Diurnal changes in murine spermatogenesis.

We analysed testicular samples of NMRI mice every 2 h of a day in order to determine whether there is a circadian rhythm in spermatogenetic activity. We used flow cytometry after staining the DNA with DAPI. The highest proportion of DNA synthesizing cells (mainly spermatogonia and preleptotene spermatocytes) was seen at 8 p.m. and especially at 10 p.m.; the lowest proportion was observed at 2 p.m. At 6 a.m., the percentage of round spermatids increased significantly, whereas the fraction of 4c-cells decreased at that time. Our results of a diurnal rhythm of spermatogenic DNA synthesis rate are in contrast to another publication of other authors (Oakberg and Crosswait, 1983).