Comparison of single and combined tests for the evaluation of plasma growth hormone secretion in normal short children.
Growth hormone (GH) response to provocative tests was compared in normal short children. Seven of 23 children failed to respond to insulin hypoglycemia. Using insulin hypoglycemia followed by L-dopa only 2 of 23 children did not respond and giving bromocriptine combined with insulin hypoglycemia only 1 of 8 children failed to respond. All children submitted to propranolol followed by exercise (n = 14) and to bromocriptine followed by exercise (n = 6) responded with a satisfactory increase in plasma GH levels. The increase elicited by propranolol and exercise was higher than that induced by insulin hypoglycemia alone (p less than 0.005), exercise alone (p less than 0.05) or L-dopa after insulin hypoglycemia (p less than 0.01). The rise of GH induced by bromocriptine and exercise was higher than that obtained with insulin hypoglycemia alone (p less than 0.05). This study suggests that both adrenergic and dopaminergic mechanisms are involved in exercise induced GH release and confirms that combined tests are more useful than a single test to evaluate GH secretion.