Prevention of benzene-induced myelotoxicity by nonsteroidal anti-inflammatory drugs.

Benzene affects hematopoietic progenitor cells leading to bone marrow depression and genotoxic effects such as micronucleus formation. Progenitor cell proliferation and differentiation are inhibited by prostaglandins produced by macrophages. Administration of benzene to DBA/2 or C57BL/6 mice caused a dose-dependent bone marrow depression and a significant increase in marrow prostaglandin E level and both were prevented by the coadministration of indomethacin and other inhibitors of the cyclooxygenase component of prostaglandin H synthase. Levels of benzene that decreased bone marrow cellularity also caused genotoxic effects measured as increased micronucleated polychromatic erythrocytes in peripheral blood, which was also prevented by the coadministration of indomethacin. These results suggest a possible role for prostaglandin synthase in benzene myelotoxicity; a mechanism by which this might occur is presented

Mechanical properties of the gastrocnemius aponeurosis in wild turkeys

In many muscles, the tendinous structures include both an extramuscular free tendon as well as a sheet-like aponeurosis. In both free tendons and aponeuroses the collagen fascicles are oriented primarily longitudinally, along the muscle's line of action. It is generally assumed that this axis represents the direction of loading for these structures. This assumption is well founded for free tendons, but aponeuroses undergo a more complex loading regime. Unlike free tendons, aponeuroses surround a substantial portion of the muscle belly and are therefore loaded both parallel (longitudinal) and perpendicular (transverse) to a muscle's line of action when contracting muscles bulge to maintain a constant volume. Given this biaxial loading pattern, it is critical to understand the mechanical properties of aponeuroses in both the longitudinal and transverse directions. In this study, we use uniaxial testing of isolated tissue samples from the aponeurosis of the lateral gastrocnemius of wild turkeys to determine mechanical properties of samples loaded longitudinally (along the muscle's line of action) and transversely (orthogonal to the line of action). We find that the aponeurosis has a significantly higher Young's modulus in the longitudinal than in the transverse direction. Our results also show that aponeuroses can behave as efficient springs in both the longitudinal and transverse directions, losing little energy to hysteresis. We also test the failure properties of aponeuroses to quantify the likely safety factor with which these structures operate during muscular force production. These results provide an essential foundation for understanding the mechanical function of aponeuroses as biaxially loaded biological springs