HUMAN HAIR FOLLICLES 903 Mammalian hair follicles have their own autonomous growth cycles. During the growing stage (anagen) of the hair cycle, the follicles de- velop when hair is formed by the matrix of the follicle, growth ceases, and the follicle is in the resting stage (telogen). After a specific period of quiescence, these processes resume autonomously. As far as the energy requirement is concerned, one can assume that the growing hair follicles synthesizing keratin require much more energy than the resting ones. Thus, the pathways to yield adenosine triphosphate (ATP), a chemical form of energy, should be accelerated to meet this requirement. The specific aim of the first experiment was to study the pathways of energy- producing systems and to examine the changes in these pathways during the different functional stages of the hair follicles. In man and most subhuman primates, growing and resting hair fol- licles are randomly present at the same time in the same region. The potential difficulty in sampling the hair follicles was avoided by use of the plucking method (10). In plucking, the root of the hair follicles is attached to the end that of the growing follicles consists of a small epithe- lial sac. Freshly plucked hair follicles from the scalp of Japanese donors, none of whom showed any evidence of baldness, were used for the follow- ing metabolic studies. Generally, 3 growing or 5 resting follicles were transferred into a microrespiration tube of 2.5-mm i.d. and 30-mm length containing 0.06 vc of u-•4C, or 1-14C, or 6-•4C labeled glucose in 3 v1 of buffered glucose Krebs-Ringer bicarbonate solution pH 7.4 (with a final glucose concentration of 100 mg/100 ml). After an appropriate in- cubation period, various end products such as CO2, lactate, lipids (fatty acids in some cases), glycogen, DNA, and protein (as residue) were iso- lated, and their radioactivities were counted with a scintillation appara- tus (11, 12). In many tissues and organs, the common source of energy is glucose, which is carried by the blood to the local sites. Subsequently, glucose permeates cell membranes, becomes phosphorylated, and is then directed through various pathways, the major ones being the Embden Meyerhof pathway (EMP), the pentose cycle, and the tricarboxylic acid (TCA) cycle (Fig. 1). Qualitative proof that hair follicles utilize glucose through these major pathways came about without complication. After the hair follicles had been incubated with three types of glucose-•4C, lactate-•4C, the end product of EMP, was isolated, and the presence of all enzymes participating in the EMP was demonstrated (12, 13). Also, the •4CO,• resulting from the labeled glucose was trapped in all experiments.

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