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This study investigated the effects of long-term exposure of steady (19 dyne/cm2), 1-Hz non-reversing pulsatile (19+/-6 dyne/cm2) and 1-Hz purely oscillatory (0+/-19 dyne/cm2) shear stress on endothelial transforming growth factor-beta1 (TGF-beta1) mRNA expression. Cultured bovine aortic endothelial cells (BAECs) were systematically exposed to the three flow conditions for periods of 2, 6, 12 and 24 h, and relative differences in TGF-beta1 mRNA levels were measured by semi-quantitative RT-PCR. In response to steady shear stress, TGF-beta1 mRNA levels normalized to no-flow controls were 1.24, 1.42, 1.30 and 1.47 at the 2-, 6-, 12- and 24-h time points, respectively. In response to non-reversing pulsatile flow, these levels were 1.49, 1.64, 1.64 and 1.73, while the respective transcript levels for oscillatory flow were 1.33, 1.12, 1.12 and 1. 93. These results indicate that BAEC TGF-beta1 mRNA was up-regulated with the kinetics of the up-regulation faster for steady and non-reversing pulsatile flow than for oscillatory flow. Given the preferential localization of early atherosclerotic lesions in arterial regions exposed to low and/or oscillatory shear stress and the implication of TGF-beta1 as an athero-protective gene, these results are consistent with the notion that regions transiently exposed to oscillatory flow may be particularly prone to atherosclerosis.

It would be useful to have a clear definition of Male-Mediated Developmental Toxicity (MMDT) in order to make suggestions or recommendations for its investigation in the laboratory, but this not available. For the purposes of this document, MMDT will be considered to include all factors contributed by the male parent to the conceptus that can result in other-than-normal development.