Comparative HGH response to i.v. glucagon and i.v. arginine stimulation tests in children and adolescents

Prolactin response to growth hormone stimulation tests

BACKGROUND

Despite many similarities between the structure, receptors, proliferative and growth promoting actions, the relationship between Prolactin (PRL) and Growth Hormone (GH) in clinical conditions has received little attention.

OBJECTIVE

To determine the PRL response to GH stimulation tests.

SUBJECTS

Prepubertal and early pubertal boys (n = 581) and girls (n = 502) with idiopathic, non-syndromatic short stature.

DESIGN

Data was retrieved from the computerized records of the Endocrine Laboratory, Schneider Children's Medical Center. Peak GH and PRL levels during GH stimulation tests with glucagon (Gluc), Clonidine (Clon) and Clonidine with arginine (Clon+Arg), were compared. Both PRL and GH were determined by radioimmunoassay.

RESULTS

Whereas Gluc stimulated both GH and PRL to similar levels, Clon alone or combined with Arg suppressed the PRL secretion (p < 0.0001). It is also evident that in both boys and girls Clon alone and Clon±Arg are superior to Gluc in GH stimulation. The higher GH levels during Clon+Arg than with Clon alone are attributed to the pubertal stage.

CONCLUSION

This study provides further information on the Prolactin-Growth hormone relationship in children.

Relationship between GH response and glycemic fluctuations in the glucagon stimulation test

OBJECTIVE

Verifying the association between glycemic fluctuation and GH response in the glucagon stimulation test. Basal evaluation of growth hormone (GH) has poor diagnostic accuracy due to its pulsatile secretion. GH-stimulation tests are used for an adequate evaluation of somatotrophic axis. Various stimuli can be employed, among them glucagon, which has an elusive mechanism of action. Since hypoglycemia reportedly occurs during the test, investigation of its role as a stimulus to GH release is granted.

DESIGN

Retrospective analysis of glucagon-stimulated GH tests performed in 128 children (36.7% female; age 12.4+3.3 years), at Fleury Functional Tests Facility from July 2000 to 2006. GH and blood glucose (BG) curves, IGF-1, and IGFBP-3 have been assessed. Positive GH response was defined by a peak GH value >or=3.3 microg/L. Normal IGF-1 levels were defined as those between 2.5th and 97.5th percentiles for age and gender.

RESULTS

Hypoglycemia under 2.2 mmol/L did not occur during the test. BG decrease occurred with lower magnitude and was not associated to GH response. Comparison between patients with negative and positive GH response showed, respectively, BG nadir 3.74 vs. 3.62 mmol/L, glucose AUC 23.3 vs. 22.4, and glycemic decrease (below 3.3 mmol/L) 19% vs. 35.5% (with P non-significant for all comparisons).

CONCLUSION

Hypoglycemia was not seen after glucagon stimulation and decrease in BG occurred above levels physiologically expected to stimulate GH release, being apparently not associated to GH response.

Ghrelin Is Suppressed by Glucagon and Does Not Mediate Glucagon-Related Growth Hormone Release

BACKGROUND

Glucagon stimulation is routinely used as a provocative test to assess growth hormone (GH) sufficiency in pediatrics. Ghrelin also markedly stimulates GH secretion. Because glucagon stimulates the promoter of the ghrelin gene in vitro as well as ghrelin secretion by the perfused rat stomach, we sought to determine whether ghrelin mediates glucagon-induced GH secretion.

METHODS

We compared ghrelin, GH, insulin and glucose responses following administration of 0.03 mg/kg intravenously (iv; max. 1 mg) and 0.1 mg/kg intramuscularly (im; max. 2 mg) of glucagon in two groups (n = 10-11/group) of GH-sufficient children. We also measured ghrelin before and 6 min after iv administration of 1 mg glucagon in 21 adult subjects.

RESULTS

In children, glucagon caused a 26% decrease in ghrelin and a 72% increase in glucose concentrations that were independent of the dose or administration route of glucagon. In contrast, the insulin response was 2-3 times higher following administration of 0.1 mg/kg im compared to 0.03 mg/kg of glucagon iv. There was a significant correlation between the maximum decrease in ghrelin and increases in glucose (p = 0.03) but not in insulin. There was a significant correlation between ghrelin and GH area under the curve after controlling for the dose of glucagon (p = 0.03) but not for the maximum increase in glucose.In normal adults, glucagon administration caused a 7% decrease in ghrelin concentrations after 6 min (p = 0.0002).

CONCLUSION

Ghrelin does not play a causal role in the GH response to pharmacological glucagon administration, which suppresses ghrelin levels starting a few minutes after injection.