The variability of growth hormone(GH) response to growth hormone-releasing hormone(GHRH) according to the intrinsic growth hormone secretory rhythm in children with normal growth hormone reserve

ABSTRACT

The diagnostic value of GHRH in assessing GH secretion in biochemical GH sufficient short children was examined. GHRH (1microgram/kg i.v bolus) was given to three groups (upslope, trough, downslope) arbitrarily classified according to the basal pulsatile GH secretory pattern before GHRH administration. Cmax following GHRH administration were variable and overlapping. Two children in downslope group, three children in trough group, and one child in upslope group showed subnormal GH responses to GHRH administration despite of normal GH response to more than two classical GH provocative tests (Fig.1). The time of maximal GH response after GHRH administration (Tmax) in upslope group was significantly faster than those in other two groups (Fig.2). There was a highly significant correlation between AUC and Cmax (p<0.001) after GHRH administration (Fig.3) which suggests that AUC or Cmax can be used for parameters of GH response to GHRH each other. The AUC and Cmax after GHRH administration between three groups were significantly different (2764+/-579.1ng/ml min, 52.6 ng/ml, respectively in upslope group; 1645+/-383.9ng/ml min, 37.7+/-9.4ng/ml, respectively in downslope group; 1098+/-150.2ng/ml min, 26.3+/-4.5ng/ml, respectively in trough group)(p<0.005) (Fig.4, Table 1). In conclusion, GH responses to GHRH adminstration could be variable according to the basal GH secretory rhythm. Therefore, we should be cautious in interpreting the GH response to GHRH to evaluate the GH secretory capacity because subnormal GH response to GHRH administration could be observed even if normal GH response to classical GH provocative tests. In addition, the classification of these arbitary three groups (upslope, trough, and downslope) is remained to defined so as to promote the diagnostic value of GHRH in GH deficiency.