Prolonged Foot-Shock Induced Analgesia: Glucocorticoids and Non-Pituitary Opioids Are Involved

In rats, the analgesic response induced by prolonged intermittent foot-shock is abolished by naloxone or adrenalectomy, and is restored in adrenalectomized animals by the administration of dexamethasone or corticosterone, but not deoxycorticosterone. Levels of immunoreactive beta-endorphin in the anterior pituitary are significantly elevated by adrenalectomy alone, and further by dexamethasone and corticosterone; in contrast, immunoreactive beta-endorphin levels in the neuro-intermediate lobe are raised by deoxycorticosterone. These findings suggest that analgesic responses produced by prolonged intermittent foot-shock involve both the pituitary-adrenal axis and endogenous, non-pituitary opioids.