The continuance time of pressure effect in the rat model of complete Freund’s adjuvant induced arthritis

Abstract

Background: We previously published on the pressure effect using a rheumatoid animal model (Pain Physician in 2013 and 2014). However, we do not know how long the pressure effect lasts after exposure to high pressure. Objective: We evaluated the duration of the pressure effect in a day for a given study period. Study Design: Laboratory animal study. Methods: Following injection of Complete Freund’s Adjuvant (CFA) into one side of the knee joint, 8 rats were assigned to 1.5 atmospheres absolute (ATA) hyperbaric chamber 3 hours per day for one or 2 weeks (1WPG or 2WPG). Pain levels were assessed daily for 2 weeks according to weight bearing force (WBF) of the affected limb. In addition, the levels of gelatinase, MMP-2, and MMP-9 expression in synovial fluids of the knees were analyzed. Results: The reduction of WBF was high at one day after injection and then increased spontaneously up to 2 weeks in 1WPG and 2WPG. The pressure effects lasted for a given day and did not exceed the pressure effects of the next day in all study periods. Improvement of WBF in 2WPG was significantly greater than that of 1WPG during 8~14 days. The gelatinase expression ratio was significantly reduced in 1WPG and 2WPG, and 2WPG showed the lowest gelatinase ratio at 2 weeks. Limitation: Although enough samples were used for the study, more samples will be needed to raise the reliability. Conclusion: The 3 hours of 1.5 ATA pressure effect lasted for more than a day. Longer pressure exposure time appears to yield a greater therapeutic effect in an RA animal model up to a given study period. Continuous application of high pressure might be beneficial for achievement of a better therapeutic effect in clinical application.