The diurnal fluctuations in unincorporated radio-thymidine pool and its relation to the circadian rhythm of thymidine incorporation in mouse pinna skin.

The circadian variation in the labelling indices of epidermal basal and sebaceous gland cells in murine pinna is a well documented phenomenon. This, however, observes only the incorporated label and takes no account of any rhythmic changes in the precursor pool. It is reported here that, using a liquid scintillation counting method, there is a diurnal change in the level of unincorporated radio-labelled thymidine, which is apparently not related to the rhythm of thymidine incorporation. The implications of this phenomenon and its relationship to DNA synthesis are discussed.