Hypothalamic norepinephrine: concentration and metabolism during pregnancy and lactation in the rat

Both norepinephrine (NE) and its major metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), were assayed in rat hypothalamus during selected stages of pregnancy and lactation. No changes were observed in the concentration of either NE or MHPG at 5, 15 or 21 days' gestation. However, with 8-15 h after parturition, the concentration of NE decreased sharply while that of MHPG showed a correspondingly sharp increase. The possible significance of such change in hypothalamic catecholamine activity was considered in relation to parturition, postpartum estrus and onset of maternal behavior.