Edema-preventing mechanisms in rat gingiva

Abstract

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 ¹²⁵I-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, 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 ¹²⁵I-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.

Key Words:

• Capillary filtration
• colloid osmotic pressure
• edema
• lymph flow
• microcirculation
• tissue pressure