Postnatal changes of leptin levels in full-term and preterm neonates: Their relation to intrauterine growth, gender and testosterone

The present study was carried out to investigate leptin levels in arterial and venous cord serum and in amniotic fluid in full-term infants at birth a nd on the 5th postnatal day to define the relationship of leptin to intraut erine growth rate, gender and early postnatal life. The relation of weight gain to serum leptin levels in male preterm infants was determined measurin g leptin concentration weekly in the first 5 postnatal weeks. Testosterone levels were determined simultaneously to explore a possible relationship be tween leptin and testosterone concentrations. Fifty-three term newborn infants with mean birth weight and gestational age of 3,419 g (range 2,150-4,480) and 38.9 weeks (range 36-41) and 19 preterm male infants (mean birth weight and gestational age were 1,416 g (770-1,80 0) and 30.2 weeks (26-35) were enrolled into the study. Leptin and testoste rone levels were determined by radioimmunoassay. It was demonstrated that s erum leptin levels were markedly elevated in the cord blood without discern ible arteriovenous differences. Cord blood leptin was found to correlate wi th birth weight (r = 0.40, p < 0.002), weight to length ratio (r = 0.40, p < 0.002) and body mass index (r = 0.35, p < 0.005). It was significantly lo wer in boys as opposed to girls (p <0.01) and there was an apparent fall by the 5th postnatal day (p < 0.001). Amniotic fluid contained leptin in much less concentration than cord blood and it proved to be independent of intr auterine growth or gender. Serum leptin concentration in preterm infants at 1 week of age was significantly lower compared with term infants (p <0.002 ) and it increased progressively with age (p < 0.01). An inverse relationsh ip was found between leptin and testosterone level (r = -0.358, p < 0.01) a nd a positive correlation between leptin level and weight/ height ratio (r = 0.674, p < 0.01). It is concluded that leptin derived either from placent a or fetal adipose tissue may be involved in regulating fetal growth and de velopment and it may be related to energy intake, storage and expenditure. In preterm male infants serum leptin concentration increases with postnatal weight and testosterone may suppress leptin synthesis.