This study has compared the abilities of isoproterenol and forskolin to inhibit immunologic- and nonimmunologic-induced histamine release from guinea-pig superfused trachea and enzymatically dispersed tracheal cells. Contraction was also measured in the former preparation. The potency of isoproterenol was similar for inhibition of all parameters associated with immunologic (ovalbumin) challenge in the two preparations. In contrast, forskolin appeared less potent in inhibiting ovalbumin-induced histamine release from dispersed tracheal cells. Histamine release by the nonimmunologic secretagogues d-tubocurarine and compound 48/80 was not altered by either substance. However, inhibition by isoproterenol and forskolin of tracheal contraction was evident when challenge was conducted with d-tubocurarine and compound 48/80. Inhibition of contraction appears to be a result of functional antagonism at the level of the smooth muscle. The superfused trachea is a useful preparation in which to explore the effects of substances that modulate mast cell mediator release.
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