Oxazolone as a Model to Induce Edema in the Lower Limb of Rats

Purpose. Peripheral edema is a condition characterized by the accumulation of excess interstitial fluid in distal tissues and commonly manifests in the arms or legs. Untreated complex peripheral edema can progress into chronic lymphedema as impaired fluid drainage and chronic inflammation cause irreversible damage to the surrounding tissue and local lymphatics. The overall goal of our research is to study the effectiveness of osteopathic manipulative medicine techniques (OMT) for the treatment of edema, infection and inflammation. The aim of this study was to evaluate oxazolone (OXA) as a model to induce acute inflammation and lower limb edema in the rat. Specifically, we hypothesized that a single application of OXA would induce a local inflammatory response and induce edema in the lower limb. Methods. Female Sprague Dawley rats, weighing 200-250 g, were used for this study. On day 0 the right lower limb was shaved and 750 µl of 5% OXA-acetone solution or 750 µl of a 5% phosphate buffered saline (PBS)-acetone solution vehicle (VEH) was applied to the exposed skin. Lower limb measurements were made at days 0 and 6 using a Vernier caliper. At day 6, the rats were euthanized, and the bilateral hind paws were removed above the calcaneus and weighed. The spleen and bilateral inguinal lymph nodes were removed, homogenized, centrifuged and cells were stained with phycoerythrin (PE) mouse anti-rat granulocytes, fluorescein (FITC) anti-rat CD3, and allophycocyanin (APC) anti-rat CD161 antibodies. The percentage of granulocytes, T cells and dendritic cells were measured by flow cytometry. Data were analyzed by analysis of variance (ANOVA) followed by Tukey-Kramer post-test or by Student's t-test. Comparisons were made between OXA and VEH groups at day 6 post-induction. Results. OXA did not induce significant (p[greater than]0.05) changes in either hind paw thickness or hind paw volume. OXA significantly (P[less than]0.05) increased the concentration of macrophages, neutrophils, and dendritic cells, and T cells within inguinal lymph nodes. Conclusions. OXA induced an acute local inflammatory response in the draining inguinal lymph nodes. However, as used in this approach, OXA did not induce peripheral edema. In future studies we will investigate alternate strategies to induce lower limb edema in the rat.