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Quantitation of urinary somatomedin-C in children with normal and abnormal growth
T Quattrin1, C H Albini, R L Vandlen
1Department of Pediatrics, Children's Hospital of Buffalo, New York 14222.
Insights
Urinary somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) levels are lower in children with growth failure and GH deficiency. Measuring urinary Sm-C/IGF-I may provide insights into growth hormone production and action.
Area of Science:
- Pediatric Endocrinology
- Growth Hormone Research
- Biochemical Analysis
Background:
- Somatomedin-C/Insulin-like Growth Factor I (Sm-C/IGF-I) plays a crucial role in childhood growth.
- Assessing Sm-C/IGF-I levels is important for diagnosing growth disorders.
- Urinary excretion of peptides offers a non-invasive method for monitoring their levels.
Purpose of the Study:
- To investigate the renal excretion of Sm-C/IGF-I in children with normal growth, idiopathic growth failure, and GH deficiency.
- To determine the relationship between urinary Sm-C/IGF-I levels and growth hormone (GH) status.
- To explore the potential of urinary Sm-C/IGF-I as a biomarker for GH production and action.
Main Methods:
- Radioimmunoassayable Sm-C/IGF-I was measured in 12-h overnight urine samples from 88 children aged 3-19 years.
- Participants were categorized into healthy children, those with idiopathic growth failure, and GH-deficient subjects.
- GH administration was given to a subset of GH-deficient subjects to assess GH dependency.
Main Results:
- Healthy children exhibited significantly higher urinary Sm-C/IGF-I excretion (28.4 mU/kg) compared to children with growth failure (8.1 mU/kg) or GH deficiency (8.6 mU/kg).
- GH-deficient subjects showed increased urinary Sm-C/IGF-I excretion (from 10.3 to 21.4 mU/kg) after biosynthetic GH administration, confirming GH dependency.
- High-pressure liquid chromatography (HPLC) confirmed the authenticity of urinary Sm-C/IGF-I.
Conclusions:
- Urinary Sm-C/IGF-I excretion is significantly lower in children with growth failure and GH deficiency.
- Renal excretion of Sm-C/IGF-I is dependent on growth hormone levels.
- Quantitation of urinary Sm-C/IGF-I in timed collections may offer valuable information on GH dynamics in pediatric growth assessment.
Abstract:
The renal excretion of radioimmunoassayable somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) was measured in 12-h overnight urine samples obtained from 88 subjects, aged 3-19 yr. The participants included 34 healthy children (group 1), 29 children with idiopathic growth failure and normal GH stimulation tests (group 2), and 25 GH-deficient subjects (group 3). The mean (+/- SEM) urinary Sm-C/IGF-I excretion in group 1 (28.4 +/- 2.1 mU/kg) was significantly greater than that in group 2 (8.1 +/- 1.6 mU/kg) or group 3 (8.6 +/- 1.3 mU/kg). Twenty-two of the 29 subjects in group 2 had urinary Sm-C/IGF-I values less than 8 mU/kg. After the administration of biosynthetic GH to 12 GH-deficient subjects, urinary Sm-C/IGF-I excretion rose from 10.3 +/- 2.3 to 21.4 +/- 4.2 mU/kg within 12 h (P less than 0.05), indicating that renal excretion of Sm-C/IGF-I is GH dependent. One woman with acromegaly had markedly elevated urinary Sm-C/IGF-I excretion (420 mU/kg). The authenticity of urinary Sm-C/IGF-I was confirmed by high pressure liquid chromatography (HPLC). Assay of serial dilutions of urinary Sm-C/IGF-I demonstrated a direct proportionality between concentration and dilution. Although it is not possible to identify whether urinary Sm-C/IGF-I reflects local or generalized synthesis of the peptide, we hypothesize that quantitation of Sm-C/IGF-I in timed urine collections will yield additional information about GH production and action in children with normal and abnormal growth.