EFFECTS OF AGING ON REGIONAL DIFFERENCES IN THE CONTRACTILE RESPONSESTO ACETYLCHOLINE AND NEUROKININ-A IN RABBIT AIRWAY

1. Experiments were designed to study the effects of ageing on muscari ne and NK2 receptor mechanisms in the three different regions of rabbi t airway. 2. The pD(2) value of acetylcholine changed with age in thre e different regions while that of carbamylcholine, which is resistant to acetylcholinesterase, did not. 3. The pD(2) values of neurokinin A and the activity of protease, a degradative enzyme, changed with age. However, by the pretreatment with phosphoramidon, a protease inhibitor , the regional difference and age related change of the pD(2) value of neurokinin A disappeared. 4. In conclusion, the observations about ag e related changes and regional differences of pD(2) value of acetylcho line and neurokinin A were due to the difference of their degradative enzyme activities.