Urinary insulin-like growth factor-II excretion in healthy infants and children with normal and abnormal growth

The output of urinary IGF-II was measured by RIA in 12-h overnight urine samples obtained from 22 preterm and 15 full-term infants, 40 normal children, 18 children with growth hormone (GH) deficiency, and 25 patients with idiopathic short stature. GH deficiency was defined as a peak to GH provocative tests <9.9 µg/L during two provocative tests. The authenticity of urinary IGF-II was confirmed by size exclusion chromatography. Statistical analysis was performed by one-way analysis of variance using the Student Neuman-Keuls test to detect inter-group differences at the level of p < 0.05. The preterm and full-term infants excreted significantly higher amounts of urinary IGF-II (18.4 ± 1.7 and 5.7 ± 1.0 pmol/kg, respectively) compared with normal children (2.4 ± 0.25 pmol/ kg; p < 0.001). The output of urinary IGF-II in preterm infants was greater than that observed in full-term infants (F = 84.7, p < 0.001). The control children excreted significantly more IGF-II (2.4 ± 0.2 pmol/kg) than children with GH deficiency (0.9 ±0.1 pmol/kg) or idiopathic short stature (1.0 ± 0.1 pmol/kg; F= 13.5; p < 0.001). Analysis of urinary IGF-II excretion based on creatinine output yielded similar results. Data on urinary IGF-I and GH previously published were correlated and compared with the excretion pattern of urinary IGF-II. Urinary GH correlates with urinary IGF-II in groups 3, 4, and 5 (0.58 and 0.46 per body weight and nmol of creatinine, respectively; p < 0.01), as well as in the preterm and full-term infants (0.51, p < 0.01; 0.54, p < 0.01) when the data were standardized for kg of body weight and nmol of creatinine, respectively. Children with GH deficiency excrete significantly less IGF-II compared with control subjects. This pattern is similar to that of urinary IGF-I. The highest urinary IGF-II output is observed in preterm infants, possibly reflecting a period of persistent elevation of IGF-II secondary to the young gestational age of these infants.