Effect of histamine and bradykinin on lymph and tissue fluid composition in the rabbit hindlimb: evidence for two compartments in tissue fluid.

In the rabbit hindleg lymph and tissue fluid were collected before and during close intraarterial infusions of histamine (2.5 and 10 micrograms/min) or bradykinin (0.4 microgram/min). Protein concentration was higher in the tissue fluid than in the lymph. During the 2h of the experiment in the control animals protein concentration increased in the lymph and decreased in the tissue fluid. Lymph flow decreased in the controls and it was not significantly influenced by histamine but was in the majority of animals (14 of 20) grossly augmented by bradykinin. Lymphatic protein and LDH fluxes were increased both by bradykinin and histamine. In animals where the vasoactive agents failed to alter lymph flow LDH concentration in the lymph increased significantly without comparable changes in the tissue fluid. On the other hand, in experiments where lymph flow was increased lymphatic LDH activity decreased but the activity in tissue fluid remained unchanged. It is concluded that the interstitial fluid is composed of two compartments. Only the perivascular compartment of tissue fluid is drained directly by the lymph vessels and lymph is essentially a recent microvascular filtrate. The second compartment of the interstitial fluid in rinsing the cells and connective tissue fibres, it is parallelly coupled and in exchange with the perivascular compartment.