The effect of both oral and intravenous administration of l-DOPA on growth hormone (GH) secretion was studied in a group of normal volunteers: a significant rise of serum GH levels was observed in both cases.
Growth hormone release in response to insulin hypoglycaemia and to arginine infusion was evaluated in a group of Parkinsonian patients before and after 25 days' treatment with l-DOPA plus a DOPA-decarboxylase inhibitor. In addition, GH response to the above stimuli was studied in a group of patients who had been under treatment for more than 6 months with l-DOPA alone. In untreated Parkinsonian patients, GH response to insulin hypoglycaemia was at the lower limit of normal range while arginine-induced GH release was significantly reduced. Treatment with l-DOPA did not increase GH responses. Some possible interpretations of the results are discussed.
The findings support the possibility that dopamine plays a role in the physiological regulation of GH secretion, as in the case of luteinizing hormone, follicle-stimulating hormone and prolactin release.