Effects of puncturing on the measurement of local oxygen pressure using polarographic microelectrodes

In situ oxygen utilization in the rat intervertebral disc

Nucleus pulposus cells of the intervertebral disc have no endogenous vasculature and have thus been hypothesized to be hypoxic. This hypothesis was tested using 2-nitroimidazole, EF5, a drug that at low oxygen concentrations forms covalent adducts with cellular proteins. After administrating EF5 to rats, sections of the intervertebral disc were analysed for EF5 adducts. Drug adducts were quantified in tissue sections using a fluorescent monoclonal antibody. Although the level of EF5 fluorescence in all intervertebral disc tissues was low, the transition zone at the periphery of the nucleus pulposus exhibited the highest level of EF5 binding. To substantiate this result, tissue nitroreductase levels and drug pharmacology were evaluated. Nitroreductase levels were measured in whole discs under severe hypoxia. We noted that there was robust EF5 binding to cells in the annulus fibrosus and transition zone with modest binding to cells of the nucleus pulposus and endplate. High-performance liquid chromatography analysis indicated limitations in EF5 access to the nucleus pulposus, most probably related to the lack of vasculature and slow drug distribution through the gel-like interior of the disc. However, despite diffusion problems, the drug dose was determined to be sufficient to report the oxygen status of the nucleus pulposus cells. Based on these findings, we conclude that despite poor vascularization, the disc cells accommodate to the local environment by displaying a limited need for oxygen. Accordingly, the cells of the intervertebral disc are not severely hypoxic.

Brain Tissue and Sagittal Sinus pO2 Measurements Using the Lifetimes of Oxygen-Quenched Luminescence of a Ruthenium Compound

The study was done to assess the performance of a system that measures the partial pressures of oxygen (pO2) from the lifetimes of oxygen-quenched luminescence of ruthenium compounds immobilized at the tip of fiber-optic optodes (Oxylite system). The system was used to measure the pO2 in brain tissue (thalamus and hypothalamus) and in the sagittal sinus of isoflurane-anesthetized rats at different FiO2's. The pO2 recorded in the hypothalamus (HPtO2) was consistently higher than the pO2 in the thalamus (TPtO2) at all FiO2. HPtO2 was closely related to PvO2 during normoxia but not during hypoxia. The equilibrium time of Oxylite system was found to be rapid compared to in vivo tissue response to changes in FiO2.