Abstract
We examined the correlation between airway hyperreactivity and the density of muscarinic acetylcholine receptor (mACh-R), and reported that the density of mACh-R in OA-sensitized guinea pig was higher than that in a control group. We also examined the characteristics of the M1, M2 and M3 receptors in guinea pig pulmonary tissue, and the following results were obtained.
1) For the M1 and M2 receptors, no difference was observed between the density and affinity of OA-sensitized lungs and those of the control lungs.
2) The density of M3 receptors in the lung tissue of OA-sensitized guinea pigs washigher than that in the control group. No difference was observed between the affinity of M3 receptors in the OA-sensitized lungs and that in the control lungs.
3) Pilocarpine, which is an M2 receptor agonist, increased the density of M3 receptors in the lung tissue of guinea pigs, and the rate of the increase in the density of M3 receptors in OA-sensitized guinea pigs was less than that in the control group. On the other hand, methoctramine, which is an M2 receptor antagonist, decreased the density of M3 receptors in the lung tissue of guinea pigs, and the rate of this decrease was as same as that in the control group.
These results suggest that the increase in M3 receptors in the lung tissue of OA-sensitized guinea pigs is related to airway hyperreactivity and that there is a dysfunction of M2 receptors in OA-sensitized guinea pigs.
