Eladio A. Nunez

Mitochondrial binding of triiodothyronine (T3)

SummaryTo assess the distribution of the thyroid hormone triiodothyronine (T3) within intact living cells, freshly prepared dispersed rat hepatocytes were incubated with [125I]-T3 for periods of 5 min and 30 min. Lightand electron-microscopic (EM) radioautography was carried out to determine the distribution of grains over the isolated cells. Both procedures showed the grains distributed almost entirely over the cytoplasmic matrix rather than the nucleus. Grain counts under the EM were compared with expectation based on established quantitative methods. Only the mitochondria showed obvious and statistically significant grain counts, whereas the nucleus failed to accumulate grains in excess of expectations by chance alone based on area. The findings support the existence of mitochondrial binding of T3, presumably a prerequisite for its action in direct stimulation of the mitochondria.

Specific paracrystalline structures of rough endoplasmic reticulum in the follicular (stellate) cells of the dog adenohypophysis.

SummaryThe fine structure of follicular cells of the adenohypophysis was examined in fetal, neonatal, and adult beagle dogs. Prior to birth, undifferentiated follicular cells are common. At birth mature cells that form follicles are routinely encountered. The fine structural appearance of follicular cells is unchanged between birth and adulthood. Follicular cells of puppies and adults are, however, distinguished by the presence of unusual complexes within distended cisternae of the rough endoplasmic reticulum. These complexes vary greatly in morphology, some appear as a maze of interconnecting tubules while others show a highly organized paracrystalline configuration. The presence of these paracrystalloid structures in follicular cells supports the view that they represent a distinct pituitary cell type.

Pituitary Serotonin: Responsiveness of Levels to Hormonal Change and Ultrastructural Alterations Associated with Amine Depletion*

SummaryThe level of serotonin in the pituitary gland of young dogs was significantly increased following treatment with thyroxine and after the injection of reserpine. Electron microscopic examination of the pituitary gland of thyroxine treated animals failed to reveal any ultrastructural alterations. Treatment with reserpine induced the appearance of annulate lamellae in the cytoplasm of cells containing very small granules and having the morphology of thyrotrophs. These observations suggest that biogenic amines within the gland may be involved in regulating the cellular activity of the pituitary.

Osteopetrosis: An interpretation of its pathogenesis

Two children with osteopetrosis were studied radiographically and histologically. It is concluded that the histopathologic finding of excessive retentions of chondro-osseous tissue and failure of remodeling of bones is the result of retarded osteocytic osteolysis and osteocytic chondrolysis.

Thyroid medullary carcinoma of the Djungarian hamster Phodopus sungorus: ultrastructural evidence for the production of normal and atypical intracellular granules

We have carried out an electron microscopic and immunocytochemical study of thyroid medullary carcinoma arising spontaneously in the Djungarian hamster, Phodopus sungorus. At the ultrastructural level the cytoplasm of tumor cells contained numerous round to slightly elongated, dense-cored secretory granules. The number of secretory granules differed from cell to cell in the tumor, being scanty in some cells but more or less abundant in most. Electron microscopic-immunocytochemistry demonstrated that all dense-cored secretory granules in all tumor cells exhibited calcitonin immunoreactivity. In approximately 10% of the tumor cells, unusual star-shaped secretory vesicles were also found in the cytoplasm. These vesicles contained a small, but well-defined, lucent core surrounded by a region of finely granular material of greater electron density. The outer contour of these unusual vesicles was stellate rather than smooth. They appeared to originate not from the Golgi complex, but from the rough endoplasmic reticulum. These atypical stellate vesicles did not show any calcitonin immunoreactivity. Furthermore, in a small number of tumor cells (approximately 1%) a third type of membrane enclosed structure was found. These were conspicuous rods 1-5 micron in length with tapering ends and a crystalline substructure. The presence of both normal and atypical secretory granules in some tumor cells suggests that carcinogenic transformation may interfere with the normal synthesis and assembly of secretory products by the cell.SummaryWe have carried out an electron microscopic and immunocytochemical study of thyroid medullary carcinoma arising spontaneously in the Djungarian hamster,Phodopus sungorus. At the ultrastructural level the cytoplasm of tumor cells contained numerous round to slightly elongated, dense-cored secretory granules. The number of secretory granules differed from cell to cell in the tumor, being scanty in some cells but more or less abundant in most. Electron microscopic-immunocytochemistry demonstrated that all dense-cored secretory granules in all tumor cells exhibited calcitonin immunoreactivity. In approximately 10% of the tumor cells, unusual star-shaped secretory vesicles were also found in the cytoplasm. These vesicles contained a small, but well-defined, lucent core surrounded by a region of finely granular material of greater electron density. The outer contour of these unusual vesicles was stellate rather than smooth. They appeared to originate not from the Golgi complex, but from the rough endoplasmic reticulum. These atypical stellate vesicles did not show any calcitonin immunoreactivity. Furthermore, in a small number of tumor cells (∼1%) a third type of membrane enclosed structure was found. These were conspicuous rods 1–5 μm in length with tapering ends and a crystalline substructure. The presence of both normal and atypical secretory granules in some tumor cells suggests that carcinogenic transformation may interfere with the normal synthesis and assembly of secretory products by the cell.

Separation of Parafollicular Cells from Thyroid Follicular Cells by Affinity Chromatography Using Thyroglobulin-Coupled Sepharose

Publisher Summary This chapter discusses a separation technique for separation of parafollicular cells from thyroid follicular cells by affinity chromatography using thyroglobulin-coupled sepharose. The thyroid parenchyma is comprised of two cell types: follicular and parafollicular cells. These cells are enmeshed in a highly vascularized connective tissue stroma that contains, in addition to the usual cellular and fibrous components, a large number of mast cells. Parafollicular cells produce, store, and secrete calcitonin. Parafollicular cells originate from the neural crest and, in a manner that is reminiscent of enteric neurons, associate with endodermally derived parenchymal cells and a mesenchymal stroma. The follicular and parafollicular cells do not differ very much in size. They are both approximately 10 μm in diameter at their widest point. In an experiment described in the chapter, it was found that follicular cells internalized the silica instead of resulting in a denser cell; the silica was toxic to the follicular cells and caused breakage of lysosomes and subsequent release of hydrolytic enzymes into the cytosol. An affinity column composed of thyroglobulin-coupled sepharose was successful in retarding the movement of TSH-stimulated follicular cells. Consequently, the ratio of parafollicular to follicular cells was considerably increased in certain fractions of the effluent, as were the concentration of 5-HT and the activity of SBP.