Activity of rapidly-adapting receptors to histamine and antigen challenge before and after sodium cromoglycate.

Sodium cromoglycate (SCG) blocks histamine release from sensitized mast cells challenged by antigen in vitro. Yet, not all the observed effects of SCG in vivo can be explained by this mechanism alone. Rapidly-adapting or "irritant" receptors (RAR) are thought to mediate reflex bronchoconstriction. Others have proposed that SCG may desensitize these receptors to histamine. We administered aerosols of histamine (100 micrograms/ml given for 3 min) before and after SCG (20 mg/ml aerosol for 5 min) to adult, mongrel dogs. SCG did not reduce the increase in tracheal pressure or RAR activity in response to histamine challenge. We also administered aerosols of Ascaris suum antigen (7 min) to dogs which had shown a positive skin reaction to subepidermal injection of this antigen. SCG attenuated both the increase in tracheal pressure and RAR nerve activity in response to the antigen challenge. These findings suggest that SCG does not affect the activity of the RAR or decrease the tracheal pressure in response to histamine challenge in an anesthetized dog, whereas SCG is effective in decreasing the response of both these parameters to antigen challenge when given prophylactically presumably by stabilizing the mast cell membrane.