Ascorbic acid and healing of heat injuries in the guineapig cornea.

It is accepted that the repair of connective tissue is defective in scurvy. Wounds of the cornea, however, may be superficial, involving only the epithelium, or they may be deep and invade the collagenous substantia propria. Moreover, the power of proliferation of the epidermis is not impaired in scurvy (Wolbach & Howe, 1926); in keeping with this finding, Galloway, Garry & Hitchin (1948-9) found that eye wounds, produced mechanically and confined to the corneal epithelium, healed with undiminished speed in guinea-pigs maintained on a deficient intake of ascorbic acid. The epithelium covering the cornea is said to heal by proliferation and migration of epithelial cells, SO that no new formation of collagen is required (Arey & Covode, 1943; Buschke, Friedenwald & E’leischmann, 1943 ; Mann, 1944). The present investigation was designed to study and compare the rate of healing of both superficial and deep corneal wounds in normal and in subscorbutic guinea-pigs. Another factor may be of importance; ascorbic acid is known not to be uniformly distributed throughout the body, and it seems to have a very selective distribution within the cornea itself, although its exact location is by no means settled. Schmid & Biirki (1943), using a histochemical method, found the greatest concentration in the superficial epithelial layers of the cornea. The substantia propria had a lower content, although there was a high concentration in the region of Bowman’s and Descemet’s membranes. Henkes (1946), on the other hand, who extracted and titrated ascorbic acid from various regions of the cornea, found no ascorbic acid in Bowman’s membrane, a little in the corneal epithelium and a high concentration in the substantia propria and in Descemet’s membrane. The subepithelial portion of the substantia propria contained the highest concentration of vitamin C. Of importance for our work was the fact that, in experimental scurvy in guinea-pigs, the ascorbic acid disappeared from the cornea in from z to 3 weeks, although the glutathione content remained unchanged. Pirie (1946), using microtitration, found the concentration of ascorbic acid to be greatest in the corneal epithelium. Such findings made it essential that all our experimental guinea-pigs should start with a uniform high content of ascorbic acid. Half the animals had then to receive a diet calculated to produce a subscorbutic state over a period of time necessary to allow the ascorbic acid to disappear from the tissues of the cornea. To maintain complete saturation of the tissues of a guinea-pig with ascorbic acid Kellie 8i Zilva (1939) believe that 20 mg. by mouth daily is necessary. However, as small a dose as z mg. daily