[Sensitivity of the clonidine and guanfacine tests (alpha-2-adrenergic agonists) as pharmacologic stimulants of growth hormone. Effects on plasma cortisol]

Abstract

Objective: The effects of two pharmacological alpha-2-adrenergic stimuli (clonidine and guanfacine) on GH and cortisol concentrations in the blood in a group of non-growth-hormone-deficient children with short stature was compared.

Patients and methods: Seventeen children (10 males and 7 females) with short stature (height standard deviation score: -2.3 +/- 0.5) were studied. The mean age was 9.4 +/- 2.5 years. The GH response to the clonidine or guanfacine test was positive (> 10 ng/ml) in all subjects.

Results: Oral clonidine test: In 14 cases (82.4%) the GH response was positive (peak value: 17.2 +/- 6.3 ng/ml) and in 3 cases (17.6%) the GH response was negative (false negatives). A significant decrease in plasma cortisol concentration was noted, from a basal level of 17.0 +/- 8.0 to 5.9 +/- 3.8 micrograms/ml at 120 minutes (p < 0.05). Blood pressure decreased significantly (p < 0.05), but without symptoms of hypotension. Somnolence was noted in 16 cases (94.1%). Oral guanfacine test: In 8 cases (47%) the GH response was positive (peak value: 14.2 +/- 3.7 ng/ml) and in 9 cases (52.9%) the GH response was negative (false negatives). A significant decrease in plasma cortisol concentration was noted, from a basal level of 14.2 +/- 6.4 to 7.2 +/- 3.7 at 90 minutes (p < 0.05). Blood pressure did not change and none of the patients had somnolence during the test.

Conclusions: The alpha-2-adrenergic agonists, clonidine and guanfacine, appear to be reliable agents for testing of the growth hormone reserve of the pituitary gland. Plasma cortisol levels decreased significantly with either stimuli. The clonidine test is more sensitive than the guanfacine test and can be recommended as a definitive test for the diagnosis of classical growth hormone deficiency.