Chronic drug treatments induce changes in the sensitivity of presynaptic autoreceptors but not of presynaptic heteroreceptors

Guinea-pigs were sensitized to ovalbumin by an intraperitoneal injection, followed 3 weeks later by daily aerosol exposure for 4 weeks. Noradrenaline-induced contractons of peripheral lung strips from sensitized and unsensitized guinea-pigs were compared. There were no differences in sensitized or unsensitized strips with respect to maximal tension generated, concentration of noradrenaline for threshold or maximal responses or EC₅₀. These results suggest that any changes in the population of α-adrenoceptors consequent upon immunological sensitization did not influence contractile responses to noradrenaline.