The rat hair cycle produces rapid anatomical and physiological changes in the entire skin. By the 4th day of the cycle, the epidermis has doubled in thickness.

The present study shows that, during this proliferative period, there is a correlation between the biological state (growth) and the molecular composition (enzyme concentrations) of the epidermal cell. In proliferated 4th day epidermis there has occurred not only an increase in the number of viable cells but also an increase in succinic dehydrogenase and cytochrome oxidase activity and ribonucleic acid (RNA) content in the viable epidermal cell. Moreover, RNA content and enzyme activities appear to be correlated.

The significance of these findings is discussed in the light of recent evidence supporting the relationship between RNA and enzyme synthesis and the role of hormones in the induction of enzyme adaptation.

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