Influence of prolactin on the ultrastructure of the rat pinealocytes in vitro: a quantitative study

A quantitative ultrastructural study was performed on the influence of prolactin on various cell organelles in the rat pinealocytes in vitro. An increase in cross-sectional areas of mitochondria, Golgi apparatus, granular endoplasmic reticulum, lipid droplets and vacuoles containing flocculent material as well as in the number of dense-core vesicles was observed in the pinealocytes in the glands cultured for 12-h in prolactin-containing medium. These results indicate that in vitro prolactin stimulate general cell activity as well as both putative pinealocyte secretory processes (i.e., neurosecretory-like and ependymal-like).