Endocrine rhythms associated with pineal gland function

It seems that one of the most important functions of the pineal gland may be to synchronize breeding activity in seasonal breeders with the appropriate time of the year. In the absence of this important gland, daylength is unable to exert an influence on reproductive physiology, and either no seasonal rhythm in reproduction occurs (e.g., in hamsters) or the rhythm free runs (e.g., in ferrets). In the latter case the breeding period comes out of phase with the appropriate season of the year. Whether daily rhythms in endocrine functions are synchronized or impelled by pineal secretions remain, for the most part, unclear. Certainly, the rate of secretion of prolactin during the night seems to depend upon an intact pineal gland.