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Insulin-like growth factor I receptors on human erythrocytes from normal children: relationship with age
A Acquafredda1, D Murrieta, R M Schimpff
1INSERM U 188, Paris, France.
Insights
Insulin-like growth factor I (IGF I) binding to red blood cells increases with age in children. This suggests that rapid growth in young children is not due to higher IGF I receptor binding.
Area of Science:
- Endocrinology
- Cell Biology
- Pediatrics
Background:
- Insulin-like growth factor I (IGF I) plays a crucial role in growth and development.
- Red blood cells possess receptors for IGF I, but their binding characteristics in children are not well understood.
- Understanding IGF I binding is important for comprehending growth regulation in pediatric populations.
Purpose of the Study:
- To investigate the binding characteristics of IGF I on red blood cells in children and adults.
- To determine the number and affinity of IGF I receptor sites in different age groups.
- To explore the relationship between IGF I binding and age in children.
Main Methods:
- Studied IGF I binding on red blood cells from 13 children (8 months–11 years) and 10 adults.
- Utilized Scatchard analysis to characterize receptor binding kinetics.
- Quantified specific binding, high-affinity receptor sites (Ro1), and low-affinity receptor sites (Ro2) with their respective dissociation constants (K1 and K2).
Main Results:
- Scatchard analysis revealed curvilinear regression, indicating heterogeneous receptor populations.
- Adults showed specific binding of 4.1% with Ro1 = 0.88 (K1 = 10.74 nM-1) and Ro2 = 7.14 (K2 = 0.37 nM-1).
- In children, specific binding ranged from 3% to 6.5%, with significant positive correlation (r = 0.914, P < 0.001) between binding and age.
Conclusions:
- IGF I receptor binding on red blood cells increases significantly with age in children.
- Despite high growth velocity and low IGF I levels in young children, increased receptor binding does not appear to be the underlying mechanism.
- These findings contribute to understanding IGF I's role in pediatric growth and development.
Abstract:
The binding of insulin-like growth factor I (IGF I) on red blood cells has been studied in 13 children aged 8 months to 11 years and in 10 adults. The Scatchard analysis showed a curvilinear regression. In adults, the specific binding was 4.1% of the tracer, the mean number of high affinity receptor sites per cell (Ro1) being 0.88 (K1 = 10.74 nM-1) and the mean number of low affinity receptors sites (Ro2) per cell being 7.14 (K2 = 0.37 nM-1). In children the specific binding ranged from 3 to 6.5%. Ro1 ranged from 0.40 to 3.13 (K1 from 3.48 to 13.61 nM-1). Ro2 ranged from 2.88 to 17.25 (K2 from 0.03 to 0.65 nM-1). The most striking fact was the close positive correlation between the specific binding and the age of children (r = 0.914, P less than 0.001). These data suggest that the high growth velocity of young children, concomitant with the low plasma levels of IGF I which are physiological during infancy and early childhood, does not result from an increased binding of IGF I to cell receptors.