針鎮痛発現における下垂体の関与について

Abstract

In order to investigate the involvement of pituitary beta-endorphin in electroacupuncture analgesia (EAA), the effects of hypophysectomy, dexamethasone (Dex) and adrenalectomy on the analgesia and the increase in plasma corticosterone (Cort) and ACTH levels produced by electroacupuncture (EA) were studied in male SD rats. In saline-treated and Dex-treated rats, plasma Cort levels were correlated with plasma ACTH levels. In non-treated rats, the time course of EA-induced increase in pain threshold was similar to that of EA-induced elevation of plasma Cort levels. In the hypophysectomized rats, EAA was significantly reduced and the EA-induced increase in plasma Cort was also abolished. Single administration of a large dose of Dex tended to reduce EAA and significantly reduced the EA-induced increase in plasma Cort and ACTH. Further suppression of pituitary functions by 4 days-treatment with Dex resulted in further reduction of EAA and the EA-induced increase in plasma Cort and ACTH. On the other hand, hind-paw pressure test without EA produced an increase in plasma Cort and ACTH to the same extent as that produced by EA and produced no analgesia. In the adrenalectomized rats, EAA was reduced, and the plasma ACTH level, which was sixteen times higher than that of nonoperated rats, was further elevated 2-fold higher by EA. No correlation between plasma ACTH levels and the increase in pain thresholds was observed in individual rats of the saline-treated and Dex-treated groups. Control pain thresholds were not influenced by hypophysectomy, Dex or adrenalectomy. These results suggest that pituitary beta-endorphin may not be mainly involved in EAA.