Amplification of nocturnal melatonin secretion in women with nocturnal hyperprolactinemia

In order to assess the pathophysiological role of melatonin (MLT) in nocturnal hyperprolactinemia (NH), nocturnal serum MLT and prolactin (PRL) levels were measured in samples collected every 2h over a 12-hour period (2000h-0800h) from 5 normal women and 9 women with NH under physiological light/dark condition (lights off from 2100h to 0600h). Furthermore, differences in the PRL response to acute oral administration of MLT (1 mg or 5 mg) during the daytime between the 2 groups was studied. Nocturnal MLT levels in patients with NH were significantly higher (p < 0.02) than in normal women. The maximal PRL levels (52.6 +/- 26.7 ng/ml at 2400h) during the night in patients with NH were significantly higher (p < 0.05) and were reached 4h earlier than in normal women. The response to administration of 1 mg of MLT was not different between the 2 groups. However, administration of 5 mg of MLT to normal women resulted in a rapid and prominent PRL release, similar to that observed at nighttime in patients with NH. These results indicate that the abnormal PRL release in patients with NH is not due to higher sensitivity to MLT. However, the elevated MLT levels in patients with NH may be related to the neuroendocrine disorder.