Responses to hypotension in conscious rats with chronic portal venous hypertension

Heart rate, mean arterial pressure, and vascular conductance response to intravenous nitroprusside were compared in conscious, unrestrained portal vein-stenosed and sham-operated rats chronically instrumented for pulsed Doppler flowmetry. Ten to twelve days after portal vein stenosis, portal venous pressures were elevated and resting heart rates were greater. Portal vein-stenosed animals' depressor responses to nitroprusside were similar to those of sham-operated animals, despite a 41% reduction in their tachycardic response to arterial hypotension. Skeletal muscle vascular bed reflex responses to nitroprusside-induced hypotension were significantly attenuated in the portal vein-stenosed group, whereas their renal artery and superior mesenteric artery responses resembled that of the sham-operated group. After ganglionic blockade, tachycardic responses to hypotension were abolished, but portal vein-stenosed rats' heart rates remained greater than sham-operated rats. Comparisons of arterial pressure changes, renal artery, abdominal aorta, and superior mesenteric artery vascular conductance changes after ganglionic blockade revealed no differences in neurogenic vascular tone between groups. Ganglionic blockade enhanced nitroprusside depressor responses and increased vascular conductance responses to nitroprusside in both treatment groups while abolishing the between group difference in the skeletal muscle baroreflex response. These findings indicate that chronic prehepatic portal vein stenosis with portal venous hypertension results in reduced reflex tachycardic and skeletal muscle baroreflex responses to nitroprusside-induced hypotension.