DAMGO Stimulates the Hypothalamo-Pituitary-Adrenal Axis

DAMGO, a highly selective mu opioid agonist, is capable of stimulating the hypothalamo-pituitary-adrenal (HPA) axis to pro-duce a dose-related elevation in plasma corticosterone (CS). The purpose of this study was to confirm that this action was mu receptor selective and to determine which of the mu receptors was involved using naloxonazine, a mu-i receptor-selective an-tagonist. Experiments were done in male rats with chronic i.v. catheters and i.c.v. cannula guides. This enabled the withdrawal of serial blood samples in conscious unrestrained animals that were isolated in sound-attenuated one-way vision boxes. DAMGO, 8 and 1 6 g administered i.c.v. caused significant and prolonged elevation of plasma CS. $-funaltrexamine (-FNA) in progressively increasing doses (i.c.v.), antagonized the effect of DAMGO. The hormone response to DAMGO was unaffected b