Vessel- and target cell-specific actions of endothelin-1 and endothelin-3 in rat liver

We studied the sinusoidal and extrasinusoidal constrictor response of hepatic microcirculation to endothelin-1 (ET-1) and endothelin-3 (ET-3) and the possible role of Ito cells vs. Kupffer cells or endothelial cells in mediating this response, using isolated rat livers under high-power intravital microscopy. Rats were pretreated by injection of 2.6 x 10(8) fluorescent latex beads (1 micron) intravenously to label Kupffer cells. Three hours later livers were isolated and perfused before and during the infusion of 1 nM ET-1 or ET-3 with or without the endothelin type A (ETA) receptor antagonist BQ-123 or ETB antagonist IRL-1038. Alternatively, the perfused livers were infused with the ETB agonist sarafotoxin 6c (S6c, 1 or 5 nM). Sinusoid diameters were quantitated at the sites of Ito cells (identified by vitamin A fluorescence) or Kupffer cells (phagocytosed fluorescent latex beads) or where neither cell type was found (endothelial cells). ET-1 was found to induce significant sinusoid constriction at the sites of Ito cells (13.21 +/- 0.58 microns control vs. 10.47 +/- 0.48 microns during ET-1 infusion) but not at the sites of Kupffer cells or endothelial cells (13.26 +/- 0.79 vs. 12.92 +/- 0.61 microns and 12.20 +/- 0.71 vs. 11.98 +/- 0.40 microns, respectively), whereas neither ET-3 nor S6c had any effect on sinusoid narrowing, despite a 1.8-fold (ET-3) or 5.6-fold (5 nM S6c) greater increase in total portal resistance compared with ET-1.(ABSTRACT TRUNCATED AT 250 WORDS)