About the effects of glucagon on growth hormone release

Glucagon administration elicits blunted GH but exaggerated ACTH response in obesity

Reduction in both spontaneous and stimulated GH secretion in obesity has been clearly demonstrated. Mild hyperactivity of hypothalamus-pituitary-adrenal (HPA) axis has been also reported. Glucagon, at least after im administration, induces clear increase in either GH or ACTH and F levels but its effect on somatotroph and corticotroph secretion in obesity has never been studied. In 7 patients with abdominal obesity (OB, aged 24-42 yr, BMI: 29.1-43.9 kg/m2, waist/hip ratio [WHR]: 0.86-1.00) we studied the GH, ACTH and F responses to the im administration of glucagon (0.017 mg/kg at 0 min). The results in OB were compared with those in a group of 6 age-matched controls normal subjects (Ns aged 26-32 yr, BMI 19.7-22.5 kg/m2). In Ns glucagon administration induced clear increase in GH (peak vs baseline, mean+/-SE: 11.6+/-3.4 vs 3.3+/-0.7 microg/l, p<0.02), and ACTH (52.9+/-15.2 vs 19.0+/-1.5 pg/ml, p<0.02) levels which peaked at +150 and +165 min, respectively. Increase in F levels (222.3+/-23.8 vs 158.3+/-7.0 ng/ml, p<0.05) was also recorded but peaked at +180 min. In OB glucagon administration induced GH response (7.4+/-2.3 vs 0.8+/-0.6 microg/l) lower (p<0.05) than that recorded in Ns; when the GH responses were evaluated by co-variance analysis, a significant difference between the 2 groups was recorded in term of peaks but not of AUCs. On the other hand, the ACTH response to glucagon in OB was higher than that in Ns (11452.6+/-2447.7 vs 4892.2+/-719.4 pg/ml x min, p<0.05). The F response to glucagon in OB and Ns was, however, similar (24057.9+/-4109.1 vs 29835.9+/-1566.0 ng/ml x min). In conclusion, this study demonstrates that in obese patients the im administration of glucagon elicits blunted GH response but exaggerated ACTH increase which is uncoupled with the adrenal response. These findings agree with the existence of concomitant GH insufficiency and altered corticotroph function in obesity.

Glucagon is an ACTH secretagogue as effective as hCRH after intramuscolar administration while it is ineffective when given intravenously in normal subjects

It is widely accepted that glucagon stimulates GH, ACTH and cortisol release in humans, though the mechanisms underlying these effects are unclear. Aim of the present study was to evaluate the stimulatory effect of intramuscolar (i.m.) and intravenous (i.v.) glucagon (GLU) administration on ACTH, cortisol (F) and GH release in normal adult subjects and to compare its effect on hypothalamo-pituitary adrenal (HPA) axis with that of hCRH. To this goal, in 6 normal young women (26-32 yrs, 50-58 kg) we studied the ACTH and F responses to either i.m. or i.v. GLU (1 mg, approximately 0.017 mg/kg in subjects of 54.1 +/- 1.6 kg) administration as well as to i.v. hCRH (2.0 micrograms/kg) or placebo administration. The GH and glucose variations after GLU administration were also studied. I.v. GLU did not modify the spontaneous decrease of ACTH and cortisol levels observed after placebo. Conversely, i.m. GLU elicited clear-cut ACTH and F responses (peak vs baseline, mean +/- SEM: 53.0 +/- 15.2 vs 19.0 +/- 1.5 pg/ml, p < 0.05 and 222.3 +/- 23.8 vs 158.3 +/- 7.0 micrograms/l, p < 0.05) which were higher than those recorded after hCRH (28.1 +/- 4.6 vs 17.4 +/- 3.1 pg/ml, p < 0.02 and 182.7 +/- 22.8 vs 114.8 +/- 12.3 micrograms/l p < 0.02), though this difference did not attain statistical significance. Also GH rise was recorded after i.m. but not after i.v. GLU administration (11.6 +/- 3.4 vs 3.3 +/- 0.7 micrograms/l, p < 0.05). Thirty min after both i.v. and i.m. GLU administration glucose levels showed a similar increase followed by similar decrease. The intramuscular administration of GLU induced negligible side-effects in some subject (mild and transient nausea) which, on the contrary, were clear in all subjects after its intravenous administration (nausea, vomiting, tachycardia). In conclusion, glucagon "per se" is not an ACTH, cortisol and GH secretagogue. After intramuscular administration glucagon is a stimulus of HPA axis at least as effective as hCRH. The mechanisms underlying the ACTH, cortisol and GH responses to i.m. glucagon unlikely include glucose variations or stress.