Role of Glutathione in Lung Retention of 99mTc-Hexamethylpropyleneamine Oxime in Two Unique Rat Models of Hyperoxic Lung Injury
Journal of Applied Physiology
Rat exposure to 60% O2 for 7 days (hyper-60) or to >95% O2 for 2 days followed by a 24-hour in room air (hyper-95R) confers susceptibility or tolerance, respectively, of the otherwise lethal effects of subsequent exposure to 100% O2. The objective of this study was to determine if lung retention of the radiopharmaceutical agent 99mTc-HMPAO (hexamethylpropyleneamine oxime) is differentially altered in hyper-60 and hyper-95R rats. Tissue retention of HMPAO is dependent on intracellular content of the antioxidant glutathione (GSH) and mitochondrial function. HMPAO was injected i.v. in anesthetized rats and planar images were acquired. We investigated the role of GSH in the lung retention of HMPAO by pre-treating rats with the GSH-depleting agent diethyl maleate (DEM) prior to imaging. We also measured GSH content and activities of mitochondrial complex I and IV in lung homogenate. The lung retention of HMPAO increased by ~50% and ~250% in hyper-60 and hyper-95R rats respectively compared to retention in rats exposed to room air (normoxic). DEM decreased retention in normoxic (~26%) and hyper-95R (~56%) rats compared to retention in the absence of DEM. GSH content increased by 19% and 40% in hyper-60 and hyper-95R lung homogenate, compared to normoxic lung homogenate. Complex I activity decreased by ~50% in hyper-60 and hyper-95R lung homogenate compared to activity in normoxic lung homogenate. However, complex IV activity was increased by 32% in hyper-95R lung homogenate only. Furthermore, we identified correlations between the GSH content in lung homogenate and the DEM-sensitive fraction of HMPAO retention, and between the complex IV/complex I activity ratio and the DEM-insensitive fraction of HMPAO retention. These results suggest that increase in the GSH-dependent component of the lung retention of HMPAO may be a marker of tolerance to sustained exposure to hyperoxia.