Methods: Male Japan White rabbits were anesthetized with sevoflurane under mechanical ventilation. Remifentanil was continuously infused at a rate of 0.4µ/kg/min. Naloxone 0.01mg/kg or phentolamine 0.01mg/kg was administered during remifentanil infusion. Observed variables were systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), heart rate (HR), common carotid artery blood flow (CBF), tongue mucosal blood flow (TBF), mandibular bone marrow blood flow (BBF), masseter muscle blood flow (MBF), upper alveolar mucosal blood flow (UBF), and lower alveolar mucosal blood flow (LBF). CBF was continuously monitored using an ultrasonic blood flowmeter (T108; Transonic, lthaca, NY). TBF was continuously monitored using a laser Doppler blood flowmeter (ALF21; Advance, Japan). BBF, MBF, UBF and LBF were measured using a hydrogen clearance tissue blood flowmeter (UHE-100; Unique Medical, Japan). One-way analysis of variance for repeated measurements followed Dunnett test was used.
Results: Remifentanil produced reductions in SBP, HR, CBF, and TBF by about 10% and BBF, MBF, UBF, and LBF by about 25%. In the naloxone group, all variables recovered after naloxone administration. In contrast, in the phentolamine group, blood flow except TBF recovered while hemodynamic variables did not recover after phentolamine administration.
Conclusions: Our findings suggest that tissue blood flow reductions during remifentanil infusion may be at least in part attributable to a-adrenergic mechanisms.