POSSIBLE ROLE OF PLASMA NEUROTENSIN ON GROWTH-HORMONE REGULATION IN NEONATES

Objective: To evaluate secretion of plasma neurotensin (NT) which coul d be involved as a peripheral signal in growth hormone (GH) regulation , NT release was measured during early postnatal life, a period of str iking changes in GH secretion. Methods: Blood samples were collected f rom 19 normal full-term neonates on day 5 and at 3 months of age to ev aluate plasma NT concentrations by radioimmunoassay, serum growth horm one (GH) levels using an immunofluorometric assay, and serum insulin-l ike growth factor-I (IGF-I) values by radioimmunoassay, Results: Five day-old neonates showed significantly higher (p<0.001) mean (+/-SEM) p lasma NT levels (83.55+/-12.07 fmol/ml) compared with those in II prep ubertal children and those in 14 adults who were studied as control su bjects (13.30+/-2.90 and 9.70+/-1.10 fmol/ml, respectively). In 5 day- old neonates we observed significantly higher (p<0.001) serum GH level s (29.53+/-3.40 ng/ml) compared with those in the prepubertal children (1.26+/-0.28 ng/ml), Five day-old neonates showed significantly lower (p<0.001) serum IGF-I concentrations (27.01+/-0.77 ng/ml) than those in the prepubertal children (210+/-25 ng/ml), At 3 months of age, plas ma NT levels (59.37+/-7.47 fmol/ml) and serum GH values (4.40+/-0.60 n g/ml) were significantly decreased (p<0.001), At the 3rd month of life , serum IGF-I levels (44.88+/-4.30 ng/ml) were increased significantly (p<0.001). Conclusions: The human neonate showed very high concentrat ions of NT and GH in comparison with those observed in control subject s, The postnatal rise in IGF-I values is presumed to determine the fal l in serum GH concentrations by stimulating somatostatin secretion. Ne urotensin could be involved as a peripheral signal in the inhibitory m echanisms mediated by release of somatostatin.