[Determination of growth hormone: comparison between a physiologic stimulus (exercise) and pharmacologic stimuli...

We have compared the release of growth hormone (GH) after exercise (10 minutes pedaling on a fixed bicycle with ergometer), and two pharmacological alpha-adrenergic stimuli: clonidine (CL) or guanfacine (GU); in 36 prepuberal children whose height was below the third percentile. The tests were carried out in basal conditions, randomized and with a minimum interval of seven days between them. Blood GH was determined from cannulated antecubital veins. The results show a positive response (GH greater than 7 ng/ml) in 65.7% of cases after exercise, in 74.2% after CL and 71% after GU. The significant secondary effects observed after CL administration were sleepiness and decrease of arterial pressure. It is concluded that exercise is a useful test for assessing a possible deficiency of GH, and lacks significant side effects and that the diagnostic value of GU is similar to that of CL.