Electroacupuncture-induced analgesia in sheep: measurement of cutaneous pain thresholds and plasma concentrations of prolactin and beta-endorphin immunoreactivity.

Eleven male and 15 female sheep were subjected to electroacupuncture (EA) treatment, using 2 needle loci described in the Chinese veterinary literature as Yao Pang (lumbar region) and San Yang Lu (1 thoracic limb). Noninjurious cutaneous stimuli were applied, using a calibrated pin-prick probe, a clamp, and a contact heat (75 to 95 C) probe. Cutaneous pain thresholds (PT) were quantified in 7 body areas during control (no acupuncture needles and no electrostimulation) and EA experiments, before and after IV injection of naloxone. Using each animal as its own control, each EA experiment was classified as inducing either good or poor anagelsia on the basis of whole-body PT values. Plasma concentrations of immunoreactive beta-endorphin (beta E) and prolactin were quantified in sequential plasma samples collected at 9-minute intervals throughout all experiments. Electroacupuncture at each locus increased (P less than 0.01) PT (ie, caused cutaneous analgesia) in 6 of 7 body areas, and increased (P less than 0.05) plasma concentrations of immunoreactive beta E and prolactin. In EA experiments in which good analgesia was induced, plasma beta E was increased more (P less than 0.05) than in EA experiments in which poor analgesia was induced. This difference was more evident for the Yao Pang locus. Generally, plasma prolactin concentrations were increased more with good analgesia than with poor analgesia for the Yao Pang locus. Electroacupuncture stimulation of the San Yang Lu locus was associated with higher plasma beta E concentrations than that associated with the Yao Pang locus. Increases in plasma prolactin concentrations were comparable between loci.(ABSTRACT TRUNCATED AT 250 WORDS)