[Changes in the circulation and blood catecholamines following electrical stimulation to the infraorbital nerve in rabbits which had received a long-term administration of imipramine].

The purpose of the present study was to observe how circulation would be affected with imipramine. An experimental model of rabbits which had received a long-term administration of imipramine was prepared, and electrical stimuli were applied to the infraorbital nerve to determine: i) the circulatory responses (the mean femoral arterial blood pressure, the regional cortical blood flow in the marginal gyrus measured by a hydrogen clearance method and the carotid blood flow measured by using an electromagnetic blood flow meter): and ii) the catecholamine levels in the femoral arterial blood and in the brain tissues, and the imipramine level in the left-ventricular blood measured by high performance liquid chromatography. After norepinephrine (4 micrograms/kg) was infused into the femoral vein, the electrical stimuli were applied to the infraorbital nerve to determine circulatory responses. The rabbits were initially anesthetized with a mixture of nitrous oxide, oxygen and halothane during the operation for the placement of the measuring device. During measurement the animal were lightly anesthetized with the same gas under spontaneous respiration through a tracheal cannula. The data obtained from the group of rabbits to which imipramine had been administered were compared with those obtained from the control group. The results of the present study are as follow: 1) The cerebral blood flow in both groups increased significantly (p less than 0.05, p less than 0.01) following the application of the electrical stimuli to the infraorbital nerve. When the same stimuli applied after norepinephrine had been infused into the femoral vein the cerebral blood flow was further increased (p less than 0.01). 2) The natural norepinephrine level in the femoral arterial blood increased significantly (p less than 0.001) in the imipramine group following the application of the electrical stimuli. 3) Although the natural norepinephrine level in the femoral arterial blood increased following the application of the electrical stimuli, the mean femoral arterial blood pressure and the carotid blood flow decreased significantly (p less than 0.05) in the imipramine group. It is considered that the decreases of the blood pressure and the cardiac blood flow were probably due to the reduction of the cardiac output.