Growth hormone response to L-dopa and clonidine in autistic children

Studies have shown abnormal pituitary hormone responses to neuroendocrine agonists in autistic subjects. Two probes (clonidine and L-Dopa) were used to investigate neuroendocrine responses through changes in growth hormone levels. Seven medication-free autistic subjects (ages 6.6 to 19.1) were evaluated and compared to 14 normal controls. Growth hormone was collected at 30-min intervals during the entire study. Clonidine was administered first (dose: 0.15 mgm2), and samples were collected for 180 min. L-Dopa was then administered (dose: 250 mg for subjects less than 70 lb and 500 mg for subjects greater than 70 lb), and samples were collected for 120 min. There was no difference in the amplitude of the clonidine or L-Dopa peak growth hormone responses in the control versus the autistic subjects. In the autistic subjects, the L-Dopa-stimulated growth hormone peak was delayed and the clonidine growth hormone peak was premature. A statistical difference with the control subjects was found when consideration was given to both the premature response of growth hormone to clonidine and the delayed response to L-Dopa (p = .01, Fisher's Exact Test). These findings suggest possible abnormalities of both dopaminergic and noradrenergic neurotransmission in subjects with autism.