A study of pineal-prolactin interaction: prolactin response to an acute melatonin injection in patients with hyperprolactinemia.

Several studies demonstrated that the pineal gland plays a regulatory role in PRL secretion. At present, however, there are few clinical data only about the pineal function in PRL secretion disorders. To further clarify which is the pineal importance in the dysfunctions of PRL release, we have evaluated the effect of an acute injection of the pineal hormone melatonin in 19 patients with hyperprolactinemia, 8 of whom had idiopathic hyperprolactinemia, while the other 11 had a prolactinoma. Melatonin was given im at a dose of 20 mg at 09:00 h, and venous blood samples were collected at -20, 0, 20, 60, 120, 180 min. A normalization of PRL levels was achieved after melatonin injection in 3/8 patients with idiopathic hyperprolactinemia, while no effect was seen in patients with prolactinoma. Further studies, by evaluating the effect of a chronic treatment, will be required to define which is the action of melatonin on PRL release in PRL secretion disorders, and to evaluate its possible therapeutic role.