The role of opioid receptors and vagus and sympathetic nerves in remifentanil-induced cardiovascular depression in rabbits / 中华麻醉学杂志

ABSTRACT

Objective To investigate the role of opioid receptors and vagus and sympathetic nerves in the remifentanil-induced cardiovascular depression in rabbits. Methods Forty 2-6 months old New Zealand white rebbits of both sexes weighing 1.5-2.5 kg were randomly divided into 5 groups (n = 8 each) group Ⅰ remifentanil (group R); group Ⅱ naloxone + remifentanil (group N+ R); group Ⅲ vagus nerve cut-off +remifentanil (group V+ R); group Ⅳ epidural block + remifentanil (group S+ R) and group V vagus nerve cutoff + epidural block + remifentanil (group V + S + R). The animals were anesthetized, tracheostomized and mechanically ventilated. PaCO2 was maintained at 35-45 mm Hg. Vecuronium 0.3 mg/kg was given iv every 40 min to keep muscle relaxed. Right carotid artery was cannulated for continuous MAP monitoring. ECG was continuously monitored. A bolus of remifentanil 5.0 μg/kg was administered iv in all 5 groups. In group N + R naloxone 40μg was given iv about 2 min before remifentanil. In group V + R bilateral vagus nerves were cut off through neck incision. After HR and MAP had stabilized for 30 min, remifentanil was given iv. In group S + R epidural block was performed at L6.7 interspace with 2% lidocaine to block cardiac sympathetic nerves. When HR and MAP decreased by 20% of the baseline values and stabilized for 30 min remifentanil was given iv. In group V + S + R bilateral vagus nerves were cut off first. Then epidural block was performed before remifentanil administration. MAP and HR were recorded at 1 min before iv remifentanil administration (T0 ), at 30 s (T1), 1,2, 3, 4, 5, 10, 15 and 20 min (T2-9 ) after remifentanil administration. Results Intravenous remifentanil 5.0 μg/kg significantly decreased HR at T1 and MAP at T1-7 as compared with those at T0 in group R. Pretreatmentwith naloxone 40 μg prevented remifentanil-induced decrease in MAP but did not affect remifentanil-induced decrease in HR in group N + R. Vagus nerve cut-off and sympathetic block induced by epidural anesthesia performed before iv remifentanil did not affect remifentanil-induced cardiac depression in group V + R, S + R and V + S + R. Conclusion Opioid receptors and vagus and sympathetic nerves are not related to remifentanil-induced decrease in HR. Remifentanil induces decrease in MAP by activating opioid receptors.