Cutaneous analgesic, respiratory and cardiovascular effects, and beta-endorphin concentration in CSF and plasma of horses after electro-acupuncture

Abstract

We tested the hypothesis that electro-acupuncture (EAP) can activate the horse's pain modulation system (pituitary or brain stem) to release beta-endorphin in spinal fluid and plasma which provides pain relief in horses. Eight adult healthy mares (510 ± 40 kg) were used in a randomized-crossover design study of 2 hours of EAP (test) and needle placement without electrical stimulation (sham-controls) with at least 3 weeks between experiments. Catheters were aseptically placed in the lumbar subarachnoid space, left carotid artery, and jugular vein of mares, using local anesthesia (2% lidocaine). Cerebrospinal fluid (3 mL) and venous blood (10 mL) were collected for radioimmunoassay of beta-endorphin (Tejwani et al., Life Sci. 1985). Arterial blood pressure, blood pH, PO2, PCO2, PCV, and TS concentrations were determined. Hwato acupuncture needles (28 gauge, 12.5 cm) were inserted at BL 18, 23, 25, and 28 on both sides of the spinal column of mares and were stimulated by an EAP stimulator (ITO IC 4107) using 15 and 30 Hz alternating frequencies, 4 V, 1 mA, and 0.1 ms biphasic square pulses in the test mares. Nociceptive skin pain threshold was measured by skin twitch reflex latency (STRL) and avoidance to radiant heat (48.5 °C cut-off) at the paralumbar fossa. Numerical scores of STRL, sedation, ataxia, respiratory and cardiovascular function, and beta-endorphin concentration in CSF and venous plasma were determined before (time 0), and 30, 60, 90, and 120 minutes after beginning and cessation of EAP and sham-controls. Two-way anova with repeated measures and Dunnett's post test were used. EAP significantly (p < 0.001) increased STRL [12.4 ± 2.1 seconds (mean ± SD) at baseline; 17.3 ± 2.2 seconds at 2 hours after EAP] and concentration of CSF beta-endorphin [17.5 ± 3.9 pg mL−1 (mean ± SD) at baseline; 26.1 ± 6.2 pg mL−1 at 2 hours after EAP], and minimally affected behavior and respiratory and cardiovascular systems of adult mares during and after the 2 hour-testing period.