1 Seven atopic subjects received two injections of antigen and one of saline intradermally in the back on each of 4 separate days. They were pretreated with four different drug combinations: (a) adrenaline 0.3 mg subcutaneously over the deltoid muscle (b) subcutaneous adrenaline preceded by 5 mg of the specific ,32-adrenoceptor antagonist ICI 118,551 orally (c) 8 mg of salbutamol orally (d) placebo. Tablets were given 2 h before and subcutaneous injections 15 min before the intradermal injections of saline and antigen. 2 The median flare response to intradermal low dose antigen and high dose antigen after pretreatment with adrenaline was 4% and 49% of the response seen following pretreatment with placebo (P < 0.001). When adrenaline was preceded by ICI-118,551, the corresponding median flare responses were 2% and 44% (P < 0.001) of the placebo response. The flare response after pretreatment with salbutamol was not significantly different from placebo.3 Adrenaline suppressed the median weal response to the higher dose of antigen to 52% of the response after pretreatment with placebo (P < 0.05). This suppression by adrenaline was blocked by pretreatment with ICI 118,551. The median weal response after the highest dose of antigen was suppressed by salbutamol to 66% of the response seen after placebo, although this was not significant even when a further three subjects were studied with either salbutamol or placebo. 4 These results confirm that a small dose of systemic adrenaline attenuates the weal and flare response to intradermal antigen. This suppression of the weal response is blocked by a P2-adrenoceptor antagonist although it is only partially mimicked by high dose oral salbutamol. The suppression of the flare response may involve a-adrenoceptor stimulation.

On three separate occasions 12 atopic subjects were injected intradermally with two doses of antigen and one of saline as control. Pretreatment with terfenadine 60 mg orally significantly inhibited the flare response to both the lower dose of antigen and to saline (P less than 0.05). Ingestion of enalapril 5 mg orally 3 h before increased the flare response to both doses of antigen. Neither enalapril nor terfenadine affected the weal response when compared with placebo. Both endogenous histamine and bradykinin appear to be released during the intradermal flare response but are not important in the weal reaction to antigen.

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