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

Abstract

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 β-adrenergic stimulation/α-adrenergic inhibition in airway conductance (G aw) and dynamic lung compliance (C DYN) were observed. For both N and S dogs, thymoxamine pretreatment served to enhance an isoproterenol inhibition of PGF 2α-induced G aw decreases. No effect was observed in C DYN. 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 α-adrenergic agents failed to produce bronchospasm; however, propranolol/indomethacin pretreatment significantly potentiated the effects of all three α-agents. No significant changes were observed in the C DYN response either prior to or after pretreatment with propranolol/indomethacin. In contrast, for S dogs, all three α-agonists produced moderate bronchoconstriction with or without propranolol/indomethacin pretreatment. In addition, the G aw 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 C DYN response in the S group of animals. These data suggest the presence of α-adrenergic influence in the canine airways and elaboration of this action appears to occur best in propranolol/indomethacin-pretreated animals.