Serum Prolactin and Respiratory Distress Syndrome in the Newborn

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Abstract
Summary: Prolactin levels were measured in cord blood by radioimmunoassay in 57 premature infants between 26 and 36 weeks of gestation. The level of prolactin was in the range of 20 to 600 ng/ml. Twenty-three of the infants subsequently developed respiratory distress syndrome (RDS). The mean cord prolactin in the infants with RDS was 140 ± 30.7 ng/ml, whereas in the healthy infants it was 276.4 ± 26.4 ng/ml. Cord prolactin levels less than 140 ng/ml were associated with a high incidence of RDS: of 25 infants with prolactin levels of less than 140 ng/ml, 19(76%) had RDS. Of the 34 healthy infants, 28(82%) had prolactin levels above 140 ng/ml. The highest levels (500 ng/ml) of prolactin in the group of infants with RDS were in two infants of diabetic mothers. The data suggest that prolactin might have a role in lung maturation in the human fetus. Speculation: Prolactin is the latest hormone to be added to the list of hormones affecting lung maturation. Three groups have now reported a significant correlation between low cord prolactin levels and respiratory distress syndrome. The relative importance and mode of action of prolactin is unclear at present. Prolactin is present in very high concentration in amniotic fluid, and prolactin receptors are present in lung preparations. Prolactin might act as a direct trigger of lecithin synthesis or in a “chain reaction” along the hypothalamic-pituitary-adrenal axis. It could also be only an indicator of the degree of lung maturation. However, it is rapidly becoming clear that prolactin has a major role not only in lactation but also in fat metabolism, ion transport, and probably lung maturation.