Differences in responses of guinea-pig and rabbit airway smooth muscle to adrenaline and adrenergic nerve stimulation

1. The effects of adrenaline and adrenergic nerve stimulation have been studied on tension in preparations of guinea-pig and rabbit airways and related to fluorescence histochemical studies of the distribution of the nerves. 2. Guinea-pig trachea and lung were found to contain inhibitory adrenoceptors. Functional adrenergic nerves were found only in the trachea. 3. In rabbit trachea, bronchus and lung inhibitory adrenoceptors were not demonstrated. Catecholamines caused a contraction in lung strips. Adrenergic nerves were present in the airways although sparse in the fine airways and failed to respond to field stimulation in the three preparations. 4. It is suggested that excitatory responses of rabbit lung strips to catecholamines are mediated via alpha receptors in the fine airways although the possibility that the blood vessels in the tissue caused the response cannot be discounted. 5. An evolutionary basis for the species differences is considered.