The carcinogenicity of thiamphenicol (TAP), an antibiotic drug, was examined in Fischer 344 rats of both sexes. TAP was given ad lib. in drinking water at levels of 0 (control), 125 or 250 ppm to groups of 50 male and 50 female rats for 2 yr. The treatment did not affect mortality and no toxic lesions were specifically induced. Furthermore, the incidence of tumours in the treated groups did not show any significant dose-related increase as compared with the control group. The results thus indicate that TAP is neither toxic nor carcinogenic, for any organs or tissues of F344 rats when given continuously at levels of 125 or 250 ppm in drinking water for 2 yr.

Administration, Oral↗

PubMedDate not supplied

Dose- and treatment duration-related effects of p-tert-octylphenol on female rats.

We conducted a study to investigate the relation between estrogenic effects of p-tert-octylphenol (OP) and serum concentration as well as treatment duration. Adult ovariectomized rats were given daily subcutaneous injections of OP for 2 and 14 days. 17beta-Estradiol was also administrated at a dose of 5 microg/kg. OP was detected in serum at doses of 25 mg/kg and above for 2 days and with multiple doses (14 days) of 12.5 mg/kg. Uterine weights and luminal epithelial height were increased although the effects were weak compared to 17beta-estradiol. Estrous conversion of the vaginal smear was detected only in 14-day-treated animals. OP-treatment for 2 days caused a dose-related increase in proliferation of uterine luminal, glandular, and stromal cells and vaginal epithelial cells. From the 14-day experiment, the minimum estrogenic dose level of OP was concluded to be 25 mg/kg/day and the serum level at the dose was determined to be about 80 ng/ml. These findings demonstrated that OP exerts estrogenic activity in the female reproductive tract of ovariectomized rats only at high levels of exposure and that the effects are fundamentally related to serum OP levels.

Animals↗

PubMedDate not supplied

Striped iron zoning of olivine induced by dislocation creep in deformed peridotites.

Deformation of solid materials affects not only their microstructures, but also their microchemistries. Although chemical unmixing of initially homogeneous multicomponent solids is known to occur during deformation by diffusion creep, there has been no report on their chemical zoning due to deformation by dislocation creep, in either natural samples or laboratory experiments. Here we report striped iron zoning of olivine ((Mg,Fe)2SiO4) in deformed peridotites, where the iron concentration increases at subgrain boundaries composed of edge dislocations. We infer that this zoning is probably formed by alignment of edge dislocations dragging a so-called Cottrell 'atmosphere' of solute atoms (iron in this case) into subgrain boundaries during deformation of the olivine by dislocation creep. We have found that the iron zoning does not develop in laboratory experiments of high strain rates where dislocations move too fast to drag the Cottrell atmosphere. This phenomenon might have important implications for the generation of deep-focus earthquakes, as transformation of olivine to high-pressure phases preferentially occurs in high-iron regions, and therefore along subgrain boundaries which would be preferentially aligned in plastically deformed mantle peridotites.

Journal Article↗

PubMedDate not supplied

Intracellular calcium response to directly applied mechanical shearing force in cultured vascular endothelial cells.

We studied the responses of cultured endothelial cells to mechanical shearing force directly applied to those cells in vitro to determine changes in the concentration of intracellular calcium ion (Ca++), one of the factors that transfers information within the cell. Cultured bovine fetal aortic endothelial cells containing the Ca++ fluorescence indicator, Fura-2, were rubbed with a latex balloon in a specially designed system, and changes in the fluorescence of Fura-2 caused by this shear stimulation were determined by photometric fluorescence microscopy. Immediately after shear stimulation, the concentration of Ca++ in the cells was increased and reached a peak (511 +/- 165 nM, n = 12) within 15 seconds after stimulation. After the peak, the concentration was gradually restored to the resting level (55 +/- 17 nM, n = 12). The magnitude of the Ca++ response was dependent on the intensity of the shear force applied. Analysis of fluorescence images of Fura-2 revealed that the cells showed this Ca++ reaction without being injured or desquamated, although there were slight differences in the degree and duration of reaction among cells. This reaction appeared even when the cells were placed in the air with no contact with the fluid. This result suggests that neither the fluid flow associated with the balloon movement nor chemical substances in the fluid are involved in the reaction, but that pure physical force alone is responsible for the Ca++ reaction. Further, it suggests that endothelial cells have the ability to perceive such physical stimulation as shear force and to transfer this information to the interior of the cell via changes in the intracellular Ca++ concentration.

Animals↗