Who Plays the Strings in Newborn Analgesia at Birth, Vasopressin or Oxytocin?

, fetal human oxytocin at birth is of fetal origin, because its concentrations are higher in the umbilical artery than in the umbilical vein, and oxytocin is completely absent in cord blood of anencephalic new-borns (Chard et al., 1971). Parturition is a very complex process and oxytocin has its role particularly in contractility of myocytes (Smith, 2007). Exogenous oxytocin administration to pregnant woman strongly induces contractions (Mori et al., 2011) but plasma oxytocin does not cross placenta toward the fetus (Chard et al., 1971; Patient et al., 1999). However, by use of an in vitro system with dually perfused isolated cotyledons from term human placenta, bi-directional diffusion of oxytocin has been demonstrated across the maternal-fetal barrier (Malek et al., 1996). Fetal oxytocin concentrations have been found to be either unaffected by vaginal delivery, contractions, and by experimental hypoxic stress (Stegner et al., 1984; Thornton et al., 1993; Patient et al., 1999) or slightly increased (1.5-to 2-fold) in umbilical cord blood after vagi-nal delivery as compared to elective cesar-ean section (Marchini et al., 1988; Lindow et al., 1998). Hence, fetal oxytocin release is not subject to birth stress and even if there is some crossing of the maternal-fetal barrier , fetal oxytocin levels are barely altered. This is in sharp contrast to what has been observed for vasopressin. During vaginal delivery, there is an extremely steep rise of circulating vasopressin which is unparalleled by any changes that may occur during the life span of a human being (Chard et al. The exceptional surge of circulating vasopressin (approximately 100-fold) is observed in infants born by vaginal delivery but not those born by elective cesarean section. For many years, oxytocin has been viewed as the primary hormone edging endocrinology , behavior, and pain in mothers and infants around parturition. Very recent work puts the vasopressin receptor 1A in the focus of peripheral analgesia and pain relief in respect to circulating vasopressin and oxytocin. Here, we present a concise overview on these new findings, will discuss them in context of parturition, and will outline new avenues. Both neuropeptides, oxytocin and vaso-pressin, are synthesized in the hypothalamus from paraventricular and supraoptic nuclei and act either centrally within the brain or peripherally after release by the posterior pituitary gland (Meyer-Lindenberg et al., 2011). In mammals, four receptors have been identified , the oxytocin receptor (OTR) and three receptors that respond primarily to vasopres-sin, vasopressin receptor 1A …