Effect of hexarelin on growth hormone secretion in Down syndrome

We studied the effect of the maximum response dose of hexarelin (HEX), a potent GH-releasing peptide (His-D,2,methyl,Trp-Ala-Trp-D,Phe-Lys-NH2) (HEX, 2 μg/kg i.v. at 0 min), comparing it with that of GHRH (2 μg/kg i.v. at 0 min) in 15 children with Down syndrome (DS, 10 M and 5 F, 7.5-15 years) and in 15 normal short children (NC, 9 M and 6 F, 8.2-15.5 years). Basal IGF-I levels were similar in DS and NC (313.85 ± 41.19 vs. 247.47 ± 38.63 μg/l). In DS, HEX induced a clear GH response (HEX vs. placebo, AUC 1,900.5 ± 301.7 vs. 116.1 ± 24.8 μg/l/h; p <0.0001) which was higher (p <0.05) than that after GHRH (1,051.0 ± 231.9 μg/l/h). The CH responses to HEX and to GHRH were similar in DS and in NC (AUC 1,936.0 ± 306.5 and 873.8 ± 190.3 μg/l/h). The effect of HEX was higher in pubertal than in prepubertal children (p <0.005). Thus, HEX releases more GH than GHRH also in DS, and the GH response to HEX as well as to GHRH is similar in DS and NC.