Ultrastructural immunocytochemical localization of prolactin and growth hormone in the porcine pituitary.

The immunocytochemical peroxidase-antiperoxidase technique was used to identify prolactin- and growth hormone-producing cells in the porcine pituitary at the ultrastructural level. The growth hormone-producing cells contain round secretory granules (300 nm to 500 nm in diameter). The prolactin-producing cells can be identified by their distinct round and ovoid secretory granules which vary in size. Most of these cells contain large granules (450 nm to 750 nm in diameter), but some prolactin-producing cells display smaller secretory granules (250 nm to 500 nm). The two hormones were localized exclusively in the secretory granules. Staining for prolactin was observed in round and ovoid granules, as well as in small and polymorphic granules within the Golgi complex. This study confirmed (i) that the two hormones are located in different cells, and (ii) that under normal physiological conditions no one cell can synthesize and store both hormones simultaneously.