Influence of hypophysectomy and prolactin on the rat pinealocyte: a quantitative ultrastructural study.

The effects of hypophysectomy and prolactin administration on the ultrastructure of rat pinealocytes were studied by means of morphometric analysis. Hypophysectomy resulted in an increase in the Golgi apparatus and dense-core vesicles and a decrease in the granular endoplasmic reticulum, lysosomes and lipid droplets. Prolactin administration induced an increase in the granular endoplasmic reticulum and in the vacuoles which contained a flocculent material. Administration of prolactin to hypophysectomized rats raised the lowered levels of granular endoplasmic reticulum and lipid droplets to control values and caused an increase in vacuoles containing a flocculent material. Although hypophysectomy appeared to diminish the general activity of pinealocytes, it stimulated the neurosecretory-like secretory process Golgi apparatus-dense-core vesicles), whereas prolactin appeared to stimulate the ependymal-like secretory process (granular endoplasmic reticulum-vacuoles containing a flocculent material).