Intrathecal phentolamine increases blood flow and skin temperature in the hind limbs of dogs.

Spinal anesthesia with local anesthetics increases blood flow and skin temperature in the lower extremities. Although the effect of α2 adrenoceptor agonists on the spinal cord has been confirmed, there has been no such report of the effects of α-adrenoceptor antagonists. We studied the effects of intrathecal administration of phentolamine on the blood flow in the femoral artery and skin temperature in the hind limbs of seven dogs. One ml of 3% lidocaine (L group) or 1 ml of 0.1% phentolamine (P group) was injected into the intrathecal space. Blood flow significantly increased at 3 min in both groups, and no significant difference was observed between the groups at any phase. Pad skin temperature in the hind limbs increased significantly at 5 min in the L group and at 3 min in the P group (P<0.05). The only significant difference was observed at 30 min. High pad skin temperature continued for 60 min in the L group and for 90 min in the P group. With phentolamine i.v. (1 mg), there were no changes in blood flow in the femoral artery or pad skin temperature; there was only a decrease in blood pressure. In conclusion, the intrathecal α-adrenoceptor antagonist, phentolamine, increases blood flow in the femoral artery and pad skin temperature in hind limbs in dogs similar to lidocaine.