Leptin serum concentrations in healthy neonates within the first week of life: relation to insulin and growth hormone levels, skinfold thickness, body mass index and weight

BACKGROUND AND AIMS Leptin, the ob gene product, plays a key role in the re gulation of body fat mass and weight in adult life. The mechanisms by which maternal and fetal/neonatal weight are regulated during human pregnancy an d in early postnatal life are poorly understood. High leptin levels are obs erved in women during gestation and in cord blood at term. We have hypothes ized that high leptin levels at term could represent an important feed-back indicator of nutrient supply. Subsequently, leptin could signal adipose ti ssue status during late gestation and during early neonatal life. SUBJECTS AND METHODS 51 healthy newborns were studied. Clinical and auxolog ical data (birth length, weight, and iliac, subscapular, biceps and triceps skinfold thickness) were recorded using a standardized data sheet. Venous cord blood was obtained immediately after birth in all neonates. Subsequent ly, capillary blood was obtained from the heel from some of the newborns wh en blood had to be obtained because of signs or symptoms of particular prob lems such as hypoglycaemia or hyperbilirubinaemia, at the following time po ints: two to four hours after birth in 51 infants, 56-79 h after birth in 4 7 infants and 99-128 h after birth in 23 of the newborns. The ratio between the sexes (girls/ boys) was similar at all time points. The infants that w ere included in the study were subsequently found to be normal and healthy after analysis of the clinical and biochemical data. A specific ultrasensit ive radioimmunoassay was used to measure leptin, while growth hormone and i nsulin were measured using commercially available immunoassays. RESULTS Gestational age was 38-42 weeks, maternal age was 21-42 years. Birt h weights ranged from 2480 to 4400 g. All newborns and mothers were subsequ ently found to be healthy. Leptin levels in Venous cord blood was 0.16-6.80 mu g/l, median 3.47 mu g/l and in capillary blood shortly after birth 0.26 -7.03 mu g/l, median 3.89 mu g/l. 56-79 h after birth leptin levels had fal len dramatically, range 0.02-1.69 mu g/l, median 0.26 mu g/l, while 99-128 h after birth, leptin concentrations in capillary blood (0.05-2.61 mu g/l, median 0.59 mu g/l) had significantly increased when compared to the levels at 56-79 h (P<0.001). There was a significant correlation between leptin l evels in umbilical vein and birth weight of the neonates (r = 0.57, P< 0.03 ). Multistep regression analysis revealed that weight and skinfold thicknes s accounted for approximately 35-70% of the variation of leptin levels. Ins ulin and growth hormone, and glucose and bilirubin however, had no major im pact on leptin levels. CONCLUSION High leptin levels are present in cord blood at birth and in cap illary blood shortly after birth. Since leptin levels in cord blood correla te with birth weight it is tempting to speculate that in the fetus as in la ter life leptin is signalling expansion of fat stores. Most importantly, we now report that leptin levels are high in the fetus but decline rapidly an d dramatically after birth in healthy neonates. This may be important for t he stimulation of feeding behaviour and the acquisition of energy homeostas is in the neonate.