Effects of Photoperiod and Subcutaneous Melatonin Implants on the Reproductive Status of Adult White‐footed Mice (Peromyscus leucopus)

The reproductive consequences of photoperiod and melatonin administration were compared in adult white‐footed mice (Peromyscus leucopus). Animals were exposed either to a long photoperlod (16 hours of light:8 hours of dark) with and without subcutaneous melatonin—beeswax implants or to a short photoperiod (8 hours of light:16 hours of dark) for six weeks. Following treatment with either a short photoperiod or melatonin, testicular weights and volumes as well as plasma testosterone levels were significantly (P < 0.01) reduced relative to animals maintained under long daily photoperiods without melatonln Implants. Under the conditions of the present study, chronic melatonin administration is as repressive to the reproductive status as is a short photoperlod in adult white‐footed mice. 1981 American Society of Andrology