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This study aimed to examine whether livers overexpressing heme oxygenase (HO)-1 could alter the vascular resistance through the vasorelaxing action of carbon monoxide (CO). The relationship among HO-1 expression, CO generation, and the vascular resistance was assessed in perfused rat livers pretreated with hemin, an inducer of HO-1. At 18 h after the hemin treatment, livers displayed marked increases in HO-1 expression in hepatocytes and venous CO flux and a reduction of the basal resistance. The reduction of the resistance in hemin-treated livers was canceled by administration of oxyhemoglobin, a reagent trapping both CO and nitric oxide (NO), but not by methemoglobin, which captures NO but not CO. Liposome-encapsulated oxyhemoglobin, which cannot access the space of Disse, did not cause vasoconstriction. Furthermore, these livers became less sensitive to endothelin-1, a vasoconstrictive peptide, than the untreated controls through mechanisms involving CO. On the other hand, at 12 or 24 h after the treatment when the HO-1 induction was not accompanied by CO overproduction, neither a decrease in the basal resistance nor vascular hyporeactivity to endothelin-1 was observed. These results suggest that CO overproduced in the extrasinusoidal compartment is a determinant of the HO-1-mediated vasorelaxation in the liver.

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Angiodysplasia of the gastrointestinal tract is thought to be one of the most common causes of lower gastrointestinal bleeding in the elderly, and, in the majority of cases, lesions are located in the cecum or ascending colon. The authors report an extremely rare case of appendicular angiodysplasia. A 76-yr-old woman was hospitalized with massive recurrent red anal bleeding. Selective superior mesenteric arteriography revealed an extravasation of contrast material from the appendicular artery, and this finding proved to be bleeding from an angiodysplasia of the appendix. An appendectomy was performed, and anal bleeding did not recur postoperatively. A review of the literature revealed this to be an extremely rare case of angiodysplasia.