Growth hormone and cortisol secretion after oral clonidine in healthy adults

The purpose of this study was to evaluate oral clonidine for testing growth hormone (GH) responsiveness in healthy adults. Oral clonidine (0.15 mg) produced a satisfactory GH response (greater than 4 ng/ml from basal) in eight out of 10 subjects, which is similar to rates reported after an equivalent intravenous dose. Elevated GH levels at baseline occurred in four out of five female subjects; this did not affect the clonidine-induced GH release. There were no significant differences at any time point in plasma prolactin or cortisol levels following clonidine, compared to placebo controls. Adequate plasma clonidine levels (greater than 0.4 ng/ml) were achieved in all subjects, with corresponding reductions in mean arterial blood pressure, but with only minimal adverse effects. Results from this study indicate that oral clonidine is a reliable method for testing GH responsiveness in adult subjects.