Impaired growth hormone response to clonidine in obesity

Clonidine, an imidazoline derivative, is an antihypertensive agent which reduces sympathetic tone by acting in the central nervous system to stimulate alpha-2 adrenoceptors. There is evidence that dopamine and norepinephrine modulate the secretion of GH. Stimulation of GH release is a well-known effect of clonidine in man. Obesity is characterized by an impairment of GH release in response to various stimuli. The aim of this work is to study GH release in response to alpha-2 adrenoceptors stimulation by clonidine in obesity. 12 volunteer obese subjects were studied. 10 normal weight subjects, sex and age matched, were controls. The GH responsiveness was tested with a single oral dose of clonidine (0.15 mg). Blood was sampled for GH radioimmunoassay at 0', 30', 60', 90', 120', 150', 180'. Serum GH basal levels were not significant different in obese subjects compared to controls. In obese subjects, no significant changes occurred in blood GH concentration after clonidine. In normal weight controls, instead, a significant increase of GH values was reached at 90' (P less than 0.05) and at 120' (P less than 0.05) after clonidine. The impairment of GH release after clonidine in obese subjects might be in a reduced serotonin release or in a failure of the hypothalamic-pituitary system to stimulate plasma GH caused by a diminished GH releasing factor stimulatory effect or by an excessive endorphin or somatostatin secretion in obesity.