Inhibitory Effect of Dopaminergic Stimulation on GH Release in Acromegaly

Abstract

In 15 out of 19 acromegalic patients, oral administration of l-dopa (500 mg) determinated a conspicuous fall in GH plasma levels. In 8 out of these 15 patients the inhibitory effect was constantly observed when the test was repeated; apomorphine administrtion (0.75 mg sc) was also followed by a significant fall (p < 0.01 at 30′–45′; p < 0.05 at 60′) of plasma levels of GH. These results are consistent with the hypothesis that the inhibitory effect of l-dopa is mediated by an activation of dopaminergic receptors at the hypothalamic or at the pituitary level. Chronic administration of l-dopa does not achieve any stable reduction of plasma GH levels because of the shortness of the inhibitory effect. l-dopa, associated with an inhibitor of decarboxylase, does not give better results.