Mitotic index of type B spermatogonia in intact animals is characterized by a circadian rhythm. Mitotic index increased and its circadian rhythm disappeared after pinealectomy. Treatment with Epithalamin for 14 days restored the circadian rhythm. The circadian biorhythm of spermatogonia proliferation suggests the presence of circadian rhythm of spermatogenesis in general and its regulation by the pineal gland.

The mitotic index of spermatogonia and 24-h dynamics of stages IV, VI, and XIV of spermatogenic cycle are characterized by circadian rhythm. No circadian rhythm was detected for 11 of 14 stages. Pinealectomy led to an increase of the mitotic index of spermatogonia but did not modulate the incidence of spermatogenic cycle stages, and led to disappearance of the circadian rhythm of both the mitotic index and spermatogenic cycle stages.