Cholinergic receptor control mechanisms for L-dopa, apomorphine, and clonidine-induced growth hormone secretion in man.

The effect of pirenzepine, an anticholinergic agent, on GH release induced by L-dopa (500 mg po), apomorphine (0.75 mg sc), and clonidine (0.150 mg iv) administration was studied in a group of normal men. Pirenzepine, a cholinergic muscarinic antagonist, completely blocked the GH rise induced by dopamine- and adreno-receptor stimulation. In contrast, the PRL-inhibiting action of L-dopa was not modified by the cholinergic antagonist. The data suggest that acetylcholine and its receptors are important regulators of the neurosecretory mechanisms that control GH secretion in man.