Partial characterization of a parathyroid hormone-stimulated resorption factor(s) from osteoblast-like cells.

PTH stimulates osteoblast-like cells to produce a product(s) capable of increasing cellular bone resorption. We have investigated this phenomenon using primary cultures of osteoblasts and the clonal osteoblast-like cell line ROS 17/2. Conditioned medium from PTH-stimulated populations of either culture increases bone resorption compared to conditioned medium measured in three independent assay systems; the isolated osteoclast assay system, elicited macrophages, and the fetal bone rudiment system. Characterization of the factor(s) of PTH-stimulated osteoblast-like cell (ROS 17/2) suggests that the compound(s) is not prostaglandin (no inhibition by indomethacin; not extractable in diethylacetate). Rather, it is heat and protease sensitive. In addition, secretion of the product is sensitive to cycloheximide. These findings lead us to the conclusion that the factor(s) is protein. Further work demonstrates the necessity for a divalent cation for retention of factor activity. Finally, we have estimated the molecular radius of the factor as about 110,000 daltons and perhaps a second at about 70,000 daltons using a sizing column. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of [35S]methionine-labeled PTH-stimulated ROS culture supernatants reveals relatively increased secretion of proteins with these approximate molecular radii.

Endogenous digoxin-like immunoreactive factors eliminated from serum samples by hydrophobic silica-gel extraction and enzyme immunoassay.

Elimination of endogenous digoxin-like immunoreactive factors (DLIF) that interfere with accurate measurement of digoxin requires use of a highly specific anti-digoxin antibody, or that DLIF be separated from digoxin before immunoassay. Several commercial digoxin-assay kits include a step for separating serum proteins and other substances from digoxin before immunoassay. We tested six different immunoassay methods (some having pretreatment steps) for their ability to detect DLIF in serum from patients in renal failure, pregnant women, and neonates, all of whom were not taking digoxin. Extracting digoxin on a column of derivatized silicagel eliminated detectable DLIF from serum as measured by enzyme immunoassay (EMIT; Syva Co.), but recovery of added digoxin was quantitative. In contrast, protein precipitation with 5-sulfosalicylic acid left significant amounts of DLIF in samples, most probably because the procedure (TDx assay; Abbott Labs.) disrupted protein-DLIF binding. A glass-bead radioimmunoassay (Immophase; Corning Medical) had the most digoxin-specific antisera. By preparative silica-gel-chromatography of serum we could eliminate or significantly minimize inaccurate digoxin measurements attributable to endogenous DLIF.

Effect of sodium ortho-iodobenzoate on oxygen transport and erythropoiesis in hypoxemic dogs with a right-to-left cardiac shunt.

Eight dogs were made hypoxemic by surgical construction of a right-to-left cardiac shunt; and they were given sodium ortho-iodobenzoate (OISB) before and for 3 months after operation. The P(50) at 50% saturation) rose from 27.2 +/- 0.7 to 31.2 +/- 0.6 mm Hg (p less than 0.001) during OLSB treatment before operation and increased further to 32.2 +/- 0.8 mm Hg 3 months after creation of hypoxemia. The P(50) remained elevated for an additional 3 months after OISB was stopped. Administration of OISB before operation did not alter the red blood cell 2,3-diphosphoglycreate concentration. Hypoxemia caused an increase of this metabolite from 0.91 +/- 0.21 to 1.50 +/- 0.28 moles/moles of hemoglobin (p less than 0.05); the rise was not as great as that observed in hypoxemic dogs without OISB treatment. In spite of significant hypoxemia, hematocrit rose only slightly during the period of OISB infusion. OISB increased P50 and prevented the compensatory polycythemia regularly seen when dogs are made hypoxemic. Altering oxygen transport in this fashion may increase tissue oxygen delivery in patients with conditions which result in tissue hypoxia.