Role of nitric oxide in extracellular nucleotide-induced contractile status of assorted vessels including parts of the portal vasculature.
OBJECTIVE
The resistance of portal vein and hepatic artery plays an important role in the regulation of the circulatory status in the liver, but the regulatory mechanisms for these hepatic vessels have still to be elucidated. The aim of this study was to discover the tonus regulation of the hepatic vasculature.


METHODS
The effects of adenosine, adenosine 5'-monophosphate, adenosine 5'-diphosphate, adenosine 5'-triphosphate and uridine triphosphate on the force generation of the portal vein, superior mesenteric artery, inferior caval vein and aorta of the rat were studied in vitro. Each vessel was removed and cut into 5-mm ring strips. The strips were fixed vertically between triangle hooks and incubated in organ baths containing Krebs-Henseleit solution. The change in vascular tension was continuously monitored by a force-displacement transducer and recorded isometrically with a polygraph.


RESULTS
Adenosine 5'-diphosphate and adenosine 5'-triphosphate induced relaxation of superior mesenteric artery and aorta precontracted with prostaglandin F2alpha dose-dependently. The effects of adenosine 5'-diphosphate and adenosine 5'-triphosphate were attenuated in the presence of N(G)-nitro-L-arginine, indicating nitric oxide dependency. In contrast, all these nucleotides dose-dependently induced contraction of the portal vein obtained from the hepatic hilus. N(G)-nitro-L-arginine decreased the EC50 values for these metabolites. Interestingly, all the nucleotides failed to induce contraction of the inferior caval vein and the portal vein distal to the hepatic hilus.


CONCLUSIONS
These results suggest that some purinoceptor-dependent pathway regulates contraction of the portal vein close to the hepatic hilus and elicits, in contrast, the relaxation of superior mesenteric artery and aorta. Nitric oxide may participate in the tonus regulation of hepatic vasculature.
Minamiyama
Y
Y
1st Department of Biochemistry, Osaka City University Medical School, Osaka, Japan.
Takemura
S
S
Kawada
N
N
Inoue
M
M
D000818:Animals; D006499:Hepatic Artery / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects; D008833:Microcirculation / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects; D009569:Nitric Oxide / Q000502:physiology*; D019335:Nitroarginine / Q000494:pharmacology; D009711:Nucleotides / Q000494:pharmacology*; D011169:Portal Vein / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014682:Vena Cava, Inferior / Q000187:drug effects*
D009711:Nucleotides; D014662:Vasoconstrictor Agents; D019335:Nitroarginine; D009569:Nitric Oxide