Immunologic and Neuropharmacologic Stimulation of Mucous Glycoprotein Release from Human Airways In Vitro

Abstract

Human bronchial airways obtained after surgical resection were maintained in tissue culture for 24-48 h. Incorporation of [³H]- or [¹⁴C]-glucosamine, [¹⁴C]threonine, or Na₂[³⁵S]O₄ to the culture media resulted in biosynthesis of two radiolabeled glycoproteins—one filtering in the exclusion volume of Sepharose 2B, and the other filtering with an approximate molecular weight of 400,000. Both fractions had similar elution patterns from DEAE-cellulose anion exchange chromatography. [³H]Glucosamine was incorporated equally into the two fractions. The effects of anaphylaxis, histamine, and several neurohormones upon the release of [³H]glucosamine-labeled glycoproteins were analyzed, making no attempt to separate the two glycoprotein fractions. Three lines of evidence were found suggesting that mast-cell degranulation increases mucous release from cultured airways. (a) Supernatant fluids from anaphylaxed peripheral human lung that contained 200-400 ng/ml histamine and 400-1,000 U/ml slow-reacting substance of anaphylaxis (SRS-A) increased release by 40±18%. (b) The addition of antigen to IgE-sensitized airways led to the release of 26±7% of the total histamine and a 36±14% increase in mucous release. (c) Reversed anaphylaxis with anti-IgE antibodies induced a 36±6% release of histamine from the airways and an increase in the release of mucous glycoproteins of 25±9%. Exogenous histamine added to airways increased mucous glycoprotein release, an effect prevented by cimetidine, an H-2 antagonist. Selective histamine H-2, but not H-1 agonists increased mucous glycoprotein release, suggesting the possibility that anaphylaxis of airways results in increased mucous glycoprotein release partly through histamine H-2 stimulation. A cholinomimetic agonist, methacholine, increased mucous release; this response was prevented by atropine which alone had no effect. No response to β-adrenergic stimulation with either isoproterenol or epinephrine was noted. However, α-adrenergic stimulation with either norepinephrine combined with propranolol or phenylephrine alone resulted in dose-related increases in glycoprotein release. Both α-adrenergic and cholinergic stimulation of human tissues induce the formation of guanosine 3′,5′-phosphoric acid (cyclic GMP), and 8-bromo cyclic GMP added to the airways led to increased mucous secretion. Thus, it seems likely that neurohormones capable of stimulating cyclic GMP formation in human airways may lead to increased mucous glycoprotein release.