HUMAN HAIR FOLLICLES 911 % conversion AD 7 D #K GROWING (3) AD AD D D SA ST GROWING GROWING (4) (4) AD SK SA RESTING RESTING (I) (2) /J mole/100 mg/hr I0,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 AD U 1,000 AAD DHT •{•111• ST RESTING Figure 3. In vitro metabolism of testosterone-•C by human hair follicles. The rate of each metabolite formation is exprcssed as % conversion of the total-•C per hour and also as •mols per 100 mg hair follicles wet weight per hour incubation. Each bar is an average of (N) experiments on 3 subjects, geK, geA, and geT. (DHT : 5a-dihydrotestosterone AD • androstenedione AAD -- androstanedione and U • unidentified substance) compared on a weight basis). The rate of 5a-dihydrotestosterone formation appears to be much faster in the growing than in the resting hair follicles, as compared on a weight basis. Hence, the net formation of this tissue-active androgen per hair follicle is obviously much greater in the growing than in the resting hair follicles. Figure 4 shoves the results of the enzyme assays. The enzyme activities are measured on frozen-dry preparations with TPNH added as a colactor. A potential activity of testosterone catabolism to androstenedione was also measured simultaneously with the addition of DPN+. Under the assay condition employed in this experiment, the addition of DPN+ does not interfere with 5a-reductase assay. Again, the major catabolite is androstenedione in both types of hair follicles and the catabolic rates per tissue weight are faster in the •owing than in the resting hair follicles. It is signifi- cant to note that the growing hair follicles can produce this tissue-ac- tive androgen at a rate comparable to that of the prostate (27, 28). Comparison of the results from these two types of experiments re- veals that in the growing hair follicles the rate of 5.wdihydrotestosterone formation by the frozen-dried tissue with added cofactors appears to be slightly faster than that by fresh hair follicles without cofactors. In the

912 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ,u ,u mole/lOOmg/hr 26,000 24,000 22,000 20,000 18,000 16,000 14,000 12,000 io,00o 8,000 6,000 4,000 2,000 AO AO AD AD 0 D GROWING GROWING GROWING GROWING (Z) (2) (5) Figure 4. 5a-Reductase activities of growing and resting hair follicles. Average of (n) experiments. Abbreviations same as for Fig. 3 resting hair follicles the rate of active androgen formation is greatly increased by addition of the colactor, TPNH. These data, therefore, suggest that the growing hair follicle can generate sufficient TPNH from a carbon source while resting follicle cannot hence the endog- enous level of TPNH in the resting follicles is the limiting factor. As indicated in the preceding section, the most remarkable metabolic shift occurring during the transformation from the resting to the grow- ing hair follicles is the marked increase in the cytoplasmic TPNH level (Table V). Ultramicromeasurements of pyridine nucleotides by the cycling technique (31) a•ee with our previous calculation of the Table VI Analysis of Human Hair Follicles (Bulb Portion) for Pyridine Nucleotides by the Cycling Technique" Growing Resting TPN + 38 32 TPNH 89 53 DPN + 394 240 DPNH 644 377 "Results represent means of 5 determinations, expressed as tztzmoles/mg dry weight. (TPN + triphosphopyridine nucleotide DPN + = diphosphopyridine nucleotide TPNH and DPNH reduced TPN and DPN).