METHIONINE POTENTIATES BOTH BASAL AND GHRH-INDUCED GH SECRETION IN CHILDREN

OBJECTIVE It is widely accepted that arginine is a potent GH secretago gue in man, probably acting via inhibition of hypothalamic somatostati n release. Although many other amino acids are known to stimulate GH s ecretion, their effects and mechanisms of action have not been extensi vely studied in humans. The aim of the present study was to clarify th e effect, if any, of methionine (MET) on GH secretion in children with normal short stature (normal height velocity and IGF-1 > 100 mu g/l). DESIGN We studied the effect of MET (0.2 g/kg intravenously (i.v.) ov er 30 min) on both basal and GHRH (1 mu g/kg i.v. at 0 min)-induced GH secretion (group A) comparing its effect with that of arginine (ARG) at low and classical doses 0.2 and 0.5 g/kg i.v. over 30 min) (groups B and C). The effect of the combined administration of MET and ARG (0. 5 g/kg i.v. over 30 min) (group D) on GH secretion was also studied. P ATIENTS Thirty-four children (20 male and 14 female, age 12.8-14.0 yea rs), divided into four groups. MEASUREMENTS Serum GH was measured in d uplicate by immunoradiometric assay. RESULTS In group A, MET increased basal GH levels (peak, mean +/- SEM 14.6 +/- 2.6 vs 2.6 +/- 0.6 mU/l; P<0.01) and potentiated the GH response to 1 mu g/kg i.v. GHRH (78.0 +/- 17.6 vs 41.6 +/- 9.8 mU/I; P<0.02). In group B, ARG (0.2g/kg) incr eased basal GH levels (16.2 +/- 5.2 vs 2.4 +/- 0.6 mU/I; P<0.03) and p otentiated the GH response to GHRH (119.6 +/- 20.4 vs 48.8 +/- 14.2 mU /I; P<0.01). In group C, ARG (0.5 g/kg) induced a clear GH rise (28.0 +/- 3.8 vs 2.0 +/- 0.6 mU/I; P<0.001) and potentiated the GH response to GHRH (93.4 +/- 10.0 vs 34.2 +/- 4.6 mU/I; P<0.001). The GH response s to MET and ARG alone in groups A and B were similar and lower than t hat to ARG in group C. The GH responses to MET or ARG combined with GH RH in groups A, B and C were similar, In group D MET failed to modify the GH response to 0.5 g/kg i.v. ARG (10.8 +/- 6.4 vs 9.6 +/- 6.0 mU/I ). CONCLUSION Methionine potentiates both basal and GHRH-induced GH se cretion in children as effectively as arginine. As methionine has no i nteraction with arginine, our data suggest that these amino acids act via a common mechanism.