In short children, the amount of growth hormone (GH) released after a single dose of a GH‑releasing hormone (like sermorelin) depends on how much GH the body has already been making. Kids who naturally secreted more GH over a full day tended to have a bigger response, but if they had a high GH spike in the three hours right before the test, the response was actually lower.

Endogenous GH secretion was measured every 20 min for 24 h in 36 short children. This was immediately followed by an i.v. injection of GH-releasing hormone (GHRH)(1-29)-NH2 (1 microgram/kg), and GH was estimated every 15 min for the following 2 h. The aim was to determine whether endogenous pulsatile GH secretion had any relation to, or influence on, the GH release induced by GHRH. A high variability was found both in the 24-h GH secretion expressed as area under the curve above the baseline (0-1588 mU/l x 24 h) and the maximal GH response to GHRH (5-296 mU/l), as well as after an arginine-insulin tolerance test (4-59 mU/l). We found a positive correlation (correlation coefficient of Spearman (rs) = 0.49; P less than 0.01) between the GH response to GHRH and the spontaneous GH secretion over a 24-h period, in spite of a negative correlation (rs = -0.80; P less than 0.01) with the GH secretion during the preceding 3 h. We conclude that the GH response to a GHRH test correlates with endogenous GH secretion in short children, and may be helpful in estimating the ability to release GH. It is important, however, to be aware of the influence of the spontaneous GH secretion during the 3 h immediately preceding administration of GHRH.