Muscarinic hyperresponsiveness of antigen-sensitized feline airway smooth muscle in vitro.
OBJECTIVE
To determine the effect of in vivo antigen sensitization (Ascaris suum) of cats on tracheal smooth muscle (TSM) and bronchial smooth muscle (BSM) muscarinic reactivity in vitro.


METHODS
Healthy domestic shorthair cats of either sex.


METHODS
Cats were sensitized and were long-term antigen (or sham) challenge exposed for 6 weeks by aerosolization with soluble Ascaris suum. Tracheal and BSM preparations were obtained and stimulated in vitro by electrical field stimulation (EFS), acetylcholine (ACh, a muscarinic agonist), and physostigmine (an AChase inhibitor). Responses were compared with responses of comparable tissues from sham antigen challenge-exposed cats.


RESULTS
Tracheal and BSM from sensitized, compared with sham-sensitized (control), cats had greater isometric contraction (expressed as percentage of the response observed for isotonic, 63 mM KCl-elicited contraction [% KCl]) in response to endogenous (EFS) and exogenous muscarinic receptor activation (ACh). Contractions in response to EFS by TSM from control cats were 74% KCl vs 97% KCl for antigen-sensitized TSM (P < 0.04). Muscarinic responses were augmented comparably by in vivo sensitization; TSM from control cats contracted to 190% KCl vs 230% KCl (P < 0.03) for TSM from immune-sensitized cats. Physostigmine augmented responses of all tissues to ACh so that TSM from control (290% KCl) and antigen-sensitized (257% KCl) cats were similar. Responses of BSM from antigen-sensitized cats had similar augmentation of contractile response to EFS and ACh.


CONCLUSIONS
Long-term in vivo antigen sensitization increases numbers of muscarinic receptors on airway smooth muscle or decreases the availability or activity of AChase in cats.


CONCLUSIONS
Modulation of muscarinic receptors may be useful for treatment of asthmatic cats with in vivo airway hyperreactivity.
Mitchell
R W
RW
Department of Medicine, Physiologic and Pharmacologic Sciences, University of Chicago, IL 60637, USA.
Ndukwu
I M
IM
Leff
A R
AR
Padrid
P A
PA
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D000947:Antigens, Helminth / Q000276:immunology; D017165:Ascaris suum / Q000276:immunology; D001980:Bronchi / Q000187:drug effects* / Q000502:physiology; D002415:Cats / Q000502:physiology*; D002800:Cholinesterase Inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D066298:In Vitro Techniques; D007428:Intradermal Tests / Q000662:veterinary; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D010830:Physostigmine / Q000494:pharmacology*; D011976:Receptors, Muscarinic / Q000032:analysis / Q000187:drug effects / Q000502:physiology; D014132:Trachea / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology
D000947:Antigens, Helminth; D002800:Cholinesterase Inhibitors; D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D010830:Physostigmine; D000109:Acetylcholine