Ultrastructural morphometry of the rat pituitary intermediate zone after stimulation and suppression

The intermediate zone of the rat pituitary was studied after stimulation for 3 weeks with the adrenostatic drugs metyrapone and aminogfutethimide and after suppression for 3 weeks with the glucocorticoid 6α-methylprednisolone using morphometry by the point-counting method on electron micrographs. After metyrapone, intermediate cells showed a significant (P <.05) increase in volume percentages of the smooth endoplasmic reticulum, the Golgi apparatus, and the lucent immature secretory granules, as well as a significant decrease in the lucent secretory granules, the vacuoles, the lysosomes, and the cell membranes in comparison with the untreated controls. After aminoglutethimide, the volume percentages of the nuclei, the smooth endoplasmic reticulum, and the dense and lucent immature secretory granules were significantly increased in comparison with the controls, whereas the unorganized cytoplasm, the lucent secretory granules, the vacuoles, and the lysosomes were significantly decreased. The morphological changes after both adrenostatic drugs clearly indicate the pathophysiologically expected increase of secretory activity. After 6α-methyfprednisolone, the rough endoplasmic reticulum, the vacuoles, and the lysosomes significantly decreased in comparison with the controls, and the smooth endoplasmic reticulum, the Golgi fields, and the immature secretory granules were increased. These changes cannot be interpreted without certain reservations as the first alterations indicate decreased activity, whereas the increased Golgi fields and immature secretory granules are usually signs of increased secretory activity, which cannot be expected after glucocorticoid treatment. The possible causes are discussed.