The glucagon infusion test and growth hormone secretion

The glucagon test in the diagnosis of growth hormone deficiency in children with short stature younger than 6 years

CONTEXT

Few studies have addressed the diagnostic role of the glucagon test in children with suspected GH deficiency (GHD).

OBJECTIVE

The objective of the study was to investigate the diagnostic value of the glucagon test as an alternative test to insulin tolerance test (ITT) and arginine in GHD children younger than 6 yr.

DESIGN AND SETTING

This study was conducted in two pediatric endocrinology centers.

PATIENTS AND METHODS

Forty-eight children (median age 4.2 yr, median height -3.0 sd score) with GHD confirmed by a peak GH to ITT and arginine less than 10 microg/liter (median 4.7 and 3.4 microg/liter, respectively) underwent a glucagon stimulation test. Magnetic resonance imaging showed normal hypothalamic-pituitary anatomy in 24 children, isolated anterior pituitary hypoplasia in seven, and structural hypothalamic-pituitary abnormalities in 17.

RESULTS

Median GH peak response to glucagon (13.5 microg/liter) was significantly higher than that observed after ITT and arginine (P < 0.0001). GH peak after glucagon was less than 10 microg/liter in 20 subjects (group 1) and greater than 10 microg/liter in 28 subjects (group 2) without significant clinical or biochemical differences between the two groups. Median GH peak after glucagon was similar between patients with multiple pituitary hormone deficiency and those with isolated GHD and between subjects with and without structural hypothalamic-pituitary abnormalities. The magnitude of the GH peak after glucagon was negatively correlated to age at diagnosis (rho = -0.636, P < 0.0001).

CONCLUSIONS

This study shows that glucagon has an effective GH-releasing activity and can be used to evaluate somatotroph function in young children with short stature. Normative data for this test in young children need to be established before its use in clinical practice.

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.

Rational use of the laboratory for childhood and adult growth hormone deficiency

No laboratory test has sufficient diagnostic sensitivity and specificity to serve as a gold standard for the diagnosis for GHD: therefore, test results must be interpreted after assessment of risk for GHD is determined on clinical grounds. Growth data are particularly crucial for diagnosis of childhood GHD;history of known pituitary damage and presence or absence of other pituitary hormone deficiencies are the critical elements for the diagnosis of adult GHD. New reference preparations are available for GH and IGF-I and should greatly aid interassay comparisons when the preparations are universally adopted.GH stimulation testing remains a key part of the diagnosis of adult GHD, but is currently being de-emphasized for the diagnosis of pediatric GHD. Better interassay comparative data and organized clinical collaboration between clinicians and test manufacturers/laboratories to set rational clinical diagnostic cutoffs would improve greatly the clinical usefulness of GH stimulation testing. The availability of statistically sound age- and sex-related normative data for IGF-I and IGFBP3 make these key tests for the diagnosis of childhood GHD. Although IGF-I may not be a perfect test for the diagnosis of adult GHD, it may be sufficiently informative in many cases to warrant using it ona routine basis. IGF-I also has a role in monitoring the safety of adult patients who are on GH treatment; studies are underway to determine if IGF-I may be useful in the future for optimization of GH dosaging.

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

Thirty-seven children and adolescents of several diagnostic entitites (constitutional growth retardation, diabetes mellitus and pituitary insufficiency) were tested with an i.v. bolus injection of glucagon for plasma human growth hormone (HGH) response. Most of the subjects were also tested for the same purpose by the arginine stimulation test, and the data were compared. It was found that i.v. glucagon is a potent stimulus of human growth hormone release. The HGH is released in two peaks, the first one occuring within 30 min, most probably by a direct effect. The second peak occurs after 120 min, most probably as a secondary effect caused by the drop in blood glucose after its initial rise, which is induced by glucagon. The peak concentrations of HGH induced by glucagon, were very similar to those provoked by i.v. arginine in the same subjects.

Liver dysfunction and histologic abnormalities in neonatal hypopituitarism

Pituitary aplasia or hypoplasia occurs in anencephalic and normocephalic infants. Two infants with hypopituitarism are described; in each the diagnosis was made clinically. The infants had frank clinical and histologic evidence of the neonatal hepatitis syndrome. There may be more than a chance relationship between the clinicopathologic findings of neonatal hypopituitarism and hepatitis.