ELECTRON MICROSCOPIC STUDIES ON THE SECRETORY MECHANISM OF PANCREATIC ISLET CELLS, WITH PARTICULAR REFERENCE TO BETA CELLS I. NORMAL SECRETION IN MICE, RATS, RABBITS AND CHICKENS, AND SECRETION STIMULATED BY A SINGLE INTRAVENOUS INJECTION OF GLUCOSE OR CHLORPROPAMIDE IN RATS

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Abstract
The ergastoplasm is a primary synthetic site of insulin or glucagon molecules carried by numerous microvesicles in moderate electron density toward the Golgi zone. These microcarriers constitute the lamellar component of the Golgi apparatus. Irregular swelling and shortening of the above lamellae occur and the vacuoles with amorphous raw substance are formed by pinching them off at their terminal dilated portions. At the Gglgi zone of [beta] cells of the animals, microfibrils approximately 60A in width attach on the outer surface of some of the above vacuoles, and occur both inside and through it; in rats, micro-vesicles may be frequently engulfed into sacs. Immature granules may develop and gain electron density gradually, followed by molding of the storage form of characteristic crystallization of mature granules The microfilamentous structures may fall into the sacs of secretory granules in [beta] cells, although less frequently. They are released by an emiocytotic process of secretion into the perisinusoidal space. The granule synthesis, storage and discharge in [beta] cells stimulated by a single intravenous injection of glucose or chlorpropamide were almost the same processes as found in the non-stimulated [beta] cells, except in the maximally effected state of glucose administration.