Human growth hormone (hGH) stimulation tests: the sequential exercise and L-dopa procedure

Forty-eight normal volunteers, thirteen subjects with short stature without apparent cause and thirty-one patients with delayed growth clinically highly suggestive of growth hormone deficiency (GHD), with chronological ages of 11.4 +/- 0.4 years (mean +/- SEM), 14.0 +/- 0.7 years and 12.8 +/- 0.8 years; height age of 11.0 +/- 0.4 years, 8.9 +/- 0.7 years and 6.3 +/- 0.4 years and bone age of 10.7 +/- 0.7 years, 9.9 +/- 0.8 years and 7.5 +/- 0.7 years respectively, were tested with provocative tests of human growth hormone (hGH) release-insulin-induced hypoglycaemia, arginine infusion, L-DOPA, exercise and sequential exercise and L-DOPA--in order to identify growth hormone deficiency. In the 'normal' subjects (control plus short stature) the sequential exercise and L-DOPA test induced the greatest peak and integrated secretion rates of plasma hGH (16.5 +- 1.2 ng/ml and 679 +/- 70 ng/ml/120 min respectively) when compared to other tests. This combined stumulus was the only one to which all 'normal' subjects responded: a similar degree of responsiveness has not been earlier described for other hGH-stimuli. The responses observed with all stimuli were significantly lower (P less than 0.001) in GHD group compared to the 'normal subjects'. Emphasis was given to the sequential exercise and L-DOPA test as an innocuous, sensitive and simplified procedure in the evaluation of children with growth retardation.