[Morphological methods for analysing hormone secretory mechanism in the pituitary cells]

We introduce here two morphological methods of the rat anterior pituitary cells. In the first experiment, we showed immunofluorescence combined with a confocal laser scanning microscope. Distribution of actin was examined in growth-hormone (GH) secreting cells and folliculo-stellate cells and compared between in vivo and in vitro cells. In tissue, actin immunoreactivity was mainly limited near the plasma membrane. In cultured cells localization of actin clearly changed and the cells sometimes showed stress fiber-like structures in the cytoplasm. The cells also showed a small amount of alpha-actinin- and myosin-like immunoreactivities along stress fiber-like structures, which cannot be detected in the tissue cells. These data clearly showed differences in the localization of cytoskeletal proteins between in vivo and in vitro. In the second experiment, we showed electron microscopic analysis combined with monitoring hormone secretion in vivo. A catheter was inserted through the left external jugular vein into the right atrium of the heart. Through the catheter GH-releasing factor (GRF) and/or somatostatin was administered to freely-moving rats. Only about 30% of rats showed an increase in blood GH after GRF injection. Such responded rats were selected for our morphological analysis. From 5 min after GRF injection, the rats were infused with somatostatin or saline for 10 min. The treatment of somatostatin clearly diminished exocytotic figures from the plasma membrane.