Acupuncture or electroacupuncture (EA) potentially offers a non-pharmacological approach to reduce high blood pressure (BP). However, approximately 70% of the patients and animal subjects respond to EA, while 30% do not. EA acts, in part, through an opioid mechanism in rostral ventrolateral medulla (rVLM) to inhibit sympathoexcitatory reflexes induced by gastric distention. CCK-8 opposes the action of opioids during analgesia. We therefore hypothesized that CCK-8 in the rVLM antagonizes EA modulation of sympathoexcitatory cardiovascular reflex responses. Male rats anesthetized with ketamine and α-chloralose subjected to repeated gastric distension every 10 min were examined for their responsiveness to EA (2 Hz, 0.5 ms, 1-4 mA) at P5-P6 acupoints overlying median nerve. Repeated gastric distension every 10-min evoked consistent sympathoexcitatory responses. EA at P5-P6 modulated gastric distension induced responses. Microinjection of CCK-8 in the rVLM reversed the EA effect in seven responders. The CCK1 receptor antagonist devazepide microinjected into the rVLM converted six non-responders to responders by lowering the reflex response from 21 ± 2.2 to 10 ± 2.9 mmHg (first vs. second application of EA). The EA modulatory action in rats converted to responders with devazepide was reversed with rVLM microinjection of naloxone (n=6). Microinjection of devazepide in the absence of a second application of EA did not influence the primary pressor reflexes of non-responders. These data suggest that CCK-8 antagonizes EA modulation of sympathoexcitatory cardiovascular responses through an opioid mechanism and that inhibition of CCK-8 can convert animals that initially are unresponsive to EA to become responsive.
- Copyright © 2013, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology