Effect of Intravenous Administration of Growth Hormone-Releasing Peptide on Plasma Growth Hormone in Patients with Short Stature

Abstract

Synthetic hexapeptide His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 (GHRP) is known to have remarkable GH releasing activity in a variety of species, especially in men. In this study, we examined the effects of GHRP (1μg/kg BW, iv) on plasma GH in 41 patients with short stature (29 males and 12 females, aged from 8-28 yrs) due to different causes (one after pituitary adenomectomy, nine with perinatal abnormality, two with Turner syndrome, 28 due to unknown causes), and compared the GH responses to GHRP with those to GHRH, L-dopa and insulin. GHRP did not cause any symptoms after the injection. Among 35 patients who had no organic abnormality at the hypothalamo-pituitary region in MRI, plasma GH rises of more than 7μg/L were observed in 34 patients after GHRP injection, 32 patients after GHRH, 21 patients after L-dopa and 24 patients after insulin-hypoglycemia. The mean±SE peaks of plasma GH were 26.6 ± 2.8 μg/L after GHRP, 24.0 ± 3.11/g/L after GHRH, 7.1±1.1 μg/L after L-dopa and 7.5 ± 1.1 μg/L after insulin. Plasma GH peaks appeared within 45 min after GHRP injection, which was earlier than the time of GH peaks in other provocation tests. On the other hand, GHRH slightly but consistently increased plasma GH levels in short patients with pituitary stalk transsection, whereas GHRP did not. Although the mechanism of this finding remains unclear, other factors may be necessary for GHRP to exert its full activity in GH release.In summary, GHRP increased the plasma GH level in patients with short stature more safely, consistently and quickly than other GH stimulants. The GHRP test will therefore be a useful and practical way to examine the GH secretory reserve in short stature.