PHYSIOLOGICAL-RESPONSES AND HISTAMINE-RELEASE AFTER NASAL ANTIGEN CHALLENGE - EFFECT OF ATROPINE

We enrolled nine allergic subjects in a double,blind, placebo-controll ed study to examine the ef feet of premedication with 0.6 mg of atropi ne on nasal antigen challenge. The challenge consisted of unilaterally stimulating the nasal septum with diluent followed by three increasin g doses of antigen and recording responses bilaterally. Sneezes, sympt oms, and nasal airway resistance (NAR) were recorded. Secretions were collected using preweighed filter paper discs and histamine was measur ed. Antigen challenge with the subjects on placebo led to significant dose-dependent increases in sneezes, symptom scores, ipsilateral and c ontralateral secretion weights, ipsilateral NAR, and total amount of i psilateral histamine (p < 0.05 versus diluent). Bilaterally applied at ropine led to significant inhibition of ipsilateral and contralateral nasal secretions as well as rhinorrhea scores (p < 0.05 versus placebo ) but had no significant effect on other parameters. Challenge after a tropine premedication led to higher increases in histamine concentrati on than placebo (p < 0.01). These results suggest that parasympathetic ally stimulated fluids did not contain histamine and diluted the hista mine released by mast cells. To support this hypothesis, we challenged the same subjects with methacholine. The concentration of histamine d ecreased and was significantly lower than after challenge with antigen (p < 0.01). The data suggest that: (1) histamine is released locally at the site of antigen challenge, (2) the volume of glandular secretio ns is primarily controlled by parasympathetic stimulation, and (3) the total amount of a mediator recovered in a fixed time interval best re flects the underlying pathophysiologic events.