Effect of progesterone on respiratory response to moderate hypoxia and apnea frequency in developing rats

► Progesterone was injected in rats, at 1, 4, 7 and 12 days of age. ► Progesterone decreased baseline apnea frequency in 1-d old rats. ► Progesterone increased peak ventilatory response to hypoxia in 4 and 7 d-old rats. ► Progesterone increased steady state ventilatory response to hypoxia in 1, 4, 7 d-old rats.