The Effect of a Single Dose ofl-Dopa on Pituitary Hormones in Acromegaly, Obesity and in Normal Subjects

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Abstract
We have evaluated the potential stimulatory effects of a single 1.0 g dose of l-dopa; on pituitary hormones in 14 acromegalic, 4 obese and 14 normal subjects. l-dopa; was administered orally in the morning to fasting subjects and blood samples were obtained every 30 min up to 180 min throughout the procedure. Nausea and/or vomiting and an occasional mild headache occurred in some subjects in each group. No significant change in mean serum TSH, LH, FSH, plasma cortisol or serum glucose was observed. However, following the administration of l-dopa; to 9 of 14 normal subjects, mean GH concentrations increased to a peak of 38.5 ng/ml. These peak responses ranged from 12 to 80 ng/ml and occurred between 30 to 120 min following l-dopa;. Five of 14 normal subjects were “poor responders” to l-dopa; with GH elevations of less than 5.0 ng/ml. There was no rise in GH in 14 acromegalic patients receiving l-dopa; and 5 of 14 showed a paradoxical decrease in GH concentration. GH concentration rose in 3 of 12 acromegalics following intravenous insulin, despite minimum hypoglycemia and a previously absent l-dopa; response. Mean plasma cortisol was generally unchanged in acromegalic patients following l-dopa; and insulin induced hypoglycemia, although a few responded to both procedures. Obese patients showed no significant change in GH concentration following a single dose of l-dopa;. A single 1.0 g dose of l-dopa; did not consistently stimulate GH in normal subjects, in obese or acromegalic patients, nor did it appear to stimulate other pituitary hormones. However, l-dopa; appears promising as an investigational tool of the hypothalamicpituitary axis.

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