Human growth hormone and dopaminergic drugs, with special reference to deprenyl (selegiline): a summary of studies on volunteers.

The tubero-infundibular dopaminergic tract of the hypothalamus has a stimulatory effect on growth hormone (GH) secretion. In healthy volunteers levodopa, through the released dopamine and direct dopamine receptor agonists, therefore induces transient GH secretion. The indirect effect of levodopa at the presynaptic level can be modulated by inhibitory GABAergic drugs and by the potentiating deprenyl, for example. The GH response to direct postsynaptic dopamine receptor agonists like apomorphine is unaffected by these modulators. Below the dopamine level, the inhibitory effect of somatostatin and the negative feedback of the GH itself come into play. These regulatory mechanisms place limitations on dopamine-GH studies in man.