Studies on the structure of the vitreous body: VIII. Comparative biochemistry

Abstract

A comparative biochemical study was made on the vitreous body of the following animals: squid, frogs, tortoises, chickens, turkeys, pigeons, owls, rabbits, guinea pigs, sheep, cattle, and owl monkeys. It was found that: 1. 1. The vitreous body of the squid is a liquid and has a low viscosity. The vitreous body of the owl monkey is a viscous fluid. In the chicken, turkey, and pigeon, the posterior part of the vitreous body is a liquid; the rest is a gel. In the other animals the vitreous body is in gel state. 2. 2. The total ascorbic acid content is high (in the order of 10 mg./100 ml.) in adult mammals and tortoises, and it is ten times lower in the other animals investigated. The amount of oxidized ascorbic acid in mammals is about 10% of the total ascorbic acid content. 3. 3. Only when the vitreous body is in gel state does it contain collagen which can be sedimented by high-speed centrifugation. 4. 4. Hexuronic acid is present in the vitreous body of all species, but with a large variation in concentration. The highest values were found in squid and in some mammals (cattle, owl monkeys, sheep). Its concentration is much less in birds, rabbits, and guinea pigs. In frogs no hexuronic acid could be determined. 5. 5. In most animals the hexosamine concentration was higher than the hexuronic acid, indicating that hexosamine-containing compounds other than hyaluronic acid, such as glycoproteins, are present. The sialic acid content supports these findings. 6. 6. The aqueous humor of birds contains hexosamine and hexuronic acid in about the same concentrations as the vitreous body. The aqueous humor of the owl showed an uneven distribution of hexosamine and hexuronic acid. A viscous layer, presumably hyaluronic acid, was found behind the cornea. The hyaluronic acid concentration of the aqueous humor of the mammals investigated was 100 times less than that of the vitreous body. 7. 7. In all animals the soluble protein concentration of the vitreous body is very low (about 1% of the serum concentration), indicating that there is a distinct barrier between the vitreous body and the blood vessel system. 8. 8. Hyaluronic acid, soluble proteins, and collagen were unevenly distributed in the vitreous body of all animals investigated.