Seven methods of water activity (aw) measurement were tested in a collaborative study between three laboratories. These methods included the direct measurement of vapor pressure, an isopiestic technique and several electronic devices. Both saturated salt solutions and foods were measured. When compared to standards, the vapor pressure manometric (VPM) technique gave the best results. However, the absolute values of the standards are questionable. The results of the comparison of the values for foods showed a range of to.02 a, units. Thus, one can question the validity of literature values reported to three decimal places or the absolute values for limits on microbial growth. This research suggests that some standards must be set for all research groups and shows that overall, the VPM is probably the best and most accurate method
Glucose uptake into plasma membrane vesicles from the maternal surface of the human placenta was measured with the Millipore filtration technique. Uptake off D-glucose was dependent on the osmolarity of the incubation medium surrounding the vesicles. Uptake of D-glucose exceeded that of L-glucose. The uptake of D-glucose was not enhanced by placing 100 mM NaCl or NaSCN in the medium outside the vesicles (none inside) at the onset of uptake determinations. D-glucose transport was inhibited by cytochalasin B; phloretin, phlorizin, and 1-fluoro-2,4-dinitrobenzene. D-glucose uptake was inhibited by 2-deoxy-D-glucose, 3-O-methyl-D-glucose and to a lesser extent by D-galactose. It was not inhibited by alpha-methyl-D-glucoside. Cytochalasin B binding to the vesicles was 30% inhibited in the presence of 80 mM D-glucose. The results indicate that the system for facilitated transport of D-glucose at the maternal face of the placenta is distinctly different from that on the brush-border membrane of intestine or renal tubule and more closely resembles that of human erythrocyte.
Dialysable leukocyte extracts (DLE) may induce marked changes in the immune expression of human recipients. It is unclear whether the conversion of skin reactivity by DLE is due to a donor-related specific transfer factor or to an antigen nonspecific augmenting factor which enhances a preexisting low-level response in DLE recipients. In this study, DLE from immunized and unimmunized human and calf donors or saline was administered to 88 medical students. The recipient population demonstrated minimal background responses to the test antigens keyhole limpet haemocyanin (KLH) and horseshoe crab haemocyanin (HCH). The results indicate that the DLE preparations from both immunized and unimmunized donors significantly stimulated skin reactivity but not in vitro responses to both KLH and HCH in the recipient population. The results suggest that these DLE preparations contain an immunologically nonspecific augmentor, which stimulates a preexisting low-level response in the unimmunized population to become a clearly observable skin reaction.
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