Failure of hydrocortisone and 2% saline treatment to abolish morphine and stress-induced analgesia in rats.

It has been demonstrated that analgesia induced by physiological stress (1. 6) and electro-acupuncture (8) may be mediated through an endogenous opioid mechanism. It is also known that acute stressful stimuli cause a concomitant release of ,8-endorphin and adrenocorticotropin (ACTH) from the pituitary gland (4). Both these are peptides derived from a common precursor molecule (7) and the release of ,8-endorphin is also considered to be regulated by the same feedback system which is concerned with ACTH release (9). With these reports in view we have examined the effect of repeated injections of hydrocortisone (a treatment which inhibits ACTH-release) and of 2% saline-treatment. reported to deplete pituitary p-endorphin by 50% (3) on morphine and heat stress-induced analgesia in rats. It was hoped that the study would indicate the relevance of endogenous opioid release in stress-induced analgesia.