The Pineal Gland and its Function in Pregnancy and Lactation

Abstract The pineal is a neuroendocrine gland and a circadian oscillator, producing and releasing melatonin during the night and modulating a broad spectrum of physiological functions, including the female reproductive function. The pineal undergoes morphological, structural, and biochemical changes in pregnancy. Melatonin carries a photoperiodic signal from the endogenous clock, and its secretion maintains a circadian rhythm during pregnancy and lactation, with gradual increases during gestation and labor, that returns postpartum to pregestational values. Melatonin crosses the placenta unaltered or is excreted in the breast milk, thus signaling photoperiodicity in the fetus or the breastfed infant, respectively. Placenta is also an important source for melatonin, within which it exerts autocrine and paracrine actions. During labor, melatonin may synergize with oxytocin, promoting uterine contractility. Melatonin has a protective effect during pregnancy through its free-radical scavenging and antioxidant capacities, intervening to balance the oxidative challenge that accompanies the high metabolic demands during pregnancy, labor, and lactation.