RISE OF PLASMA PROLACTIN AND CHANGES IN FINE-STRUCTURE OF THE ANTERIOR HYPOPHYSIS AFTER PITUITARY-STALK SECTION IN RATS

The effects of pituitary stalk section on the plasma PRL concentration and structure of PRL cells were studied in rats with the use of RIA and electron microscopy. The pituitary stalk was transected in the estrous rat using the parapharyngeal route and blood samples were withdrawn through a cardiac cannula before and after surgery. Plasma PRL concentrations increased significantly 4 min after stalk section. Plasma PRL levels were significantly elevated to one of the highest levels within 8 min after stalk section, and these high levels were maintained until the end of the experiment 2 h after stalk section. No significant changes occurred in sham-operated rats. Ten minutes after stalk section, secretory granules of PRL cells were decreased in number, and most granules were arranged in the peripheral zone of the cytoplasm. The Golgi apparatus and the rough-surfaced endoplasmic reticulum were well developed. Thirty minutes after stalk section, PRL granules were markedly decreased and an abundance of immature granules was observed in the well developed Golgi area. Exocytosis of PRL cell granules was more frequently encountered at 30 min than at 10 min. Cisternae of the endoplasmic reticulum were markedly enlarged at this stage. It is suggested that removal of PRL release-inhibiting factor supply from the hypothalamus to the pituitary gland immediately stimulates activity of PRL cell organelles for release and synthesis of PRL. © 1979 by The Endocrine Society.