Positive feedback action of pituitary beta-endorphin on acupuncture analgesia afferent pathway.

Potentials in the final sector of the afferent pathway from the acupuncture point (AP) were enhanced by intraperitoneal 0.5 mg/kg morphine without changing the threshold of AP stimulation and greatly decreased by hypophysectomy. The decreased potentials were restored to the control level by morphine (0.5 mg/kg, IP). Potentials evoked in the final sector of the afferent pathway from the nonacupuncture point (NAP) by NAP stimulation after lesion of the analgesia inhibitory system were greatly enhanced by corticotropin (ACTH) (0.25 mg/kg, IP) and greatly decreased by hypophysectomy. Diminished potentials were restored to the control level by ACTH (0.25 mg/kg, IP). Both morphine (0.5 mg/kg, IP) and ACTH (0.25 mg/kg, IP) produced analgesia, but morphine did not affect acupuncture analgesia (AA) and ACTH did not affect nonacupuncture point stimulation-produced analgesia (NAA). All analgesia, that due to 0.5 mg/kg morphine or 0.25 mg/kg ACTH, AA, and NAA were abolished by hypophysectomy. The abolished AA and NAA were restored by 0.5 mg/kg morphine and 0.25 mg/kg ACTH, respectively. Hence, beta-E and ACTH liberated from the pituitary gland by stimulation of an AP and NAP may act as positive feedback on the AA and NAA afferent pathways, respectively.