3 EFFECT OF GROWTH HORMONE RELEASING FACTOR (GRF) ON PLASMA GROWTH HORMONE (GH) AND PROLACTIN (PRL) LEVELS IN OBESE CHILDREN

Abstract

Obese children have a blunted GH response to conventional pharmacological stimuli. To assess whether this blunted response has a hypothalamic or pituitary origin, the response of plasma GH to a glucagon stimulation test (0.1 mg/kg IM) and to a single IV bolus of 0.5 μg/kg of GRF was studied in 13 obese children [145 ± 7% (SEM) of ideal body weight (IBW)] and compared to that of 19 lean (93 ± 4% of IBW) short children with normal pituitary function (N). Peak GH response to glucagon was lower in obese than in N children (16.0 ± 2.0 vs 29.2 ± 4.5 ng/ml, p < 0.001) as was the GH response to GRF (12.4 ± 2.6 vs 39.2 ± 5.1 ng/ml, p < 0.001); the GH response to GRF tended to be more prolonged in obese than in N children. In neither group was there a correlation between peak GH after GRF and percentage of IBW or age. There were no acute changes in PRL levels after GRF in neither group : a normal decrease was observed between 9 and 11 AM (from 201 ± 48 and 211 ± 49 μU/ml to 146 ± 31 and 108 ± 27 μU/ml in the obese and N group, respectively). Conclusion: obese children have a blunted and prolonged GH response to GRF; this blunting is not correlated with age and is not associated with an acute increase in PRL levels, as seen in children with hypothalamic hypopituitarism (Ped Res 18 : 1216, 1984) and thus probably results from a different mechanism, perhaps at the pituitary level.