The nasal
antigen challenge model has proved useful in assessing the roles of inflammatory mediators in the clinical allergic response. Studies using this model have revealed that the acute allergic response is associated with increased concentrations of
histamine,
prostaglandin D2 (
PGD2),
leukotrienes,
tryptase, and
kinins, and with increased
TAME-esterase activity. The effects of
antihistamines on the clinical response and inhibition of mediator release have also been examined with this model.
Premedication with
terfenadine caused a marked reduction in
sneezing as well as decreased histamine release,
kinin levels, and
TAME-esterase activity. Levels of
PGD2 also decreased, although not significantly. Release of
leukotriene C4 (
LTC4) was not affected by this agent.
Terfenadine also reduced vascular permeability as reflected in decreased
albumin levels. In this model,
cetirizine reduced
sneezing,
TAME-esterase activity, and
albumin levels, whereas histamine release and
PGD2 levels remained unaffected. Pretreatment with
cetirizine resulted in significantly reduced levels of
LTC4.
Loratadine markedly, but not significantly, inhibited the
sneezing response and reduced release of
histamine,
PGD2, and
LTC4.
Albumin and
kinin levels were significantly diminished. The clinical significance of the inhibitory effects of
antihistamines on mediator release has yet to be determined.