Stress-induced analgesia. The role of hormones produced by the hypophyseal-adrenocortical system.

Experimental studies on the effects of stress on blood corticosteroid levels and the appearance of analgesia were carried out on rats anesthetized with Nembutai (4 mg/100 g). Stress, consisting of stimulation of the hind footpad with a current at 0.7 mA, produced parallel changes in plasma corticosteroid concentrations and the threshold of a pain response. Functional blockade of the hypophyseal-adrenocortical system, produced by systemic administration of hydrocortisone (15 mg/100 g) or by implantation of dexamethasone (200 micrograms) above the paraventricular nucleus of the hypothalamus, resulted in reductions in stress-induced analgesia. Dosage with naloxone (1 and 10 mg/kg) had no effect on the level of analgesia or corticosteroid concentrations. It is concluded that stress-induced analgesia not mediated by opioids is corticosteroid-dependent.