Subcellular compartmentation of prolactin in rat lactotrophs.

The intracellular localization of different molecular forms of prolactin was studied in various experimental models covering a wide range of secretory states. By correlating electron microscopy, morphometry and quantification of monomeric (small) and polymeric (big) prolactin after differential extraction procedures, big prolactin was found stored in secretory granules while small prolactin was loosely associated with all organelles involved in hormone synthesis and processing. No correlation with levels of lactotrophic secretory activity was detected by either the number of secretory granules or prolactin content in lactotrophs.