Effect of Pro-inflammatory Cytokines on Interstitial Fluid Pressure in Gingiva

Lowering of interstitial fluid pressure (P_if) in the initial stages of several inflammatory reactions is an important factor that explains the rapid edema formation in acute inflammation. IL-1b and TNFa are pro-inflammatory cytokines produced by stimulated monocytes/macrophages during the initial stages of inflammation. Increased levels of these cytokines are involved in the pathogenesis of gingivitis, characterized by edematous swelling of the gingiva. It has been shown previously that IL-1b and TNFa  induced increased negativity of P_if in rat paw skin suggesting involvement in development of edema. Objectives: to test if IL-1b and TNFa induce lowering of P_if in the rat gingiva. Methods: P_if was measured at the free gingiva of the maxillary incisors of anesthetized female Wistar rats (n=26) using micropipettes (5-10 mm) connected to  servocontrolled counterpressure system. After intravenous administration of either 0.5ml vehicle (physiologic saline with 1% albumin, n=7), or TNFa (400ng/ml, n=9) or IL-1b (30ng/ml, n=10) the animals were kept alive for 1-3 min before cardiac arrest was induced with saturated KCl i.v. Rats were killed in order to limit fluid filtration and edema formation thereby avoiding underestimation of  P_if. P_if was repeatedly recorded for 60min after death. The recorded pressures were averaged and statistically analyzed (RM-ANOVA, Bonferroni).  Results: P_if measured in alive and after cardiac arrest (ca):

P_if is reported in mmHg, data are means±SE, * p<0.05 compared with alive, ¶ p<0.05 compared with 1% albumin at same time interval. Conclusion: intravenous administration of IL-1b and TNFa induced lowering of P_if in rat gingiva after 40min when compared with alive and was significantly lower than controls after 60min. Our observations suggest that these cytokines are involved in edema formation during inflammation in gingiva.