The concentration of reduced cytochrome b5 has been monitored in microsomal preparations during stearoyl-CoA desaturation in the presence and absence of thyroxine. During 30-min incubations, 20 μm thyroxine caused an apparent 210% stimulation of NADPH-mediated desaturation. In control reactions, the concentration of reduced cytochrome b5 increased and the concentration of oxygen decreased during the first 6 to 8 min of incubation. At the end of this time, oxygen concentration was at a level of less than 2% of air-saturated levels, cytochrome b5 was fully reduced, and the desaturation reaction had stopped. In thyroxine-containing reactions, the oxygen concentration and the rate of desaturase activity were maintained at high levels throughout the incubation. The reduced cytochrome b5 concentration achieved a maximum, partially reduced level early in the reaction which was maintained during the incubation. In reactions which contained small amounts of NADPH (in which reoxidation of cytochrome b5 can be observed), thyroxine slowed the rate of such reoxidation. Therefore, the apparent thyroxine stimulation of in vitro microsomal fatty acid desaturation may be caused by the inhibition of nondesaturase oxygen-utilizing reactions. Oxygen depletion is prevented, thereby allowing the oxygen-dependent desaturation reaction to proceed.

The important interplay between blood circulation and vascular cell behavior warrants the development of highly sensitive but small sensing systems. The emerging micro electro mechanical systems (MEMS) technology, thus, provides the high spatiotemporal resolution to link biomechanical forces on the microscale with large-scale physiology. We fabricated MEMS sensors, comparable to the endothelial cells (ECs) in size, to link real-time shear stress with monocyte/EC interactions in an oscillatory flow environment, simulating the moving and unsteady separation point at arterial bifurcations. In response to oscillatory shear stress (τ ) at ± 2.6 dyn/cm2, time-averaged shear stress (τave) = 0 at 0.5 Hz, individual monocytes displayed unique to-and-fro trajectories, undergoing rolling, binding, and dissociation with other monocyte, followed by solid adhesion on EC. Incorporating with cell-tracking velocimetry, we visualized that these real-time events occurred over a dynamic range of oscillating shear stress between ± 2.6 dyn/cm2 and Reynolds number between 0 and 22.2 in the presence of activated adhesion molecule and chemokine mRNA expression.