Change in Hair Cycle and Hair Length in Nude Mice by Administration of Deuterium Oxide

D2O increased hair length in Balb/c nu/nu (nude) mice in our previous study although it has an antimitotic effect in cells. To investigate the mechanism of the effect on the hair length, we examined the change by the administration of D2O in the duration of the hair cycle and the proliferating activity of the hair matrix in relation with hair length in nude mice. The results showed that 20 or 30% D2O administration did not change the gross structure of the hairs, the proliferative activity and keratinization of the hair matrix cells, but elongated the hair cycle. The duration of the hair cycle increased by the administration of D2O in a dose-dependent manner over the examined range and these effects were reversible by discontinuation of D2O. The change in the hair length correlated with the change in the hair-existing phase particularly. We also showed that the mast cell density in the skin, which is related to the hair cycle, increased in the deuterated mice at anagen VI stage which nearly corresponds to...