Circadian rhythms in neonatal rat parotid gland acinar cell and ileal crypt cell mitosis.

Mitotic activity of parotid gland acinar cells and ileal crypt cells was analyzed over the course of a 26-hour period at 8 and 15 days after birth. At 8 days there is no detectable circadian rhythm of mitosis in either tissue while at 15 days after birth there is a mitotic rhythm with an amplitude of 36.8% in ileum and 26.5% in parotid gland. Possible factors which may influence and initiate circadian rhythms are discussed.