EDEMA-PREVENTING MECHANISMS IN RAT GINGIVA

The long-term effect of increased local venous pressure (P(v)) on interstitial fluid pressure (P(i)), colloid osmotic pressure (COP(i)), and fractional removal rate of I-125-labeled human serum albumin (k(Alb)) was studied in rat gingiva. Measurements were performed on experimental animals and sham-operated controls up to 4 days after ligation of jugular veins. On the day of ligation P(v) in the facial veins rose from 2.5 +/- 0.3 (SD) to 15.8 +/- 2.8 mm Hg and stayed at about this level for 2 days before a decrease to 7.4 +/- 0.9 mm Hg on day 4. In free gingiva P(i) rose from an average of 3.5 +/- 0.4 to a maximum of 6.3 +/- 0.7 mm Hg, whereas in attached gingiva the corresponding increase in P(i) was from 6.0 +/- 0.7 to 11.1 +/- 2.1 mm Hg. One day after the ligation COP(i) in wick fluid from gingiva was reduced from the control level of 10.6 +/- 1.4 to 4.5 +/- 0.9 mm Hg. COP in plasma and COP(i) in subcutaneous tissue on the back were unaffected. The removal rate of I-125-labeled albumin (k(Alb) from the gingiva showed a nearly threefold increase after venous ligation, from 0.073 +/- 0.01 to 0.211 +/- 0.06 h-1. It is concluded that in free and attached gingiva, both a rise in P(i) and a decrease in COP(i) will counteract the increased filtration pressure and thus prevent edema formation during venous stasis. The fall in COP(i) is most likely due to increased lymph flow and not dilution, as venous stasis significantly increased k(Alb) without any visible increase in gingival volume.