E. Glasius

The origin of some enzymes in tear fluid, determined by comparative investigation with two collection methods

Abstract Comparative investigations of human tear fluid, collected in capillaries as well on filter paper strips, revealed that the enzymes lactate dehydrogenase (LDH), malate dehydrogenase (MDH), pyruvate kinase (PK), isocitrate dehydrogenase (ICDH), aldolase (ALD), glucose-6-phosphate dehydrogenase (G-6-PDH), sorbitol dehydrogenase (SDH), glutamate dehydrogenase (GLDH) and glutamate-oxalacetate transaminase (GOT), are not secreted by the lacrimal gland, but can be liberated into tear fluid after slight damage of the conjunctival and corneal epithelium. Hexokinase (HK) and glutamate-pyruvate transaminase (GPT) and the lysosomal enzymes α-galactosidase (α-gal) and β-hexosaminidase (β-hex), which are produced by the lacrimal gland, may be present in increased amounts after slight epithelial damage. A practical application of these findings is discussed.

Collection method dependant concentrations of some metabolites in human tear fluid, with special reference to glucose in hyperglycaemic conditions

Concentrations of the metabolites glucose, lactate, pyruvate, and urea were determined in human tear fluid. Collection of the tears in glass capillaries, without mechanical irritation, permitted the estimation of naturally occurring levels of these metabolites. Glucose concentrations were very low, also in diabetics with high blood glucose levels. Lactate was present at higher levels and pyruvate and urea in about the same concentrations as normally for blood. Collection of the tears with filter paper strips as absorbent material caused slight epithelial damage and consequently a loss of the barrier function of the epithelium. In filter paper eluates glucose concentrations were found to be much higher, especially in diabetics with high blood glucose levels. Lactate and pyruvate concentrations were not influenced, whereas the urea concentrations decreased. The value of clinical tear glucose tests is discussed.

Selective properties of the vitreous barrier

Experiments with several groups of chemically related substances showed that differences in penetration into the vitreous body of the rabbit must be attributed to the existence of a vitreous barrier. More than one mechanism is involved in the function of the vitreous barrier, one of which is selective in respect to lipoid solubility, while another mechanism responds to the electrical charge of molecules.

The peroxidase-thiocyanate-hydrogenperoxide system in tear fluid and saliva of different species

Abstract The occurrence of peroxidase (POD) and thiocyanate in saliva and tears of humans and different animals is not so common as would be expected for a generally acting POD-thiocyanate-hydrogenperoxide antibacterial system. Moreover there does not appear to exist any correlation between salivary or lacrimal POD activity and the thiocyanate concentration in these secretions. In fact only in human and guinea-pig saliva are the requirements fulfilled for an effective antibacterial action. The secretions in other species contain no demonstrable POD activity (rabbit) or too low a thiocyanate concentration (cat, guinea-pig, human, rat). The function of the POD-thiocyanate-hydrogenperoxide system as an alternative for the bacteriolytic enzyme lysozyme, which is lacking in the secretions of species other than human and some monkeys, must be excluded.

Cholesterol in human tear fluid.

Abstract Small and varying amounts of cholesterol and cholesterol esters were found in human tear fluid. Failure to establish a relationship between the cholesterol concentrations of plasma and tears is in accord with the concept that the origin of these lipids is not to be found in the lacrimal gland, but in the Meibomian gland. The “oily substance” sometimes found on contact lenses in patients with contact lens problems, is not related to cholesterol or to elevated cholesterol levels in tear fluid.

A comparison of the effects of non-steroidal compounds on the disruption of the blood-aquous barrier

The anti-inflammatory agents, diclofenac, flurbiprofen and indomethacin, were examined to determine their inhibitory effect on the breakdown of the blood-aqueous barrier in rabbit eyes, following paracentesis. In treated eyes, compared to the non-treated eyes, the increase in protein and fluorescein in the secondary aqueous was inhibited in a dose-dependent manner. Dose-response curves for the non-steroidal compounds were comparable and were in the range of 3×10−6–10−2 m . However, indomethacin did not completely inhibit the breakdown of the aqueous barrier. The observed effects were strongly dependent of the pH of the vehicle and partly correlated with lipid solubility of the agents.

Urea and the vitreous barrier of the eye.

Massive infusion of urea in rabbits demonstrated that the uneven distribution of urea over the eye has its origin in a different speed of penetration of urea into the tissues. No characteristic physico-chemical properties can be attributed to the vitreous barrier on the basis of these concentration gradient, since penetration of urea seems to be restricted by secondary factors.

The effect of Indomethacin on the anterior segment of the eye after paracentesis

The prostaglandin-inhibiting effect of Indomethacin (IN) was studied in rabbits, using paracentesis as a stimulus and rise in aqueous protein and fluorescein concentration after intravenous fluorescein injection as parameters. In eyes pre-treated with IN eye-drops the rise in fluorescein and protein concentration in the secondary aqueous was less than in the control eyes; the rise in the control eyes was less than in the eyes of rabbits not treated with IN. There was a good correlation between the rise in protein and the rise in fluorescein concentration in the secondary aqueous.The four different 0.5% IN suspensions used showed different PG-inhibiting activity, attributed to the difference in physicochemical composition.

Amylase in human tear fluid: origin and characteristics, compared with salivary and urinary amylases.

Abstract In the tissues, coming in contact with the tear fluid, amylase activity is only demonstrable in lacrimal gland tissue and this is in accord with the concept that the lacrimal gland is the source of tear amylase. Isoenzymes of amylase in human tear fluid were separated with agarelectrophoresis and demonstrated with an iodine-starch method. The isoenzyme pattern of tear fluid amylase was different from that of urine and saliva. The influence of pH in the range 6–8 and of the ionic activators Ca 2+ and Cl − also indicated different behaviour of the amylases.

Enzymatic studies in lacrimal secretion

Abstract The activity of the enzymes: lactate dehydrogenase (LDH), pyruvate kinase (PK), malate dehydrogenase (MDH), amylase (AM) and lysozyme (LZM) was studied during lacrimation in healthy persons. The activity of the enzymes of energy-producing metabolism: LDH, PK and MDH fluctuated in parallel with each other. Fluctuations in AM activity showed no correlation with other enzymes and LZM concentrations remained rather constant. The origin of these enzymes in the process of lacrimal secretion is discussed.