The metabolism of inorganic sulfate in pancreatic acinar cells was studied by electron microscope radioautography in mice injected with sulfate-35S. Labeled sulfate was concentrated in the Golgi complex at 10 min. Within 30 min, much of the radioactive material had been transferred to condensing vacuoles. These were subsequently transformed into zymogen granules. By 4 hr after injection, some of the zymogen granules with radioactive contents were undergoing secretion, and labeled material was present in the pancreatic duct system. The Golgi complex in pancreatic acinar cells is known to be responsible for concentrating and packaging digestive enzymes delivered to it from the endoplasmic reticulum. Our work demonstrates that the Golgi complex in these cells is also engaged in the manufacture of sulfated materials, probably sulfated mucopolysaccharides, which are packaged along with the enzymes in zymogen granules and released with them into the pancreatic secretion.

Intracellular transport of sulfated macromolecules in parotid acinar cells was investigated by electron microscopic radioautography after injection of 35S-sulfate. Ten minutes after injection radiosulfate was concentrated in the Golgi region. By 1 hr, much of the radioactive material had been transported to condensing vacuoles. These vacuoles were subsequently transformed into zymogen granules which contained almost 70% of the radioactivity 4 hrs after injection. These results indicate that, in addition to its packaging function, the Golgi apparatus in parotid acinar cells is capable of utilizing inorganic sulfate for the production of sulfated macromolecules. These molecules, following an intracellular route similar to that taken by digestive enzymes, become an integral component of zymogen granules. The possibility that sulfated macromolecules play a role in exocrine secretion by aiding in the packaging of exportable proteins is discussed.

The sites of cell proliferation and the duration of the S‐phases in epithelia (tongue, stomach, duodenum, jejunum, ileum and descending colon) of the pouchless opossum, Marmosamitis, have been studied following the injection of tritiated thymidine. the sites of cell proliferation in these epithelia are not significantly different than those reported for rodent tissues. On the other hand, measurements of the mean duration of DNA synthesis revealed great variability in this phase: tongue (12.8 hr), stomach (>14.0 hr), duodenum (8.5 hr), jejunum (8.6 hr), ileum (9.7 hr) and descending colon (11‐3 hr). In addition, the values obtained for the mean duration of t2 (G2+2/1M) are fairly constant among the various epithelia. It is concluded that the times obtained for the average duration of the S‐phases are longer and more variable in M. mitis than similar observations reported on renewing epithelia of eutherian mammals.

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Mouse synovium was examined autoradiographically at various postinjection times to determine the pattern of ³⁵S utilization. Synovial cells incorporated ³⁵S in a manner consistent with synthesis and secretion of sulfated macromolecules. Ultrastructural examination demonstrated two cell populations, one with a structure indicative of phagocytic function, the other with a structure typical of secretory activity.