Effect of Elevated Intra-Abdominal Pressure and Hyperoxia on Portal Vein Blood Flow, Hepatocyte Proliferation and Apoptosis in a Rat Model

Abstract

Indications for a laparoscopic approach for the management of biliary atresia in children are not clearly defined. We have recently shown that persistent intra-abdominal pressure (IAP) significantly decreased portal vein (PV) flow. Ventilation with a high concentration of oxygen after abdomen deflation raises concerns of increased oxidative stress but has also been shown to exert beneficial effects on splanchnic ischemia/reperfusion. The purpose of the present study was to evaluate the effects of IAP and hyperoxia on liver histology, hepatocyte proliferation and apoptosis in a rat model of abdominal compartment syndrome (ACS). Male Sprague-Dawley rats were anesthetized with intraperitoneal ketamine and xylasine. After a midline laparotomy, the PV was isolated. Ultrasonic blood flow probes were placed on the vessel for continuous measurement of regional blood flow. Mean arterial blood pressure (MABP) was continuously measured. Two large-caliber percutaneous peripheral intravenous catheters were introduced into the peritoneal cavity for inflation of air and measurement of IAP. Rats were divided into three experimental groups: 1) Sham rats were subjected to IAP of 0 mmHg; 2) ACS rats were subjected to IAP of 6 mmHg for 2 hours and were ventilated with air; and 3) ACS-O (2) rats were subjected to IAP of 6 mmHg for 2 hours and were ventilated with 100 % O (2) during the operation and ventilation was continued for 6 hours after operation. Liver structural changes, hepatocyte proliferation (using BrdU assay) and apoptosis (using Tunel assay) were determined 24 hours following operation. IAP at 6 mmHg caused a twofold decrease in PV flow compared to sham animals. Hyperoxia resulted in a less significant decrease in PV flow compared to air-ventilated animals. Despite a significant decrease in PV blood flow, 24 hours after abdominal deflation only a few animals demonstrated histological signs of liver damage. The small histological changes were accompanied by increased hepatocyte apoptosis and enhanced hepatocyte proliferation in 25 % of animals, suggesting a liver repair response. Despite a significant decrease in PV blood flow, persistent IAP for 2 hours results in few changes in liver histology, and stimulates hepatocyte proliferation and apoptosis in only a few animals, supporting the presence of a recovering mechanism. Treatment with hyperoxia did not significantly change hepatocyte proliferation and apoptosis.