Allopregnanolone Induces Opioid Inhibition of Hypothalamo-Pituitary-Adrenal Axis Responses to Interleukin-1β in Pregnancy

In this study, researchers investigated the suppression of HPA axis responses to IL-1β in late pregnancy, focusing on the roles of allopregnanolone (AP) and endogenous opioids. Using pregnant and virgin rats, they found that AP and opioids were involved in reducing ACTH secretion in response to IL-1β. Finasteride and naloxone treatments partially restored ACTH responses in pregnant rats, indicating that AP and opioids work together rather than independently. In virgin rats, AP reduced ACTH responses, but naloxone could restore these responses, suggesting that AP induces opioid tone. Additionally, AP increased proenkephalin-A mRNA expression in the nucleus tractus solitarius, which may contribute to the opioid inhibition of HPA responses during pregnancy.