Supraspinal origin of abnormal hindquarter vasoconstrictor tone in spontaneously hypertensive rats

The object of this study was to determine whether the abnormal hindquarter tone in spontaneously hypertensive rats (SHR) is of spinal origin or not. SHR were implanted with a catheter in the left common carotid and an electromagnetic flow probe around the terminal aorta. About three days after implantation, the spinal cord was transected at Th 1 under ether anesthesia. One hour later, when the rat restored consciousness and the arterial pressure recovered partially to a new plateau level which was significantly higher than that in similarly treated normal rats, ganglionic blockade with hexamethonium did not significantly decrease hindquarter (terminal aortic) resistance, calculated as arterial pressure divided by hindquarter flow. It was concluded that there was no appreciable sympathetic vasoconstrictor tone in the hindquarters of SHR after spinal transection and that the origin of the abnormal tone was at the supraspinal level.