Studies on the Incorporation of U-¹⁴C-glucose into Vitreous Polymers in Vitro and in Vivo

¹ Department of Ophthalmology, Biochemistry Research Laboratory (The Sir Isaac and Lady Wolfson Ophthalmic Research Laboratories), Hebrew University-Hadassah Medical School, Jerusalem, Israel

The incorporation of U-¹⁴C-glucose into the nondialyzable polymers of the vitreous toas studied both in vitro, with bovine tissue preparations, and in vivo, after the infusion of radioactive glucose through the lateral long ciliary artery of the cat. The radioactivity present in glucosamine isolated after Doioex 50 chromatography was taken as a measure of hyaluronic acid synthesis. It was found that cortical layer vitreous from young (4-week-old) calves was more active in converting glucose to glucosamine than equivalent samples taken from adult animals. No striking differences in biosynthetic activity were observed between the vitreous alone or with attached ciliary body, suggesting that under these experimental conditions the ciliary body does not contribute to the production of vitreous hyaluronic acid. The central (acellular) regions of the vitreous toere nearly as active as the peripheral regions in incorporating labeled glucose into nondialyzable polymers, a finding tohich could be ascribed to "extracellular enzymes" in the vitreous. Studies of the distribution of radioactivity in purified fractions showed, that most of the glucose had been utilized for the synthesis of proteins (and glycoproteins). Incorporation of radioactive glucose into nondialyzable polymers of the vitreous was inhibited by approximately 80 per cent in the presence of puromycin, due mainly to the depression of protein and glycoprotein synthesis. Very little incorporation of U-¹⁴C-glucose into hyaluronic acid occurred in vivo, although under the same experimental conditions appreciable amounts of radioactivity were found in the amino sugar moieties of the corneal mucopolysaccharides.

Key Words: vitreous • glucose • glucosamine • hyaluronic acid • protein synthesis • glycoproteins • mucopolysaccharides • cornea • puromycin • pars plana • cats