Transgenic mice over-expressing galanin exhibit pituitary adenomas and increased secretion of galanin, prolactin and growth hormone

Galanin is a biologically active 29 amino acid peptide, widely distributed in the central and peripheral nervous system, and most abundantly in the hypothalamus where it may serve in the regulation of anterior pituitary hormones. We herein report that mice carrying the rat preprogalanin cDNA specifically targeted to the somatomammotroph cell lineage, under the control of the rat GH promoter, over-express and over-secrete galanin. Galanin peptide is localised within the GH and prolactin secretory granules. GH and prolactin release is increased as well, predominantly in males, while older transgenic animals develop pituitary hyperplasia and adenoma. In both male and female transgenic mice there is a significant increase in serum galanin (P<0.00003 and P<0.001 respectively) and prolactin (P<0.002 and P<0.05 respectively) levels, while only in male transgenic mice is there a significant increase in the serum levels of GH. Furthermore, in male transgenic mice serum prolactin levels are significantly correlated with the serum galanin levels (P<0.03). We conclude that galanin plays a key role in the process of pituitary hyperplasia, acting as a growth factor to promote pituitary cell proliferation, and participates in pituitary adenoma formation not necessarily dependent on oestrogens. Targeted over-expression and over-secretion of galanin in the somatomammotroph cell lineage stimulates predominantly hyperprolactinaemia in an oestrogen-independent manner.