During the first 3 days of exposure of rats to 5°C, the nitrogen concentration of interscapular brown fat increased by 50% and remained at this elevated level for the duration of the 8-wk observation period, while the mass of tissue increased fourfold. The concentration of both DNA and RNA per unit nitrogen reached a maximum after 3 days, then declined; however, the total quantity of each continued to rise. The concentration of various respiratory enzymes decreased during the first few days and then increased, but at different rates. The morphological changes in mature brown fat cells during cold acclimation were observed to be: a reduction in fat droplet size during the first 3 days, followed by a gradual increase in size through 6 wk in the cold; a continual increase in the amount of intermitochondrial ground substance during the first 3 wk, with increased granularity and glycogen content after 1 wk; initial disappearance of glycogen between mitochondria, followed by the reappearance of a few isolated particles in the intermitochondrial ground substance after 1 wk in the cold; initial increase in the density of intramitochondrial matrix for the first 3–4 days, followed by a gradual return to the control density; loss in integrity of mitochondrial outer membranes during the first 4 days, followed by gradual but incomplete restoration; temporary loss of the dense material in lipid droplets during the first 24 hr, with return after 1 wk in the cold; and a 40% increase in mitochondrial diameter within 1 day, followed by a decrease in diameter within 1 wk to a constant value about 15% larger than the controls.

The EMT6 mouse tumor was selected for use in the study of cytocidal activity and proliferative ability of infiltrating macrophages because of its high plating efficiency when explanted to culture. The plating efficiency for cells directly plated in culture from the tumor was 28 +/- 9.3%, irrespective of the size of the tumor. Of the adherent cells derived from the tumor, the fraction that was macrophages increased from 27% at 7 days to 47% at 28 days after initial injection. Time-lapse cinemicrography was used to directly observe adherent cells derived from the tumor, and macrophages were found to be cytocidal. When grown in the presence of L-cell conditioned medium no macrophage colonies were found when cultures were established from untreated mice even though most tumor cell colonies contained macrophages. When mice were first treated with 0.8 mg BCNU prior to establishment of the cultures, in order to reduce the frequency of colony-forming tumor cells, approximately half the colonies found contained only macrophages. These results show that macrophages in this tumor are cytocidal and capable of proliferation.

Proliferation and death were measured in synchronously growing cultures of HeLa S3 cells during treatment with up to 30 mM caffeine. Changes in the number of colony-forming cells were determined by single-cell plating, while changes in the total number of cells were measured both by electronic counting and by monitoring cell division and physiological death cinemicrographically. At concentrations between 2 and 5 mM, cell killing occurs over several days during which the cells traverse the generation cycle once or a few times before losing colony-forming ability, with consequent proliferation of non-colony-forming cells. This indicates that lethal damage is accumulated with time. Death occurs more rapidly at higher concentrations, without proliferation, the kinetics of inactivation being strongly dependent on the phase of the cycle (cell age) at which treatment is initiated. G1 cells are killed more slowly in 10 mM caffeine than are S cells, but G1 cells respond rapidly to 20 mM caffeine, suggesting the inception of an additional mode of killing. The incidence of sister-cell fusion increases with increasing caffeine concentration above 1 mM. On addition of 10 mM caffeine to a culture prepared from collected mitotic cells, the cells undergo a transient rounding and then respread after several hours; with 20 mM, they never respread. The generation cycle is prolonged in a concentration-dependent fashion, as is the duration of G1; the generation time is doubled in 5-6 mM caffeine. G2 and M are also prolonged at concentrations above 3 mM, but S is not prolonged even by 10 mM caffeine.

No abstract

No abstract