Large secretory granules in ACTH secreting cells of corticosterone injected rats

The number and size of secretory granules were studied in ACTH secreting cells of adrenalectomized rats injected with corticosterone. In corticosterone injected, adrenalectomized rats, degranulation occurred inasmuch as the steroid was begun 24 hr after adrenalectomy; during the reaccumulation phase, aggregates of secretory granules and large secretory granules measuring up to 300 μm in diameter were observed in focal areas beneath the plasma membrane. Adrenalectomy and sham injection caused a significant reduction in the number of mature secretory granules. The population of immature secretory granules in the region of the Golgi apparatus on the other hand was significantly elevated in adrenalectomized sham injected rats. Plasma corticosterone, determined by a protein binding assay, was significantly elevated in steroid injected animals; no corticosterone was detected in the plasma of adrenalectomized animals.