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The effect of L-dopa, a precursor of Central-nervous-system catecholamines, on growth-hormone secretion was studied in a group of patients with Parkinson's disease undergoing treatment with the drug. Oral doses (0.5 g) caused a significant rise in plasma growth hormone in patients initially starting therapy or on chronic therapy for as long as 11 months. The rise in plasma growth hormone persisted for 120 minutes after the administration of the drug. The L-dopa-induced rise in plasma growth hormone could not be blocked by either oral or intravenous glucose administration. The data suggest that a dopaminergic mechanism in the median eminence or a norepinephrine-sensitive site in the hypothalamus or limbic system may be involved in the regulation of growth-hormone secretion. Furthermore, patients with Parkinson's disease, on L-dopa therapy, appear to be under the influence of elevated plasma growth hormone for a substantial part of the day.
Boyd et al. (Thu,) studied this question.