Metabolism of connective tissue lactic and citric acid formation by skin.

In a previous publication (1) the significance of lactic and citric acid synthesis by bone was discussed. Acid formation by other connective tissues such as cartilage (2, 3) cornea (4), and lens (5-7) has also been demonstrated. The presence of the glycolytic enzymes in skin and the formation of lactic acid have been demonstrated by several investigators (8-12). Although Dickens (13) found that skin contained citric acid, the actual synthesis of citric acid by skin has not been previously demonstrated. Barron et al. (9) were unable to demonstrate the utilization of citrate by skin slices in vitro, as shown by measurements of oxygen consumption and by chemical analysis. These investigators concluded that the tricarboxylic acid cycle was inoperative in skin. Griesemer and Gould (14) were also unable to demonstrate any utilization of citrate by skin homogenates but did find an increase in oxygen uptake in the presence of other intermediates of the tricarboxylic acid cycle. Freinkel (10) likewise concluded that the Krebs cycle was relatively unimportant in skin. On the other hand, Cruickshank et al. (15) demonstrated the presence of isocitric dehydrogenase in skin and concluded that the Krebs cycle was highly active in this tissue. The present studies were undertaken in order to clarify the status of the tricarboxylic acid cycle in skin. Additional information has also been obtained concerning the dynamics of glucose utilization, and the accumulation of lactic and citric acids by this tissue.