[Hormonal control of lactation]

We studied the mechanism of normal lactation, especially the roles of prolactin (PRL) and oxytocin (OXT) in the initiation of lactation, the lactation in the women complicated with endocrinological disorders, and medical therapies for stimulation and suppression of lactation. The level of serum PRL increases as pregnancy progresses, and reaches to a peak on the day of delivery. Despite high PRL level, milk secretion does not appear during pregnancy, because the sex steroid hormones suppress binding of PRL to the receptor in the mammary gland. The initiation of milk secretion in puerperal women seems to be closely related to an increase in PRL levels induced by adequate suckling. In the mechanism of suckling-induced PRL increase, OXT from posterior pituitary seems to have an important role. Furthermore, the poor response of PRL to suckling was due to insufficient stimulation to the nipples by suckling because the size of nipples were relatively small in these mothers. The other mechanism involved in lactation is suckling-induced OXT secretion. OXT stimulates milk ejection. Anxiety or fear may inhibit the OXT release. We demonstrated that the number of pulsatile release of OXT by nursing was significantly decreased by the psychological stress induced by mental calculation. In the puerperal women with prolactinomas after surgery, the serum PRL level did not increase during pregnancy and milk secretion in puerperium was poor. In the puerperal women with diabetes mellitus, milk secretion was also poor. One of the causes may be related to the low PRL response to suckling stimuli. PRL stimulates milk yield in the mammary gland, but is not commercially available.(ABSTRACT TRUNCATED AT 250 WORDS)