Bronchodilating activity of forskolin in vitro and in vivo

The effect of forskolin, a receptor-independent adenylate cyclase activator on acetylcholine (ACh)-, histamine- and leukotriene D4 (LTD4)-induced contractions in isolated tracheal spirals was investigated. Forskolin reduced the contraction due to these agonists (IC50S: ACh 5.8 X 10(-6) M; histamine 4 X 10(-7) M; LTD4 3.1 X 10(-6) M). Forskolin was also effective against ACh- and histamine-induced contraction when added during contraction. In ovalbumin-sensitized guinea pigs, intravenously and intraduodenally administered forskolin significantly reduced the bronchospasm due to aerosol administration of ovalbumin. These results suggest that forskolin could prove useful in delineating the role of cyclic nucleotides in pulmonary smooth muscle responses.