Comparative effects of SCH 1000 and fenoterol after histamine-induced bronchoconstriction in asymptomatic asthmatics

In 16 asymptomatic asthmatics a functional study was carried out under controlled conditions during histamine bronchial provocation test (HBPT) and after bronchodilation test with either SCH 1000 or fenoterol by evaluating both SRAW and the slope of the alveolar plateau of nitrogen washout curve (N2 ph III). During HBPT, 9 of 16 subjects showed a central response (increase in RAW and SRAW only), whereas in the remaining 7 subjects histamine induced a mixed response due to an increase in both SRAW and N2 ph III. No differences between the two groups were observed in age and functional data during controlled conditions. Doses of delivered histamine were not significantly different. In 5 of 9 central responders to HBPT, SCH 1000 induced a decrease in SRAW only, whereas in 3 of the remaining 4 fenoterol caused both central and peripheral bronchodilation (decrease in both SRAW and N2 ph III). All mixed responders to HBPT showed a mixed bronchodilation during SCH 1000 (three subjects) or fenoterol (the remaining four). These data seem to indicate that the mechanism of bronchodilation induced by SCH 1000 is related to that of histamine-induced bronchoconstriction. Moreover, bronchodilation due to fenoterol could be related to a vagal modulation or be a systemic direct effect.