Maternal melatonin communicates daylength to the fetus in Djungarian hamsters.

Daylength (photoperiod) influences the rate of reproductive development in the juveniles of some photoperiodic species. Recent studies show that daylength during the prenatal period is perceived by the fetus and that this perception can profoundly influence postnatal reproductive and somatic development. Using the photoperiodic Djungarian hamster, we assessed the role of the maternal pineal gland and its hormone, melatonin, in this prenatal perception of daylength. Maternal pinealectomy eliminated the influence of prenatal photoperiod on testicular and body weights of male pups, suggesting that a product from the maternal pineal gland communicates daylength to the fetus. Infusion of the pineal hormone melatonin into pinealectomized dams for various durations during gestation mimicked the effect of varying the prenatal photoperiod on both testicular and body weights. These results indicate that pineal melatonin is involved in this novel form of communication from mother to fetus.