GH secretion in Prader-Labhard-Willi syndrome: Somatotrope responsiveness to GHRH is enhanced by arginine but not by pyridostigmine

Low somatotrope responsiveness to secretagogues has been reported in patients affected by Prader-Labhard-Willi Syndrome (PLWS). In normal subjects, GH response to GHRH is known to be greatly potentiated to the same extent by pyridostigmine (PD) or arginine (ARG) which probably act via inhibition of hypothalamic somatostatin release. To clarify somatotrope responsiveness in 7 PLWS patients, we studied GH response to GHRH alone and to GHRH combined with PD or ARG. Eight normal short children were studied as controls (NC). GH response to GHRH in PLWS was lower than in NC (AUC: 615 ± 205 μgf/l·h, vs 1271 ± 333 μg/l·h, p < 0.02). In NC, the GHRH-induced CH rise was potentiated to the same extent by PD or ARG. In contrast, in PLWS PD failed to increase the GH response to GHRH (AUC: 615 ± 205 μg/l·h vs 621 ± 176 μg/l·h, n.s.) which was enhanced by ARG (AUC: 615 ± 205 μg/l·h vs 1633 ± 425 μg/l·h, p < 0.02). However, the GH response to GHRH + ARG in PLWS was lower than in NC. In conclusion, our results demonstrate that in PLWS the low somatotrope responsiveness to GHRH is not enhanced by cholinergic potentiation while it is increased by arginine.