Insulin-like growth factor binding protein-3 proteolysis and growth of athyreotic infants in the first weeks of life.
To gain a better understanding of the growth of athyreotic newborns in the first weeks of life, we evaluated auxological parameters and determined the serum levels of growth hormone (GH), insulin-like growth factor I (IGF-I) and free IGF-I, and IGF-binding protein-3 (IGFBP-3) in 15 hypothyroid infants (10 females) at a mean age of 25 d of life, immediately before the beginning of L-thyroxine therapy, and at 3 and 6 mo of life. Fourteen normal infants (9 females) of the same age were studied as controls. IGFBP-3 proteolytic activity was evaluated in 8 patients and in 8 controls at 25 d and 6 mo of life. There was no significant difference concerning weight and length between the patients and controls at birth, 25 d, 3 and 6 mo of life. The blood GH, IGF-I and IGFBP-3 levels were significantly lower in patients at diagnosis than in controls of the same age (p < 0.01 for all parameters), as well as IGFBP-3 studied by Western blotting. At diagnosis, the patients' free IGF-I level was within the control range, but the free IGF-I percentage of total IGF-I was higher than in the controls (p < 0.01). IGFBP-3 proteolytic activity was found to be greater in the patients (p < 0.01). At 6 mo of life, after therapy, none of these parameters was different from those of the controls.


CONCLUSIONS
Increased IGFBP-3 proteolytic activity in our patients at diagnosis, favouring IGF-I bioavailability, could account for normal free IGF-I levels and in turn for their normal growth pattern during the first weeks of life and before the start of treatment.
Zamboni
G
G
Pediatric Clinic, University of Verona, Italy. gzamboni@borgoroma.univr.it
Antoniazzi
F
F
Tatò
L
L
D000367:Age Factors; D002657:Child Development; D003409:Congenital Hypothyroidism; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000378:metabolism*; D007231:Infant, Newborn; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D008297:Male; D013961:Thyroid Gland / Q000002:abnormalities* / Q000378:metabolism*; D013963:Thyroid Hormones / Q000097:blood
D018972:Insulin-Like Growth Factor Binding Protein 3; D013963:Thyroid Hormones