Physiology and endocrine changes underlying human lactogenesis II

Lactogenesis stage II, the onset of copious milk secretion, takes place dur ing the first 4 d postpartum in women and involves a carefully programmed s et of changes in milk composition and volume. The evidence is summarized th at progesterone withdrawal at parturition provides the trigger for lactogen esis in the presence of high plasma concentrations of prolactin and adequat e plasma concentrations of cortisol. Although the process is generally robu st, delayed lactogenesis does occur with stressful deliveries and in poorly controlled diabetes. Failure of early removal of colostrum from the breast is associated with high milk sodium and poor prognosis for successful lact ation in many women. We speculate that this problem may result from accumul ation of a substance in the mammary alveolus that inhibits lactogenesis, ev en in the face of appropriate hormonal changes after parturition.