The significance of tears' lactate dehydrogenase in health, and external eye diseases.

The normal values of the lactate dehydrogenase contents of tears in the presence of pyruvate and lactate as substrates were determined. The quotients of the LDH values measured in the presence of the two different substrates, and also the ratio of the subunits (H and M) of the isoenzymes, differ from the corresponding data of blood serum. In the event of external inflammatory diseases of the eye, LDHp/LDHl decreases in the tears; this deviation is enhanced by treatment with drugs inhibiting protein synthesis, primarily iododeoxyuridine. Conversely, in trachoma the ratio of the LDH isoenzymes containing mainly M (muscle) subunits are increasing. In diabetes mellitus the shift of metabolism toward the citrate cycle is reflected to a larger extent by the LDH values in the blood serum than by those in tears.