Respiratory Regulation by Steroids in Newborn Rats: A Sex-Specific Balance Between Allopregnanolone and Progesterone Receptors

The study investigated the roles of allopregnanolone and progesterone receptors in the respiratory effects of progesterone on newborn rats, with a focus on apnoea frequency. The main finding is that the frequency of apnoea is influenced by a sex-specific balance between allopregnanolone and progesterone receptors. Acute progesterone injection increased apnoea frequency, while finasteride, which inhibits the conversion of progesterone to allopregnanolone, decreased it. Nuclear progesterone receptor agonists reduced apnoea frequency in males, and membrane progesterone receptor agonists did so in both sexes. Chronic progesterone treatment was more effective in reducing apnoea frequency in males than in females. The study used male and female rats aged 10 to 12 days and involved recording respiratory and metabolic parameters. The findings suggest that the effects of progesterone on apnoea are due to its metabolite allopregnanolone and its interaction with GABAA receptors and progesterone receptors, with differences observed between sexes.