Sequential administration of arginine and arginine plus GHRH to test somatotroph function in short children

The hormonal diagnosis of GH deficiency in childhood's conventionally based on the GH response to at least two provocative stimuli. Among these, argin ine (ARG) has long been considered a classical, centrally mediated stimulus of GH secretion. ARG is also able to potentiate the GH response to GHRH, l ikely inhibiting hypothalamic somatostatin; this combined test is one of th e most potent to explore the maximal secretory capacity of somatotroph cell s. Based on these premises, we verified whether the sequential administrati on of ARG and ARG+GHRH could be feasible as single step provocative test to evaluate the GH releasable pool in short children. To this goal, 48 normal short children (35 M and 13 F, 12.0+/-0.4 yr, PS 1: 255 II-IV: 23) underwe nt a test with ARG (0.5 g/kg iv from 0 to +30 min) followed by a coadminist ration of ARG (from +120 to 150 min) plus GHRH (1 mu g/kg iv at +120 min). ARG alone elicited a clear GH response (mean peak vs baseline: 12.1+/-1.7 v s 2.0+/-0.4 mu g/l, p<0.001, C-max range 12-51.0 mu g/l). Following this GH rise, the hormonal levels at +120 min approached to baseline levels (4.2+/ -0.8 mu g/l) but then showed marked response to the coadministration of ARG +GHRH. The GH peak following ARG+GHRH (mean peak: 47.8+/-3.3 mu g/l, p<0.00 1; C-max 22.4-150.0 mu g/l) was clearly higher (p<0.001) than that recorded after ARG alone. The GH responses to both ARG and ARG+GHRH were independen t of gender, puberty, height velocity, body mass index (BMI) and IGF-I leve ls. Nine normal short children (16%) had GH peaks lower than 7 mu g/l after ARG alone, while none showed GH peak below 20 mu g/l after ARG+GHRH. Thus, ARG alone is a good stimulus of GH secretion but false positive responses frequently occur in normal short children. ARG+GHRH is a more potent stimul us giving no false positive responses even after previous challenge with AR G alone. Testing with sequential administration of ARG and ARG+GHRH may all ow the single step evaluation of the somatotroph response to central and pi tuitary stimuli in short children. (J. Endocrinol. Invest. 23: 97-101, 2000 ) (C)2000, Editrice Kurtis.