Method for the isolation of intact islets of Langerhans from the rat pancreas

A simple method for the isolation of intact islets from the normal rat pancreas is described. The method is based upon disruption of the acinar parenchyma by injecting Hanks solution into the pancreatic duct system followed by incubation of the pancreas in collagenase. Islets can be separated rapidly from this mixture by sedimentation. The isolated islets release insulin in vitro and appear normal by light and electron microscopy after incubation. A centrifugation method is also described for isolation of large quantities of islets for biochemical studies.

Location of sites of 5-hydroxytryptamine storage and metabolism by radioautography

1. A technique for the radioautographic identification, localization, and study of the turnover of cellular depots of 5-hydroxytryptamine (5-HT) has been evaluated. A light microscopic survey was made of the uptake and turnover of 5-HT, synthesized in vivo from its administered tritium-labelled precursor, 5-hydroxytryptophan (5-HTP).2. 5-HT was taken up rapidly and retained for long periods of time by adrenal medullary chromaffin cells, gastric enterochromaffin cells, blood platelets, thyroid parafollicular cells, beta cells of pancreatic islets, mast cells, and septal cells of the lung. Reticulo-endothelial cells of liver and spleen took up radioactive 5-HT more slowly but also retained it for days.3. Specific uptake, and a rapid turnover of radioactive 5-HT, was found in pancreatic exocrine cells, neurones of the superior cervical ganglion, terminal axons of gastro-intestinal myenteric plexus, carotid body cells, and pinealocytes.4. A supranuclear localization of radioactive 5-HT in renal proximal tubular cells may represent tubular secretion of 5-HT.5. The localization of 5-HT by radioautography generally corresponds to that found by formaldehyde-induced fluorescence. It makes possible the study of 5-HT turnover and is capable of greater resolution than the fluorescence technique. Freeze-drying may also be avoided.

Radioisotopic studies of the binding, exchange, and distribution of 5-hydroxytryptamine synthesized from its radioactive precursor

1. The synthesis, distribution, storage, and subsequent metabolism of 5-hydroxytryptamine (5-HT) produced in mice from the administration of its radioactive precursor, 5-hydroxytryptophan, has been investigated to form the basis for a similar study to be conducted by radioautography.2. Intravenous injection of the radioactive material was found to be essential for significant uptake of radioactivity by tissue. The duration of the period during which radioactive material was available for uptake by the tissue was 2 hr.3. The relative distribution of radioactivity in individual organs was studied and the radioactive compounds present in each were identified and quantitatively assayed. No unrelated routes of metabolism of the labelled material were found and radioautographic results may be interpreted in terms of the metabolic picture which emerged.4. Radioactive 5-HT was bound in tissues in preference to both its precursor, and metabolite, 5-hydroxytryptamine-O-glucuronide, and the radioactive 5-HT produced in vivo after the injection of labelled 5-hydroxytryptophan probably entered and labelled the endogenous 5-HT pool.5. Fixatives prepared with buffer solutions made hypertonic by the addition of sucrose could rapidly and effectively halt the movement of radioactive 5-HT out of tissues and prevent its subsequent extraction during histological processing.6. It is concluded that localization of sites concerned with 5-HT metabolism by means of radioautography is feasible and the 5-HT so localized will probably reflect the physiological compartmentalization of the amine.

Rapid release of the zymogen granule protein by osmium tetroxide and its retention during fixation by glutaraldehyde

Fixation by osmium tetroxide and glutaraldehyde of zymogen granules isolated from rat parotid and pancreas was investigated. Protein determinations showed that osmium tetroxide caused rapid release of most of the soluble protein of the granule during fixation in buffered isotonic sucrose. Such granules when examined in the electron microscope after shadow casting appeared quite flat, indicating that most of the contents had indeed been removed. Numerous damaged membranes of the granules were also observed. In contrast, zymogen granules fixed by glutaraldehyde and shadow cast essentially retained the spherical shape and the protein contents. The application of the shadow-casting technique in quantitative studies on the protein content of zymogen granules is discussed.