904 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TOSE CYCLE I co 2 GLYCOGEN -I GLUCOSE LACTATE • (CELL) I I I I I I J E-M PATHWAY GLUCOSE (Blood) Carbon dioxide arises via the pentose cycle, pyruvate decarboxylation, and the TCA cycle (Fig. 1). One method of showing that glucose is utilized through the TCA cycle is the use of inhibitors of the TCA cycle and oxidative phosphorylation, such as malonate, cyanide, and amytal. It was found that all of these inhibitors decreased CO2 pro- duction, an indication that the TCA cycle is operative in the hair fol- licles. Participation of the pentose cycle can be demonstrated by the use of C-1 and C-6 position labeled glucose. The carbon at position 1 in the glucose molecule contributes to CO2 production through the penrose cycle, the EMP, and the TCA cycle, but at position 6 in glu- cose the carbon produces CO2 primarily through the EMP and the TCA cycle (Fig. l). Thus, the ratio of •4CO• formation from C-1 to that from C-6 glucose exceeds one when the pentose cycle is active. A ratio far above one in the growing hair follicles indicates that glucose is utilized actively via the pentose cycle (Table I). This large contri- trotion of the pentose cycle to glucose catabolism is one of the charac- teristics of growing hair follicles. r• c02 YL CoA J, FATTY ACIDS CO 2 Figure 1. Schematic representation of the pathways of glucose metabolism

HUMAN HAIR FOLLICLES 905 Table I •4CO.• Production from C-1 and C-6 Labeled Glucose-•4C by Hair Follicles Hair Follicles Growing Resting CO., From N • = 4 N • = 3 C-1 C-6 Ratio C-1/C-6 cpm (4- SE)/hr/mg wet wt 2010 (+ 75.6) 697 (+ 81.9) 195 (+ 18.5) 197 (+ 21.7) 10.5 (4- 1.03) 3.6 (4- 0.64) • Number of experiments. Each experiment represents an average of quadruplicate tubes (12). In previous experiments, metabolic inhibitors were used to demon- strate the occurrence of the TCA cycle. Since under physiological con- ditions the overall metabolic processes are in a steady state, the use of a potent metabolic inhibitor may alter normal pathways. Therefore, to analyze quantitative changes in the major glucose pathways in hair follicles, we applied the method proposed by Wood et al. (14) and later extended by Katz et al. (15) and Rognstad and Katz (16). This method does not require the addition of any metabolic inhibitor. Typical results of the quantitative study are summarized in Table II data on the metabolism of skeletal muscle (17) are also listed for comparison. Interestingly, hair follicles have a faster glycolytic rate and an apparently slower respiration rate than muscle. Another re- Table II Glucose Metabolism of Hair Follicles Hair Follicles Growing Resting Muscle" Glucose utilized (mt• moles/mg wet wt/hr) 17.2 Lactate formed (specific yield, % of total glucose utilized) CO2 formed (%) from C14-U-glucose 3.7 C14-l-glucose 7.5 C14-6-glucose 0.56 Pentose cycle contribution (%) 2.5 Other synthetic pathways from glucose (lipids, glycogen, DNA, protein) (%) 1 90 •-• 98.5 8.5 7.2 90 •-• 98.5 65 2.0 5 2.•} Equal 1. 0.6 0.5 1 Data from Beatty et al. (17).