Chronology of chromosome reduplication in Chinese hamster cells incubated at low temperature

Experiments have been carried out on Chinese hamster fibroblasts. Cultures at the log-stage of growth were incubated at 15 or 25° C for 24 hrs. In two groups of experiments the cells were labeled with H³-TdR for 6 hrs at the respective temperature, washed and further incubated at 37° C. In each group of experiments cultures labeled with H³-TdR at 37° C for 20 min were used as a control. It was found: 1. the delay in the onset of cell passage through the mitotic cycle at 37° in cultures exposed to 15 or 25° C was about equal to 1,5-1 hr resp. and cells proceeded through the life cycle without blockages at any phase of the cycle; 2. the patterns of chromosome reproduction during the second half of the S-phase were the same after labeling at 15, 25 and 37° C. — In the third group the cells were labelled with HP-TdR for 10–60 min and 6 hrs resp. at 25° C. The patterns of reproduction of chromosome pairs 1–4 and small metacentrics were found to be the same in cells labeled briefly and those labeled for 6 hrs. After brief labeling asynchronous reduplication of different segments in many chromosomes became evident. It was masked because of heavy labeling after 6 hrs treatment.     

Magnetic resonance study of renal transplantation

In the last few years, we have focused our research effort on the magnetic resonance spectroscopic (NMR) studies of organ transplantation in the rat. P-31 NMR was employed to study changes in high-energy phosphates, intracellular pH in vivo of transplanted kidneys either during normal function, while undergoing the rejection process or subjected to other insults (e.g. ischemia, cyclosporine nephrotoxicity, urinary obstruction) which may also cause graft dysfunction. Nuclear magnetic resonance (NMR) parameters, specifically relative peak areas and intracellular pH, accurately distinguished among the different causes of graft dysfunction. Ureteral obstruction was clearly identified by elevations in the phosphodiester/urine phosphate peak. Ischemia and rejection were both associated with increases in inorganic phosphates and phosphomonesters and decreases in the beta-phosphate peak of adenosine triphosphate but were distinguishable from each other by differences in intracellular pH which was normal in rejected allografts (7.33 +/- 0.07, n = 3) and low in ischemic allografts (7.00 +/- 0.05, n = 3, p less than 0.05). Grafts insulted with cyclosporine toxicity were not distinguishable from normal allografts by any of the parameters studied. To determine the temporal relationship of NMR changes in allograft rejection, similar studies were performed serially in a group of rejecting (R) kidneys (n = 7) and compared with a control group of nonrejecting (NR) kidneys (n = 7). Major decrease in adenosine triphosphate (ATP) with increases in Pi and a marked increase in the Pi/ATP ratio were noted in the R allografts over time. The R allografts could be completely segregated from the NR allografts on the basis of the Pi/ATP ratio by day 7. These data suggest that 31P NMR spectroscopy may have potential clinical application in differentiating among the causes of graft failure of human renal allografts.     

Some features of oscillatory flow in a model bifurcation

Oscillatory flow in the lung is studied using an order-of-magnitude analysis and flow visualization experiments in a single bifurcation with lung-like geometry. The results are used to obtain a classification scheme that identifies three major flow regimes, distinguished on the basis of whether the flow is dominated by unsteadiness, viscous effects, or the effects of convective acceleration. The unsteady regime is found to exist for values of a dimensionless stroke length (L/a, i.e., stroke volume/local cross-sectional area) less than or equal to 3 and for values of a dimensionless frequency (alpha 2 = alpha 2 omega/nu, where alpha is airway radius, omega the oscillatory frequency, and nu the kinematic viscosity) less than or equal to 10 in basic agreement with previous studies. The viscous regime is found when alpha 2(L/a)(a/R)1/2 less than 10 and alpha 2 less than 10 where R is the local radius of curvature in the bifurcation; the convective regime is found when alpha 2(L/a)(a/R)1/2 greater than 10 and L/a greater than 3. This same approach yields scaling laws for the magnitude of secondary flow velocities and shows that the ratio of secondary-to-axial velocity is small everywhere outside of the convective regime where it scales with (a/R)1/2. Comparison of these results to related simple flows shows that many of the features observed can be attributed to the effects of curvature, suggesting that the influence of the flow divider and of area change may be of lesser importance than previously thought.