GH-releasing Hormone Stimulation Research Articles

Negative correlation between peripheral plasma somatostatin levels and GH responses to GH-RH stimulation tests in children.

On forty-six fasting and resting children, aged 5-17 years, with short stature (below -2 SD) a growth hormone releasing hormone (GH-RH) stimulation test (2 micrograms/kg iv bolus, Sanofi) was performed. Twenty-two children were prepubertal, of which, 13 had a constitutional short stature (CSS), nine an idiopathic growth hormone deficiency (IGHD). Twenty-four subjects were pubertal, at the stage II or III of Tanner. Among them, six had a constitutional short stature (CSS) and 18 an idiopathic delayed puberty (IDP). Blood samples were taken for determination of plasma somatostatin-like immunoreactivity (SLI) in chilled test tubes containing EDTA + aprotinin. Plasma SLI levels were measured after extraction and concentration on C18 Sep Pack columns by radioimmunoassay using an antibody against 1-14 somatostatin. The sensitivity of this assay is around 3 pg/ml. After GH-RH stimulation the peak of GH (mean +/- SEM) was in prepubertal subjects: 25.3 +/- 9.1 micrograms/l in CSS, and 18.6 +/- 10.3 micrograms/l in IGHD. In pubertal subjects GH peaks were 17.6 +/- 8.4 micrograms/l in CSS and 15.6 +/- 3.8 micrograms/l in children with IDP. No significant differences was found between basal plasma SLI levels in the four groups of subjects, being respectively (mean +/- SEM) 11.9 +/- 1.8 pg/ml in prepubertal subjects with CSS, 9.6 +/- 2.6 pg/ml in IGHD, 7.6 +/- 1.7 pg/ml in pubertal children with CSS and 6.6 +/- 1.5 pg/ml in children with IDP.(ABSTRACT TRUNCATED AT 250 WORDS)

Dual effects of growth hormone (GH)-releasing hormone infusion in normal men: somatotroph desensitization and increase in releasable GH.

Continuous infusion of human GH-releasing hormone (GHRH) stimulates GH secretion in normal subjects, but a single supramaximal iv dose of GHRH thereafter elicits a diminished serum GH response compared to that after a saline infusion; the response to the single dose challenge is inversely related to the dose of GHRH previously infused. To determine if this attenuated GH response is a result of depletion of available GH or desensitization of the somatotroph, a 6-h infusion of saline or GHRH (10 ng/kg . min) was administered to 10 normal men, and an iv bolus dose of either GHRH (3.3 micrograms/kg) or regular insulin (0.15 U/kg) was given after 5.5 h of infusion. On both days of GHRH infusion, there was significant stimulation of GH secretion compared to that after saline infusion. The GH response to the supramaximal dose of GHRH was greater after saline infusion than after GHRH infusion, and the GH response to insulin-induced hypoglycemia was significantly greater after GHRH infusion compared with the responses on the other 3 study days. The greatest GH secretion occurred during GHRH infusion followed by insulin administration; therefore, pituitary reserve was not decreased by prior exposure to GHRH. These studies suggest that somatotrophs become partially refractory to GHRH stimulation over time, but remain responsive to an alternate stimulus of GH secretion. We suggest that the hypoglycemia-induced GH response occurs via a reduction in hypothalamic somatostatin secretion, and the attenuated GH response to the supramaximal GHRH dose after GHRH infusion probably represents either partial desensitization or down-regulation of the GHRH receptor.