Mechanisms of Puerperal Lactation

Abstract

During pregnancy estrogen-medicated augmented prolactin secretion is presumably responsible for a 10-20 fold increase in circulating plasma prolactin; significant differences in basal levels between nursing and nonnursing women persist into the puerperium, reflecting the influence of sucking on maternal plasma prolactin. The release of prolactin is induced via a neurogenic pathway from nipple to hypothalamus and it is proportionate to the length of nursing and to the intensity of the stimulus. There is evidence supporting catecholamine/serotonin control of prolactin release, and the influence of changes in hypothalamic dopamine turnover. The composition of human milk is dependent on various factors; overall, fat composition is 2-5% and protein 9% at 3 weeks and 5% thereafter; milk delivers 20-25 calories per ounce; total fluid and nutritional requirements of the newborn can be met by breastfeeding up to 6 months postpartum. Maternal malnutrition negatively affects lactation; gestational, rather than progestational, food intake influences lactation. Immunity in the newborn is provided also by breast milk through immunoglobulins, thus enhancing the child's protection against internal pathogens. The incidence of gastrointestinal disorders is 1.5/1000 in breastfed infants, and 84.7/1000 in bottle fed infants; the incidence of respiratory infection is .4/1000 and 48/1000, respectively. Prolactin may exert an inhibitory influence on ovarian steroidogenesis, and gonadotropin secretion is disrupted by nipple stimuation; this may account for the low percentage of ovulation among nursing mothers. Lactational amenorrhea has been proven to have great demographic impact; dramatic variations in fertility on the basis of variations in lactational amenorrhea have been described in rural areas of Latin America, Asia, and Africa. Reduction of lactational amenorrhea results not only from changes in sociocultural patterns, but from improved maternal nutrition, often through nutrition programs. When nursing has to be interrupted because of complications full lactation may be restored by oral administration of thyrotropin-releasing hormone. Breastfeeding is possible in 99% of women; the denial of lactation may cause the retention of unwanted weight, which can be compounded by the use of oral contraceptives. Moreover, infantile obesity may stem from the lack of a satiety signal in bottle fed newborns.