AJP - Gastrointestinal and Liver Physiology, Vol 257, Issue 5 773-G781, Copyright © 1989 by American Physiological Society
Pressor responses in conscious rats with chronic portal venous hypertension
H. D. Battarbee, G. E. Farrar and R. P. Spears
Department of Physiology and Biophysics, Louisiana State University Medical Center, School of Medicine, Shreveport 71130.
Heart rate, mean arterial pressure (MAP), and vascular conductance
responses to graded phenylephrine (PE) infusions were compared in
conscious, unrestrained portal vein-stenosed (PS), and sham-operated (SO)
rats chronically instrumented for pulsed Doppler flowmetry. Ten days after
stenosis, MAP was lower in PS than in SO, and PS heart rates were higher.
Pressor sensitivity to PE was attenuated 70%, and bradycardic responses to
increases in MAP were 47% greater in PS. Abdominal aorta vascular bed
conductance sensitivity was reduced 84%, and renal artery sensitivity was
reduced 29% in PS compared with SO, whereas the superior mesenteric artery
conductance response was unaffected by portal vein stenosis. After
ganglionic blockade, the heart rate of PS remained greater than that of SO,
and comparisons of renal artery, abdominal aorta, and superior mesenteric
artery vascular conductances revealed no significant differences in
neurogenic vascular tone. Differences between PS and SO pressor responses
were abolished by ganglionic blockade, as were differences in vascular bed
conductance responses. These findings suggest that a greater bradycardic
response and greater baroreflex-mediated withdrawal of sympathetic tone
from skeletal muscle and renal vascular beds were responsible for the
decreased pressor sensitivity observed in PS animals.
