EFFECTS OF GROWTH-HORMONE ADMINISTRATION ON NEUROTENSIN RELEASE IN CHILDREN WITH GROWTH DELAY

Neurotensin (NT), a tridecapeptide originally isolated from bovine hyp othalamus, has numerous actions on endocrine functions. Since intraven ous injection of NT in the rat stimulated the release of growth hormon e (GH) among several pituitary hormones, the aim of our study was to i nvestigate in humans the effects of GH injection on NT plasma levels. Plasma samples were obtained from 13 children with growth delay (7 boy s and 6 girls; age range 5 years 1 month - 14 years 1 month; mean +/- SE 10 years 9 months +/- 7 months) to evaluate NT and GH values before treatment and 4, 12 and 24 h after a subcutaneous rhGH injection (0.1 5 IU/kg). Plasma was extracted on a SEP-PAC C18 column and NT was elut ed with propanol. NT concentrations were measured by a specific RIA an d expressed as fmol/ml plasma. GH (ng/ml) and somatomedin C (SMC; U/ml ) were evaluated by RIA using commercial kits. Free fatty acids (FFA; mEq/l) were measured using a colorimetric peroxidase technique. Before GH administration, NT levels were 7.19 +/- 1.01 fmol/ml. A significan t increase in NT values was found 4 h (36.5 +/- 9.62, p < 0.001), 12 h (40.85 +/- 6.64, p < 0.001) and 24 h (19.5 +/- 3.48, p < 0.05) after GH injection. This increase was significantly correlated with the circ ulating GH levels 4 h after GH administration and with the circulating SMC levels 24 h after GH administration. No correlation was found bet ween NT and FFA values. In conclusion, the present data suggest a stim ulatory effect of exogenous GH on NT plasma levels in humans and raise s the hypothesis that circulating levels of NT may be involved in the regulation of GH secretion.