AJP - Gastrointestinal and Liver Physiology, Vol 262, Issue 3 510-G516, Copyright © 1992 by American Physiological Society
Evaluation of hepatic venous resistance responses using index of contractility
W. W. Lautt and D. J. Legare
Department of Pharmacology and Therapeutics, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Hepatic vascular responses to 1.25 micrograms.kg-1.min-1 norepinephrine,
infused into the hepatic artery, and 8-Hz nerve stimulation were monitored
in anesthetized cats using a recently introduced index of contractility
(IC). IC was validated in that it did not change passively in response to
passive changes in portal flow or distending blood pressure, whereas the
distensible venous resistance sites showed dramatic changes in resistance.
Resistance is altered by both active contractile responses and passive
distensibility; IC is not altered passively but is affected by changes in
vascular tone. Resistance was a less sensitive index of vasoconstriction
because, although the constriction increased resistance, the subsequent
elevation in portal and intrahepatic pressure counteracted the
constriction; the extent of active neurogenic response using resistance as
the index was grossly underestimated due to venous distensibility. IC
showed that pre- and postsinusoidal constriction occurred to both
norepinephrine and nerves; extensive vascular escape from neurogenic
constriction occurred for the portal vein so that by 5 min almost all the
rise in portal pressure was due to hepatic venous constriction.
