Augmentation of prolactin release by α-melanocyte stimulating hormone is possibly mediated by melanocortin 3-receptors in the mouse anterior pituitary cells

Suckling- and estrogen-induced prolactin release from the anterior pituitary is mediated by α-melanocyte stimulating hormone (α-MSH) secreted by the intermediate lobe of the pituitary in the rat. Melanocortin 5-receptors are expressed in the anterior pituitary and probably mediate the α-MSH function. In contrast, the mouse anterior pituitary does not express the receptor. To examine whether or not α-MSH regulates prolactin release in mice, we performed cell immunoblot assay using anterior pituitary cells from adult female mice. We found that α-MSH acted on mammotrophs (prolactin-secreting cells) and stimulated prolactin release in a dose dependent manner. A series of RT-PCR using oligonucleotide primer pairs specific for each subtypes of melanocortin receptors revealed that the melanocortin 3-receptor is the sole receptor expressed in the mouse anterior pituitary. These results suggest that α-MSH-induced prolactin release is mediated by melanocortin 3-receptors in female mice.