The modulation of adrenergic airway tone in normal and ascaris-sensitive beagle dogs

The airway effects of adrenergic receptor stimulation/inhibition were investigated in sets of normal (N) and natively ascaris-sensitized (S) beagle dogs. In one group, the effect of beta-adrenergic stimulation/alpha-adrenergic inhibition in airway conductance (Gaw) and dynamic lung compliance (CDYN) were observed. For both N and S dogs, thymoxamine pretreatment served to enhance an isoproterenol inhibition of PGF2 alpha-induced Gaw decreases. No effect was observed in CDYN. In another set of animals, the effects of i.v. administration of norepinephrine (NE), epinephrine (EPI) and phenylephrine (PE), before and after pretreatment with propranolol/indomethacin were observed. For N dogs, all three alpha-adrenergic agents failed to produce bronchospasm; however, propranolol/indomethacin pretreatment significantly potentiated the effects of all three alpha-agents. No significant changes were observed in the CDYN response either prior to or after pretreatment with propranolol/indomethacin. In contrast, for S dogs, all three alpha-agonists produced moderate bronchoconstriction with or without propranolol/indomethacin pretreatment. In addition, the Gaw response to i.v. PE was statistically greater in S dogs than that observed in the N group. Finally, only i.v. PE produced significant decreases in the CDYN response in the S group of animals. These data suggest the presence of alpha-adrenergic influence in the canine airways and elaboration of this action appears to occur best in propranolol/indomethacin-pretreated animals.