Abstract
1. 1. Nicotine-induced contraction of bronchial preparations isolated from 3, 6, 10, 50 and 100 week old guinea-pigs were studied. 2. 2. Contractile responses to nicotine were inhibited by hexamethonium and a substance P antagonist but not by atropine or tetrodotoxin, suggesting that the nicotine-contraction was mediated through a release of substance P-like material(s). 3. 3. The pD 2 value (potency) of nicotine did not change with age from 3 to 10 weeks but decreased thereafter to 100 weeks, while no age-related change was found in the pD 2 vaule of substance P. The pA 2 value of hexamethonium did not change with age, suggesting that the affinity of drugs to nicotine receptors does not change with age. 4. 4. These results suggest the possibility that age-related change in the pD 2 value of nicotine is due to a change in the amount of nicotine receptors but not to a change in the affinity of nicotine to its receptors.
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