HUMAN HAIR FOLLICLES 907 Table IV The ATP Balance Growing Resting (t•moles/100 t•moles glucose utilized) Utilization Hexokinase 100 100 P-fructokinase 97.5 99.8 Ac. CoA carboxy. 1.0 1.0 Ac. CoA transfer Sum ca. 200 ca. 200 Formation G-3-P DH 197 201.5 Pyruvate kinase 197 199.6 Pyr. DH (P/O = 3) 23 19 TCA cycle 78 57 Sum ca. 500 ca. 480 Net -3-300 -3-280 Table V Pyridine Nucleotide Balance (Cytoplasmic) Hair Follicles Growing Resting (t•moles/100 t•moles glucose utilized) TPNH DPNH TPNH DPNH Formation Pentose cycle 15.0 ... 3.6 ... G3P DH ... 197 ... 200 Utilization Fatty acid synthesis 1.6 ... 1.1 ... Glycerol ... 0.2 ... 0.2 Lactate ... 190 ... 193 Net 13.4 6.8 2.5 6.8 for growing follicles are twice those for resting, because the growing ones utilize glucose about twice as fast as the resting. The net shifts in the metabolic pathways during the transformation of the resting into the growing stage of hair follicles can be summarized as follows: compared with that in resting follicles, glucose utilization in growing follicles in- creases 200%, glycolysis 200%, activity of the penrose cycle 800%, metabolism by other pathways 150%, and ATP production via the res- piratory chains 270%. Thus, in the growing hair follicles, glucose

908 .JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS assimilation produces not only sufficient energy for the follicles to [unction but also essential substances [or the follicle to metabolize fatty acid, nucleic acid, and steroid hormones. Several enzyme activities of both the sheath and bulb portions of hair follicles at different stages of hair growth were assayed with the microenzyme assay methods developed by Lowry (18-20). Thin sec- tions (20-50 •) of skin biopsies were first freeze-dried and small hair fol- licle samples (0.5 to lvg) were dissected under the microscope. The en- zyme activities were assayed by highly sensitive fluorometric measure- ments (20) within the limits at which the reaction rates were directly pro- portional to the reaction time as well as to the amounts of enzymes (11). The enzyme activities in all of the ariagert phases thus far studied are about the same (Fig. 2). However, there are conspicuous differences be- ENZYME• AGE HEXOKINASE PHOSPHORYLASE TELOGEN ANAGEN 'Fl. Trl' ANAGEN • ANAGEN • G6P DH G3P OH LDH FUMARASE Figure 2. Enzyme activities at different stages of the hair cycle. Each enzyme activity in the upper sheath at telogen stage is arbitrarily taken as 100% (i.e., three bars indicate 300% increase). White bars represent enzyme activities in the external sheath and black bars those in the bulb portion (12). (G3PDH z glyceraldehyde-3-phosphate dehydrogenase LDH = lactate dehydrogenase)