Genomic DNA hybridizes with the same rate constant on the QCM biosensor as in homogeneous solution.

Hybridization rates of sheared, genomic E. coli DNA in 0.14 M, pH 6.7 phosphate buffer at 65 degrees C were determined by: (1) observing the rate of absorbance decrease at 260 nm due to self-hybridization in solution; and (2) measurement of the rate of mass increase caused by hybridization between DNA in solution and DNA photografted to polystyrene. The latter measurement was done using a quartz crystal microbalance (QCM). In both the spectrophotometric and QCM experiments the probe was identical to the target, as both were taken from the same sample of sheared E. coli DNA. In the QCM measurements, viscoelastic effects were made negligible by drying the biopolymer layer on the QCM's surface before taking the frequency readings. Our purpose was to explore the effect of immobilizing DNA on its hybridization rate constant. A second-order constant of 2.32 +/- 0.09 x 10(-6) ml microg(-1) s(-1), n = 14, for hybridization in solution was obtained spectrophotometrically, while the QCM experiment gave a constant of 2.2 +/- 0.3 x 10(-6) ml microg(-1) s(-1), n = 6. These values are not statistically different. The reaction half-lives for the spectrophotometric and QCM experiments were 6.5 h and 13 min, respectively. The shorter half-life on the QCM can be explained solely by the much greater reactant concentration in the QCM experiment. About 25% of the DNA was inactivated by the attachment reaction. After correcting for this, the surface-attached DNA hybridized with the same rate constant as DNA free in solution. Therefore, it is concluded that, in these specific experiments with genomic DNA, the immobilized regions must have been short compared to the length of the molecules. The data demonstrate the high hybridization rate obtainable when nucleic acids are hybridized in a thin-film, micro-volume reaction on a non-porous surface.

Carcinogenesis by methylbenzylnitrosamine near the squamocolumnar junction and methylamylnitrosamine metabolism in the mouse forestomach.

We repeated and extended a 1973 study by Sander and Schweinsberg on forestomach tumorigenesis in mice by methylbenzylnitrosamine (MBZN). Groups of 80 adult CD-1 mice of both sexes received 96 mg/kg of MBZN subdivided into 24 doses of 4 mg/kg, 12 doses of 8 mg/kg or 6 doses of 16 mg/kg (groups 1-3, respectively). The mice were injected i.p. twice weekly with MBZN in 30% dimethylsulfoxide and 6-8 mice/group were killed every 4 weeks up to 40 weeks. Ten untreated control mice did not develop forestomach tumors. Forestomach papillomas occurred in 35-53% of the treated mice, with the highest incidence and shortest latency (mostly <24 weeks) in group 3. Squamous carcinomas of the forestomach were found in 31% of group 1 and 4-6% of groups 2 and 3. Ninety-two percent of the carcinomas and 94% of the papillomas in the 8-mm wide forestomach occurred < or = 1 mm from the squamocolumnar junction (SCJ) with the glandular stomach. This is interesting in view of the rising incidence of human adenocarcinoma near the gastroesophageal SCJ. Methyl-n-amylnitrosamine (MNAN) yields 2-, 3- and 4-hydroxy-MNAN (HO-MNAN) in a 1:3:2 ratio when incubated with rodent tissues for which MNAN is carcinogenic. This metabolism may be due to cytochrome P450 isoform believed responsible for MNAN and, probably, MBZN activation. When freshly excised mouse forestomach and esophagus were incubated for 2 h with 23 microM MNAN, total HO-MNAN yields were 0.79 +/- 0.05 and 1.81 +/-0.08 nmol/100 mg tissue per h (mean +/- SE), respectively, with about 1:3:2 ratios between 2-,3- and 4-HO-MNAN. This compares with published mean HO-MNAN yields in nmol/100 mg per h of 1.2 for rat esophagus (where MNAN and MBZN are strongly carcinogenic) and <0.1 for rat forestomach. These findings may explain why MNAN and MBZN induce forestomach tumors in mice but not in rats and why MNAN induces esophageal tumors in mice, but does not explain why MBZN given i.p. fails to induce esophageal tumors in mice. Three sections of the mouse forestomach (closest-to to furthest-from the SCG) showed total HO-MNAN yields from MNAN of 0.61+/-0.05, 0.38+/-0.03 and 0.48+/-0.02 nmol/100 mg per h (mean +/-SE), respectively. This may help explain why the MBZN-induced forestomach tumors were non-centrated near the SCJ.

Evaluation of pregnant women after blunt injury.

A retrospective review of 125 pregnant women with blunt injuries admitted to a level I trauma center over a 35-month period was performed. The usefulness of three diagnostic tests, fetal ultrasound (US), external fetal monitoring (EFM), and Kleihauer-Betke (KB) tests in detecting fetal or pregnancy-associated complications was evaluated. The majority of women (77.6%) were involved in motor vehicle crashes and the mean injury Severity Score was low (4.7). The most common complications were premature uterine contractions (67%) and abruptio placentae (11%). When used together, EFM and US identified all complications. Moreover, all complications were manifest within 6 hours of admission. The KB tests had a sensitivity of 56%, a specificity of 71%, and an accuracy of 27%. We conclude that EFM and US are more useful in detecting fetal or pregnancy-associated complications after blunt injury. Monitoring can be limited to 6 hours if previous monitoring is normal. The KB test is of little use in the setting of acute trauma.