Effects of methacholine, histamine and atropine on pulmonary guanosine-3', 5'-monophosphate levels in hypersensitive mice

Abstract

Pulmonary levels of cGMP and cAMP in mice sensitized to methacholine and histamine with B. pertussis were examined to determine whether sensitization could be the result of an alteration in the metabolism of these cyclic nucleotides. The results presented show that in sensitized mice, methacholine raised cGMP to levels that were about double those produced without sensitization. In analogous experiments, histamine raised cGMP by approximately 100% in sensitized mice without producing significant increases in nonsensitized groups. Atropine completely blocked the cGMP rises produced by methacholine but did not eliminate those produced by histamine, thus indicating that cholinergic, but not the histaminergic elevation of cGMP involves activation of muscarinic receptors. The influence of pertussis on cAMP appeared to be opposite in direction from cGMP, i.e., a small but significant drop in cAMP levels was found following methacholine administration to sensitized, but not to nonsensitized mice. It was concluded that pertussis sensitization increases the responsiveness of the pulmonary guanylate cyclase-cGMP system to methacholine and histamine, and that the altered patterns of cGMP accumulation may contribute to the biochemical mechanism of sensitization.