Age-related changes in muscarinic cholinoceptor function in guinea-pig and rat airways

The influence of age on muscarinic cholinoceptor-mediated contraction and inositol phosphate accumulation was examined in rat and guinea-pig isolated tracheal tissue. Significant age-related changes in the sensitivity of guinea-pig tracheal tissue to acetylcholine, but not carbachol, were observed in the early maturation phase of growth with a 3.3-fold increase in potency between birth and 2 weeks of age followed by a 3.2-fold fall in potency between 2 and 12 weeks of age. Further ageing did not significantly change the potency of acetylcholine or carbachol. Whilst acetylcholinesterase inhibition caused a significant increase in acetylcholine potency, this was independent of animal age. In rat isolated tracheal tissue, contractile responses to both acetylcholine and carbachol remained unchanged with respect to animal age. Significant age-related decreases in inositol phosphate accumulation were observed in response to carbachol in the guinea-pig and rat and to acetylcholine in guinea-pig but not rat isolated tracheal tissue. This study has demonstrated significant age-related changes in the responsiveness of isolated tracheal tissue to carbachol and acetylcholine which were also species-specific.