Seasonal or Gender Effects on Cord Serum Insulin-like Growth factor-I Concentrations in Newborn Infants / 대한주산의학회잡지

ABSTRACT

Possible seasonal differences in serum Insulin-Like Growth Factor-I (IGF-I) concentrations have not been studied in newborn infants. Recently we demonstrated sea- sonal differences in bone mineral content (BMC) in newborn infants lower BMC was present in summer vs. winter-born infants (J Pediatr Gastroenterol Nutr 1992; 15 285). In a second stduy, higher serum osteocalcin, an index of bone formation, and lower BMC were found in summer vs. winter (J Pediatr Gastroenterol Nutr 1994; 19 2207). We speculated that increased serum osteocalcin in summer could be an adaptive response to decreased bone mass. Since growth factors such as IGFs are local regulators of bone formation, we hypothesized that in summer-born infants, serum IGF-I will be higher than in winter, associated with high bone formation activity. Fifty-nine healthy, term appropriate for gestational age (AGA) infants were studied prospectively in winter (Jan-Mar, 29) and in summer (July-Sept., 30). Thirty infants were male, and 29 infants were female. Gestational ages and birth weights were not different by season(in summer, mean+SD, 39.61.1 wk, 3,471360 g,' in winter, 39.31.4 wk, 3,402 392 g). Cord serum IGF-I was measured by radioimmunoassay, modified from Furlanetto et al (1977), after acidification and sep-pack extraction of serum, and osteocalcin concentrations were determined by a kit radio-immunoassay. Cord serum IGF-I concentrations were not different by season of birth(summer vs. winter, 20.11.83 vs. 16.5 1.75 ng/mL, p=0.2). No gender differences were found 18.21.8 vs. 18.2+1.8 ng/ mL in males vs. females. Serum osteocalcin was higher in summer vs. winter-born infants (8.22.3 vs. 4.951.58 ng/mL, p=0.009). BMC was different by season (87.2+ 14.5 vs. 94.1+16.4 mg/cm, p=0.02). Cord serum IGF-I was not related to serum osteocalcin and BMC. We conclude that serum IGF-I concentrations are not different by season or gender, and are not related to bone formation activity and BMC. Thus, IGF -I concentrations in serum are not seasonally regulated, nor associated with an index of bone formation activity.