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BACKGROUND/AIMS: When assessing the peritoneal microcirculation with invasive methods, interference with the mechanisms of vaso-regulation may occur. The 133Xe clearance technique renders the possibility, by minimal invasiveness, to estimate the influence of a vasoactive agent on the peritoneal microcirculation. METHODOLOGY: Ten to 15MBq of 133Xe were injected in the abdominal cavity in thirty-eight Wistar-FU (W-FU) rats and 35 Lister-Hooded (LH) rats. A NaI (Tl)-scintillation detector registered activity before and during vasopressin infusion. Gamma camera imaging confirmed the washout from the abdominal cavity. The laser Doppler flowmetry technique was used as a comparison. RESULTS: Vasopressin at 0.07 IU/kg/min IV significantly reduced 133Xe-clearance by 37% (p = 0.029) and 52% (p=0.036) and laser Doppler flowmetry by 69% (p=0.0019) and 44% (p=0.0039) in W-FU and LH rats, respectively. A linear correlation between dose of vasopressin and relative decrease in 133Xe clearance was demonstrated in the W-FU rat model (r2=0.98, p=0.023). The 133Xe clearance from the abdominal cavity in rat using a single-compartment model or the slow compartment in a double-compartment model gave reproducible information. CONCLUSIONS: The usefulness of this mini-invasive technique for sequential measurements before and during intervention will render the 133Xe clearance suitable for assessment of blood flow changes in the abdominal cavity.

Purpose: Intraperitoneal administration of 5-fluorouracil for the treatment of gastrointestinal malignancies results in a greater total drug exposure in the peritoneal fluid than in plasma. Drugs are eliminated from the peritoneal cavity mainly by capillaries leading to the portal venous system and to a lesser extent by lymphatics. The drug itself and the presence of peritoneal carcinomatosis may affect elimination of the drug. The 133Xe-clearance technique allows the influence of a vasoactive agent on the peritoneal blood flow to be estimated with minimal invasiveness. The aim of the present study was to explore whether intraperitoneal 5-FU or peritoneal carcinomatosis affects the peritoneal blood flow and its reactivity to intravenous vasopressin, as measured indirectly with the 133Xe-clearance technique. Methods: The animals used in this study were 63 Wistar-Fu (W-Fu) rats and 67 Lister-Hooded (LH) rats. On day 0, either 5-FU at 25 mg/kg body weight in 25 ml/kg isotonic saline was instilled intraperitoneally, or 1·105 syngeneic tumour cells were inoculated intraperitoneally. On days 1, 2 and 3 in the 5-FU-treated rats, and on days 12–16 in rats inoculated with tumour cells, peritoneal blood flow was analysed with the 133Xeclearance technique, before and during intravenous infusion of vasopressin at 0.07 IU/min/kg body weight. Results: The basal 133Xe-clearance before administration of vasopressin was similar in all groups except in the LH rats treated with 5-FU in which it was significantly lower. Infusion of vasopressin induced a significant decrease in 133Xe-clearance of the same magnitude in controls and in tumour-bearing rats. In the rats given intraperitoneal 5-FU, vasopressin did not reduce the 133Xe-clearance the first day after administration of 5-FU. Conclusions: Intravenous vasopressin at 0.07 IU/ min/kg decreased peritoneal blood flow as measured indirectly with the 133Xe-clearance method. Intraperitoneal 5-FU abrogated the reduction in peritoneal bloo