Different GH responsiveness to repeated GHRH administration in normal children and adults

It has been previously reported that repeated GHRH administration leads to a reduction in growth hormone responses in adults. In order to verify if this regulatory mechanism is also operating in children, we compared GH secretory responses to repeated GHRH in normal children and adults. The administration of the first GHRH bolus caused a marked GH rise (expressed as net incremental area under the curve, nAUC +/- SE) both in children (GH nAUC: 1184 +/- 216 ng/ml/h) and in adults (GH nAUC: 701.2 +/- 90 ng/ml/h). The second GHRH bolus induced a different pattern of GH secretion in the two groups. In children the peptide determined a clear GH rise (GH nAUC: 518 +/- 147 ng/ml/h), while in adults the second GHRH injection was uneffective (GH nAUC: 21 +/- 20 ng/ml/h). These preliminary results indicate that in children repeated GHRH administration does not induce refractoriness to GHRH action, suggesting different regulatory mechanism of GH secretion in normal children and adults.