Enzymes in lymph: a review.

Lymph is the minute net volume of contending hydrostatic and osmotic capillary forces. It is built up extravasculary in tissues and reaches the intravasal space by definite lymph collecting vessels, which enter the venous system at the angulus venosus at the root of the neck. Sampling methods for lymph from individual tissues or from lymph collecting vessels of man and various animals are cited and the preparation of lymph for enzymatic analysis is described. The extracellular distribution and transport of enzymes is important for diagnostic enzymology, because enzymes released from cells in continuous physiological processes, or after injury to the tissue, reach the intravasal space mainly via the lymphatics. This is evident from the high lymph-plasma ratios of diagnostically important enzymes. The type of enzyme transport (lymphatic or by direct interstitial-venous entry) depends on the heterogeneity of the capillary barrier characteristic of the different organs. The permeability is extremely high in liver, i.e. enzymes in hepatic lymph originate mainly from blood, which they have reached through the large openings in the sinusoidal endothelial lining; in contrast the permeability is extremely low in skeletal muscle, where lymphatic transport therefore predominates. The phenomenon of increased enzyme activities in plasma after physical exertion is explained by alterations of lymph flow. A table gives a survey of enzyme activities, lymph-plasma quotients, and lymph flow from lymph vessels of various tissues as well as from the lymph collecting vessels of man and animals, with comments on the signficance for diagnostic enzymology.