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).

906 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS markable difference between hair follicle and muscle metabolism is in the pentose cycle activity, which is insignificant in muscle. The metabolic characteristics of growing and resting hair follicles differ remarkably. Growing hair follicles utilize glucose twice as fast as those resting. Although lactate is the major product in both types of hair follicles (specific yield being 90 to 99(•o), the rate of lactate pro- duction in the growing follicle is double that in the resting. The calculated contribution of the pentose cycle to glucose utilization in the growing follicle is four times that in the resting (Table II). A bal- ance sheet of glucose carbon utilization further illustrates the differ- ence between growing and resting hair follicles and shows that the pentose cycle activity in the growing follicles is about 400% greater than that in the resting follicle (Table III). The contribution of both the TCA cycle and the pathway to fatty acid synthesis also appears to be increased. Table IV compares energy production in the growing and resting hair follicles. In both types, one mole of glucose yields a net of about 3 moles of ATP, roughly two-thirds from cytoplasmic me- tabolism and one-third via the respiratory chains. Energy production in hair follicles is not very efficient, most of the glucose being converted to lactate. However, the activity of the TCA cycle increases about 35% during the growth stage of the hair follicle. The pyridine nucleotide balance is shown in Table V. The increase in reduced triphosphopyri- dine nucleotide (TPNH) formation in the growing follicle is marked. In Tables III and IV, the ATP and carbon balance charts are based on the utilization of 100 vmoles of glucose. However, the actual values Table III The Carbon Balance Growing Resting Products (t• atom carbon/100 t•moles glucose utilized) -- CO2 from Pentose cycle 7.5 1.8 Py. decarboxy. 7.5 5.5 TCA cycle 13.0 9.5 Lact ate 5 69 5 81 Fatty acids 1.8 1.3 Glycerol 0.6 0.5 Glycogen 2.5 1.2 DNA protein 2.5 2.6