Studies on the mechanism of drug-induced bronchiolar relaxation in the guinea pig

Relaxation of bronchiolar smooth muscle of the guinea pig was demonstrated with isoproterenol, epinephrine, theophylline, sodium nitrite, ACTII, and glucagon. The order of molar potency was isoproterenol > epinephrine > ACTH = glucagon > theophylline > sodium nitrite. Relaxation by isoproterenol and epinephrine could be blocked completely by pronethalol, while that of ACTH was moderatedly reduced by the blocking agent. Drug effects appeared to be unchanged when glucose was omitted from the incubation medium. After extended exposure to epinephrine, the smooth muscle was unresponsive to all drugs tested. Acetate addition failed to alter responsiveness, but the addition of glucose for 45 minutes prior to drug exposure restored the ability of the tissue to respond to all drugs, although the magnitude of the response was markedly reduced. These data indicate that glyeogenolysis may play a role in drug-induced smooth muscle relaxation.