Carbon blacks are manufactured under controlled conditions for commercial use primarily in the rubber, painting, and printing industries. In contrast, soots are unwanted byproducts from the combustion of carbon-based materials for the generation of energy or heat, or for the disposal of waste. Unfortunately, the terms carbon black and soot often have been used interchangeably; however, carbon black is physically and chemically distinct from soot. Greater than 97% of carbon black consists of elemental carbon arranged as aciniform particulate. Depending on the type of soot, the relative amount of carbon (< 60% of the total particle mass), the type of particulate carbon, and particle characteristics (size, shape, and heterogeneity) can vary considerably. For both carbon black and soot, other elements and chemical compounds are associated with the particulate carbon. Total inorganics (ash) represent < 1% of the carbon black particle mass. Organic compounds can be extracted from particle surfaces (solvent extractable fraction [SOF]), and for carbon black, also are < 1% of the particle mass. Soots have much greater percentages of ash, SOF, or both, than carbon black. There has been concern about the adsorbed organic compounds because of potential biologic activity. For carbon black, the SOF is strongly adherent to carbon surfaces and is not released by biological fluids. The types of organic compounds consist primarily of unsubstituted polycyclic aromatic hydrocarbons and are not as biologically potent as those compounds present in soot. Thus, carbon black is distinctly different from soot, and when discussing potential health effects, care must be taken to differentiate between the two types of carbon-based particles.

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Immunocytochemical methods have been used to compare the cellular and subcellular distribution of nerve growth factor (NGF) and epidermal growth factor (EGF) in mouse submandibular glands. Rabbit antisera raised against purified proteins were characterized by immunoblot methods and were used to stain sections of salivary glands embedded in plastic. For light microscopy, antibodies were visualized by indirect immunofluorescence. For electron microscopy, thin sections were treated simultaneously with IgG against NGF and EGF coupled to colloidal gold particles of different size. Data indicate that NGF and EGF are present in all granular convoluted tubule cells and in no other cell type within the salivary gland. Ultrastructural analyses indicate that NGF and EGF are evenly distributed together within mature secretory granules, although a population of small granules was identified that is not immunoreactive for either protein. Taken together, the data suggest that granular convoluted tubule cells are homogeneous in the production and storage of NGF and EGF.

The influence of the medium T3 concentration on iodothyronine 5'-deiodinase activity was studied in cultured anterior pituitary cells derived from chronically hypothyroid rats. Type II (propylthiouracil-insensitive) enzyme activity, measured with T4 as substrate, was reduced by T3 in a dose-dependent manner, with an ED50 of approximately 1.4 X 10(-10) M free T3. Density gradient centrifugation was used to obtain populations of pituitary cells relatively enriched in thyrotrophs, somatotrophs, mammotrophs, or gonadotrophs, and the effect of T3 on type II 5'-deiodinase activity was evaluated in each of these four populations. In the absence of T3, the enzyme activity was 1.5- to 2-fold greater in the somatotroph- and mammotroph-enriched cell pools than in the thyrotroph- and gonadotroph-enriched pools. In contrast, when the cells were cultured in the presence of T3, enzyme activity was reduced to the same low level in all four enriched pools. The results suggest that the increase in whole pituitary type II 5'-deiodinase activity associated with hypothyroidism is due largely or totally to increases occurring within somatotrophs and mammotrophs. The data also suggest that the intrinsic responsiveness of the deiodinase to hypothyroidism is greater in somatotrophs and mammotrophs than in other anterior pituitary cells.