Hydrocortisone and isoproterenol effects on trachealis cAMP and relaxation

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Abstract
Isoproterenol concentration-response curves for cAMP formation and relaxation were determined in control and hydrocortisone-treated strips of canine tracheal smooth muscle. cAMP formation and muscle relaxation were well correlated, and both responses were enhanced proportionally by hydrocortisone treatment. cGMP was unchanged by isoproterenol but was increased to a small but significant extent by hydrocortisone. Prostaglandin E2 (not a .beta.-adrenergic agonist) relaxed the muscle strips, but this effect was not enhanced by hydrocortisone pretreatment. cAMP is evidently an obligatory intermediate in the chain of events by which .beta.-adrenergic agonists relax airway smooth muscle. The action of hydrocortisone on this process is localized at or before cAMP formation, since it enhanced both cAMP formation and relaxation to the same extent.