PRLR and pituitary gland adenoma: The present study clearly demonstrated the existence of six hPRL variants in human pituitaries with 2DGE and MS analyses, and its differential expression profile of six hPRL variants among different subtypes of pituitary adenomas; and confirmed that those six hPRL variants in human pituitary tissues were derived from hPRL prohormone with 227 amino acids (position 1–227), but not from mature hPRL with 199 amino acids (position 29–227).