Twenty-four hour secretory pattern of prolactin in hyperprolactinaemic patients with pituitary micro- and macroadenomas.

No nocturnal increase of prolactin (Prl) secretion during sleep has reportedly been discernible in most cases of hyperprolactinaemic patients with pituitary tumour. However, subjects previously evaluated, were in the majority, patients with large pituitary tumour. In the present study, 24 h secretory pattern of Prl was evaluated in 4 hyperprolactinaemic women with pituitary microadenoma and in 4 hyperprolactinaemic women with pituitary macroadenoma. Nocturnal increase of Prl secretion was observed in patients with microadenoma, but not in patients with macroadenoma. The nocturnal increase of Prl secretion in patients with microadenoma may reflect the function of the adenoma cells, and may suggest that the basic central nervous system programme governing Prl secretion in normals is qualitatively preserved in these patients. Alternatively, the nocturnal increase of Prl secretion may reflect the function of the normal lactotrophs remaining in these patients.