Adrenergic and cholinergic responses of the tracheal smooth muscle is enhanced during estrus phase in rat

Aim: The aim of this study was to evaluate influences of hormonal changes during rat estrous cycle on airway responsiveness to bronchoconstrictor and bronchodilator agents. Materials and methods: The study was performed in 5 groups of rat tracheal smooth muscle obtained during proestrus,estrus, metestrus, and diestrus phases of the estrous cycle, as well as the ovariectomized group (n:8/group). Cumulative acetylcholine contractions ranging from 10-8to 10-3M bath doses and the cumulative isoproterenol relaxations ranging from 10-8to 10-3M precontracted with 10-5M of acetylcholine were recorded on isolated tracheas placed in a computerized tissue bath system. Results: Acetylcholine-induced contractions ranging from 10-5to 10-3M were significantly enhanced dose-dependently in tracheal smooth muscle from estrus rats compared to those from metestrus and ovariectomized rats. The relaxation induced by isoproterenol (10-8-10-3M) also significantly increased in tracheal smooth muscle precontracted with acetylcholine (10-5 M) taken from estrus rats. However, acetylcholine-induced contractility increase in tracheal smooth muscle was much more prominent than isoproterenol-induced relaxations in tracheal smooth muscle from estrus rats.Conclusion: These findings indicated that changes in estrogen and/or progesterone levels during rat estrous cycle might affect acetylcholine and isoproterenol sensitivity of the tracheal smooth muscle.