Evidence for rhythms of mitotic activity in normal and adenocarcinoma cells of the renal tubules of Rana pipiens.
Kidneys were studied from 1,111 leopard frogs (Rana pipiens) after exposures to a 12-hour light-12-hour dark environment. Circadian mitotic rhythms were observed in cells of normal and spontaneous adenocarcinomatous proximal convoluted tubules from these animals. Student's t-tests verified the existence of two distinct cell populations, normal and adenocarcinomatous, in the proximal tubules. Both the mitotic variations and the t-test values were significant with P values of 0.05 or less. Mean mitotic values for the normal and spontaneous adenocarcinomatous proximal tubule epithelia were generally lower during the light-phase and higher during the dark-phase periods of the control day. The mitotic rhythm of the cancerous epithelium was almost always superimposable in outline over that of the normal epithelium during the same experimental period; i.e., the correspondence of phases of the normal and cancerous mitoses was almost identical in a single graph, although the amplitude of the cancerous mitoses was always higher. In addition to the reproducible circadian rhythms, the data demonstrated evidence for the existence of ultradian, as well as circannual rhythms.