Effect of ageing on alpha 1A-adrenoceptor mechanisms in rabbit isolated bronchial preparations

Effect of aging on alpha 1A-adrenoceptor mechanisms in rabbit bronchial preparations was studied. The potency (pD2 value) of norepinephrine increased with age from 5 to 13 weeks and thereafter did not alter with age from 13 to 180 weeks. The affinity of norepinephrine (pKA value) and of a selective alpha 1A-adrenoceptor blocker, 5-methylurapidil (pA2 value) did not alter with age. Efficacy of norepinephrine was proportional to receptor reserve (pD2-pKA). These results suggest that age-related changes in alpha 1A-adrenoceptor mechanisms are due to changes in receptor reserve or total concentration of receptors, but not to changes in affinity of drugs to alpha 1A-adrenoceptors and in contraction mechanisms.