Modulation of dermal cell activity during hair growth in the rat.

Interaction between connective tissue cells and hair growth in the rat has been studied by radioautography after in vivo and in vitro pulse labelling with thymidine, uridine, histidine, leucine and proline. The connective tissue, which surrounds and integrates the hair bulbs as a unit, contains cells of various types which have a cyclic metabolic activity. This cyclic activity is coordinated with the hair growth cycle. The number of nuclei which actively synthesize DNA in the dermal cells, mainly those of endothelial and migratory cells, significantly increases during the short and transient anagen 4 substage. RNA and protein synthesizing activities are also present in all cell types and seem modulated by the hair cycle although to a lesser degree. This data provides an important basis for the interpretation of similar studies in alopecia areata.