Modification of the hepatic hemodynamic response to acute changes in PaCO2 by nitric oxide synthase inhibition in rabbits.
BACKGROUND
Hypercapnia has been reported to modify liver circulation. The vascular regulations implicated in this response remain partly unknown.


METHODS
Using anesthetized and ventilated rabbits, we designed this study to evaluate the hepatic artery and portal vein blood flow velocity adjustments (20 MHz pulsed Doppler) after changes in PaCO2 (by varying the inspiratory fraction of CO2 and to assess the proper role of pH, independent of PaCO2 changes, the role of portal vein CO2, and the effect of nitric oxide synthase inhibition on CO2-induced modifications of hepatic hemodynamics.


RESULTS
Increasing PaCO2 from 30.9 +/- 5 mm Hg to 77 +/- 11 mm Hg increased arterial blood pressure by 20% (P < 0.01) and hepatic artery blood flow velocity by 90% (P < 0.05) and decreased aortic blood flow velocity by 15% and portal vein blood flow velocity by 40% (both P < 0.05). Changes in pH (1 mL of 0.1 N hydrochloric acid infusion) or isolated changes in portal vein CO2 at constant PaCO2 induced by CO2 insufflation in an open abdomen had no effect on hepatic hemodynamics. Pretreatment with a nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine (2.5 mg/kg), blunted the systemic response to hypercapnia, whereas the portal modifications persisted, with a largely attenuated hepatic artery blood flow increase.


CONCLUSIONS
CO2 per se acts on hepatic blood flow by its systemic effect, probably via chemoreflexes. Nitric oxide does not mediate hepatosplanchnic hemodynamic modifications to acute changes in PaCO2 but may play a permissive role by regulating the amplitude of hepatic vascular response.
Losser
Marie-Reine
MR
Department of Anesthesiology and Critical Care Medicine, Lariboisière University Hospital, Paris, France.
Lenfant
François
F
Payen
Didier
D
D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000097:blood*; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006439:Hemodynamics / Q000187:drug effects*; D006499:Hepatic Artery / Q000187:drug effects / Q000503:physiopathology; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia / Q000097:blood / Q000201:enzymology* / Q000503:physiopathology; D008099:Liver / Q000098:blood supply*; D008102:Liver Circulation / Q000187:drug effects*; D008297:Male; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019335:Nitroarginine / Q000494:pharmacology*; D011169:Portal Vein / Q000187:drug effects / Q000503:physiopathology; D011817:Rabbits; D012121:Respiration, Artificial; D014661:Vasoconstriction / Q000187:drug effects
D004791:Enzyme Inhibitors; D002245:Carbon Dioxide; D019335:Nitroarginine; D019001:Nitric Oxide Synthase