[Mechanisms of corticotropin-releasing factor-induced analgesic effect in conscious rats]

The aim of study was to investigate a contribution of hypothalamic-pituitary-adrenocortical (HPA) axis and opioid system in corticotrophin-releasing factor (CRF)-induced analgesic effect in conscious rats during thermal stimulus. The contribution of HPA axis in CRF-induced analgesia was studied with two approaches: 1) pharmacological suppression of HPA axis activity induced by cortisol administration in pharmacological dose one week before experiment; 2) occupation of glucocorticoid receptors by its antagonist RU 38486. The opioid antagonist naltrexone was used to examine the involvement of opioid system in CRF-induced analgesia. Blockade of opioid receptors by its antagonist completely eliminated CRF-induced analgesic effect. Pharmacological suppression of HPA axis resulted in a decrease of CRF-induced analgesic effect, blockade of glucocorticoids receptors by RU-38486 potentiated CRF-induced analgesic effect. The data obtained suggest that CRF-induced analgesic effect is mediated by opioids. The effect ofopioids upon pain sensitivity may be modulated by glucocorticoid hormones.