Evaluation of the inflammatory response in two-hit acute lung injury model of rats using ［8F］ FDG microPET

AIM: To investigate whether two-hit acute lung injury (ALI) model is better than one-hit, and to evaluate the inflammatory response in the lungs during these models by using ［8F］FDG microPET. METHODS: Thirty three, adult, male Sprague-Dawley rats weighing 180-210 g were used and divided into 4 groups. Rats in LPS group (n=10) and LPS-HCl group (n=10) were challenged with intraperitoneal administration of LPS at the dose of 5 mg/kg, while rats in NS group (n=3) and HCl group (n=10) received normal saline solution intraperitoneally at the dose of 1 mL/kg, after 16 h, all animals were anesthetized with an intraperitoneal injection of sodium pentobarbital (40 mg/kg) and placed in a 60°inclined position, the femoral artery was cannulated and connected to a pressure transducer to record the arterial pressure on a polygraph recorder, the trachea was surgically exposed. Rats in HCl group and LPS-HCl group received direct intratracheal injection of HCl (pH=1.2) at the dose of 0.5 mL/kg while rats in NS group and LPS group received the same volume of normal saline solution. Blood gas samples (each 0.3 mL) were obtained at 30, 90 and 240 min after the instillation and replaced by the same volume of saline solution, the samples were analyzed using a blood gas analyzer. 240 min after HCl or NS administration, the rats underwent a microPET scanning, then, all the rats were sacrificed and the lungs were obtained for histological analysis. RESULTS: Blood gas analysis showed that rats in LPS-HCl group had higher PaO2 and lower PaCO2 than the other groups. MAP decreased markedly in LPS-HCl group, while MAP in other groups remained stable. The results of microPET showed that the ratio of ROI between the right lung and the muscle tissue of the right arm in LPS-HCl group was 9.00±1.41, and was significantly higher than that in LPS group (4.01±0.60) and HCl group (3.33±0.55). Histological examination showed that the mean lung injury score in LPS-HCl group was 12.70±0.95, while that was 8.40±1.26 in HCl group and 7.00±0.82 in LPS group, and there were significant differences (both P<0.01). CONCLUSION: LPS pretreatment significantly magnifies and prolongs the inflammatory response to the subsequent acid instillation in both lungs. When compared with “one-hit”, “two-hit” is easier to induce the ALI, and ［8F］FDG microPET is a useful tool to evaluate the inflammatory reaction during ALI.