Further evidence for abnormal hindquarter tone in spontaneously hypertensive rats

In spontaneously hypertensive rats (SHR) and normotensive control rats (NCR), hindquarter flow was observed in the conscious state with an electromagnetic flow probe chronically implanted around the terminal aorta. Arterial pressure was recorded with an indwelling catheter in the common carotid. When arginine vasopressin was infused intravenously at a rate of 12.5 ng/(kg.min), the increase in hindquarter resistance, calculated as arterial pressure divided by hindquarter flow, was significantly (p less than 0.005) augmented after ganglionic blockade with hexamethonium in SHR but not in NCR. This is explicable by assuming a tonic sympathetic vasoconstrictor activity in the hindquarters of SHR, reflexive inhibition of which partially offsets vasoconstrictor effect of infused vasopressin.