Differential Effects ofl-Dopa and Apomorphine on Glucagon Secretion in Man: Evidence Against Central Dopaminergic Stimulation of Glucagon

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Abstract
In 6 normal subjects, l-dopa (500 mg PO) and apomorphine (0.6 mg sc) increased circulating growth hormone and suppressed prolactin levels in a parallel and quantitatively similar fashion, but only l-dopa induced a rise in plasma glucagon, glucose, and insulin levels. The failure of apomorphine to affect glucagon secretion, despite a substantial effect on growth hormone and prolactin, was also observed in insulin-dependent diabetics known to exhibit A-cell hyperresponsiveness to various stimuli. In view of the highly dissimilar molecular and pharmacologic characteristics of l-dopa and apomorphine, these data do not exclude a local dopaminergic effect of l-dopa at the pancreatic level, but strongly militate against a central dopaminergic pathway for glucagon stimulation.