Giving sermolelin continuously under the skin to kids with low growth hormone first spikes their GH levels, but after a few weeks the hormone drops and can even be suppressed, and this drop doesn’t clearly translate into more height growth.

Six children presenting with partial growth hormone (GH) deficiency (mean GH peak in two different tests, 8.0 +/- 1.3 micrograms/l) aged 8-10.3 years (mean, 2.7 +/- 0.9 years) were treated for 6 months by continuous subcutaneous infusion of GH-releasing hormone(1-29)-NH2 (GHRH(1-29)-NH2); 24-hour GH profiles and height velocity were measured. A biphasic effect of GHRH(1-29)-NH2 infusion was observed. After an early substantial increase in the 24-hour integrated concentration of GH, from 1.6 +/- 0.1 to 3.5 +/- 0.7 micrograms/l/minute, a subsequent consistent decrease occurred by 3 months, which was more pronounced after 6 months (mean 24-hour integrated concentration of GH, 1.9 +/- 0.9 micrograms/l/minute). This effect reflects modification of both pulse amplitude and frequency of GH secretion. At the end of the study, one child had complete suppression of GH secretion and two others showed only one peak above 5 micrograms/l during a 24-hour period. No correlation was found between these changes and height velocity. Three children did not grow significantly; the other three children who had a growth response to GHRH(1-29)-NH2 were those with the lowest 24-hour integrated GH concentration at the end of the study. The possible mechanisms involved in this biphasic effect, including GHRH antibodies, changes in somatostatin levels and/or desensitization of pituitary GHRH receptors, have been investigated.