Effect of training on cardiovascular response to exercise in women.

Seventeen women (mean age 31 yr) participated in a training program divided into an initial 9-wk period and a subsequent 52-wk period, during which time 6 continued to exercise and the remainder detrained. Improvements in VO2max were significant (+34%) during the initial 9 wk and small (+5%) for the final 52 wk. Four women who stopped training showed a decrease in VO2max (-10%) during the last phase. During the initial 9 wk, central adaptation was important, with SV showing an increase of 28% at 80% VO2max. Peripheral adaptation (a-v O2 difference) was unchanged. Subjects who trained an additional 52 wk showed a slight drop in SV at submaximal work loads from the initial increase following the first 9 wk. When compared with the initial test the change at 9 wk in peripheral adaptation was a small and nonsignificant rise, followed by a significant increase at 61 wk. Women who are very unfit initially (predicted VO2max of 28 ml/kg-min), apparently adapt to the initial training with a central change followed by a much stronger peripheral adaptation during a longer training program.     

A method of synchronization of normal and malignant human cells in culture.

A method is described for providing reproducible S phase parasynchrony in both normal mesenchyme and transformed epithelia. Cells were seeded at low density in medium containing 10% serum. 24 h later the serum concentration was reduced to 0.5%. After 110th the cells were collected at the G1/S boundary in fresh medium containing 10% serum plus 2.5mM hydroxyurea over 20h. After removal of hydroxyurea and trypsinization the re-plated cells entered the S phase with a high degree of synchrony, as judged by autoradiography, pulse-labelling with 3H-thymidine, cell growth and time lapse cinematography. By 6h after synchronization 80% of the population had entered the S phase and between 10-13h 70% went through mitosis.     

The ability of Tilapia mossambica (Peters) to enter deep water

Juvenile Tilapia mossambica (Peters) are extremely tolerant of depth and can compensate to a depth increase of 0 to 33 m in a few minutes. As the fish grow they become less able to compensate to deep water. At a total length of 15–18.5 cm small adult male T. mossambica can compensate to 20 m whereas females can only compensate to 13 m. Large adults (20–25 cm) of both sexes compensated to 11.5 m (range 9.5–13 m). Adult fish require 4 to 7 days for maximum depth compensation at 22°C. Analysis of the oxygen content of the swimbladder indicated that this gas accounts for over half the gas in surface equilibrated fish. Oxygen secretion into the swimbladder appears to be the mechanism of equilibration at depth.     

Length dependence of rate constants for end-to-end association and dissociation of equilibrium linear aggregates

A semi-quantitative analysis is given of the length dependence of the rate constant for association (annealing) of two long linear aggregates in solution. The equilibrium constant for this process, or its inverse (fragmentation or dissociation), is relatively easy to formulate from appropriate partition functions. From these two ingredients, the length dependence of the rate constant for spontaneous fragmentation can be deduced. Numerical examples are included.