIZED CANINE BRONCHI

We studied the Schultz-Dale response in vitro in large and small size branches from 3rd to 6th generation bronchi from ragweed-sensitized do gs. The response to electric field stimulation (EFS) increased after a ntigen from 65.56 +/- 8.11 to 78.6 +/- 9.0 mN/mm(2) of smooth muscle ( P < 0.01), but no topographical difference was observed. The response to ragweed (% of the response to EFS) was 158.3 +/- 12 and 67.1 +/- 11 .7 in strips from small and large branches respectively (P < 0.01), wh ile no difference was observed between generations; when clustering br onchi according to dimension, it was 129.9 +/- 13.4 in small and 71.9 +/- 19.8 in large bronchi (P < 0.01). Histamine released from small an d large branches was 2.90 +/- 1.01 and 0.76 +/- 0.20 (ng/mg of tissue) respectively (P < 0.05); no difference was found between generations. In conclusion, in sensitized dogs a greater response to antigen, whic h involves a higher histamine release, occurs in small compared to lar ge bronchi. We suggest that control of distribution of ventilation occ urs mainly at, small bronchi level, which becomes the elective tissue to study the Schultz-Dale response. Finally, the classification of bro nchi into generations is inadequate to study allergic bronchospasm.