An endothelin A receptor antagonist induces dilatation of sinusoidal endothelial fenestrae: implications for endothelin-1 in hepatic microcirculation.
BACKGROUND
Sinusoidal endothelial fenestrae (SEF) regulate the sinusoidal circulation by altering their diameter and number. This study documented the effects of endothelin (ET) receptor antagonists on SEF and hepatic microcirculation.


METHODS
The portal pressure and hepatic tissue blood flow were measured with a hydromanometer and a laser Doppler blood flow meter, respectively. BQ-123 (ET(A) receptor antagonist) or BQ-788 (ET(B) receptor antagonist) was continuously infused into normal rats at the rate of 10 nmol/min for 10 min. The sinusoids were observed at 60 min after the infusion by scanning electron microscopy. The localization of ET-1 and ET(A) and ET(B) receptors was examined by the indirect immunoperoxidase method.


RESULTS
When BQ-123 was infused, the portal pressure gradually decreased with time, and it showed a significant reduction compared with the control groups. On the other hand, a decrease in portal pressure was not evident in the BQ-788-infused groups. Hepatic tissue blood flow was maintained at the value prior to the infusion in both groups. BQ-123 also caused a marked dilatation of the SEF. The diameters of the SEF after BQ-123 infusion were almost three times those of normal SEF. ET-1 was evenly present along the sinusoidal walls, and the reaction products of the ET(A) receptors were recognized along the portal vein and in the sinusoidal cells, that is, the hepatic stellate cells and endothelial cells.


CONCLUSIONS
Action of ET-1 via the ET(A) receptors may regulate the size of SEF in addition to hepatic microcirculation.
Watanabe
Norihito
N
Division of Gastroenterology, Department of Internal Medicine, Tokai University School of Medicine, Bohseidai, Isehara, 259-1193, Japan.
Takashimizu
Shinji
S
Nishizaki
Yasuhiro
Y
Kojima
Seiichiro
S
Kagawa
Tatehiro
T
Matsuzaki
Shohei
S
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000648:ultrastructure; D006975:Hypertension, Portal / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D007150:Immunohistochemistry; D008099:Liver / Q000098:blood supply*; D008102:Liver Circulation / Q000187:drug effects*; D008297:Male; D008833:Microcirculation / Q000187:drug effects; D017348:Microscopy, Electron, Scanning Transmission; D010456:Peptides, Cyclic / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D000959:Antihypertensive Agents; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D010456:Peptides, Cyclic; C072247:cyclo(Trp-Asp-Pro-Val-Leu)