THE GH-RELEASING EFFECT OF HEXARELIN, A SYNTHETIC HEXAPEPTIDE, IN NEWBORNS IS LOWER THAN IN YOUNG-ADULTS

The aim of the present study was to verify the CH-releasing effect of Hexarelin, a synthetic hexapeptide, in newborns who are known to have GH hypersecretion likely due to hyperactivity of GHRH-secreting neuron s while somatostatinergic activity seems not fully operative, We studi ed in 6 newborns (NB, 2.5 +/- 2.1 days), 12 prepubertal children (PC, 9.8 +/- 0.45 yr) and 12 young adults (YA, 28.2 +/- 0.2yr) the GH respo nse to Hexarelin (HEX, 2 mu g/kg i.v.) compared to that observed after GHRH (1 mu g/kg i.v.) in 6 NB (4.2 +/- 0.4 days), 12 PC (9.9 +/- 0.6 yr) and 12 YA (31.0 +/- 1.3 yr), GH levels were assayed basally and 30 and 60 min after drug administration, In NE, mean (+/- SEM) basal GH levels were higher while IGF-I levels were lower than those recorded i n PC and YA (GH: 34.8 +/- 1.9 vs 2.8 +/- 0.4 vs 1.4 +/- 0.4 mu g/l,p < 0.0006; ICE-I: 36.3 +/- 1.9 vs 152.0 +/- 11.5 vs 175.8 +/- 15.3 mu g/l , p <0.0007); in the last two groups GH and ICE-I levels were similar, The mean delta GB peak after HEX in NE (32.8 +/- 4.7 mu g/l) was simi lar to that in PC (34.6 +/- 4.3 mu g/l) and lower (p <0.01) than that in YA (56.2 +/- 7.4 mu g/l). Delta GH peak after GHRH in NE (60.1 +/- 1.5) was higher than those in PC and YA (20.8 +/- 4.8 and 22.8 +/- 3.4 mu g/l) (p <0.005 and <0.002, respectively), In NE, the GH response t o HEX was lower (p<0.005) than to GHRH while ire PC and YA the somatot rope response to HEX was higher (p <0.03 and 0.0004, respectively) tha n to GHRH, These data demonstrate that the CH-releasing effect of Hexa relin undergoes age-dependent variation being lower in newborns than i n young adults, opposite to that observed after GHRH administration, T he evidence that Hexarelin releases less CH than GHRH in newborns but not in prepubertal children and in young adults makes unlikely the hyp othesis that the CH-releasing effect of this hexapeptide is mediated v ia endogenous GHRH release.