Diffuse pulmonary ^99mTc HM-PAO uptake associated with cigarette smoke exposure: A rat study

Normal biodistribution of ^99mTc-hexamethyl propyleneamine oxime (^99mTc HM-PAO) includes the liver, kidneys, and the brain and does not include the lung except for the lungs of cigarette smokers. To evaluate cigarette smoke exposure by ^99mTc HM-PAO pulmonary accumulation, 7 Long-Evans rats were exposed fo high levels of tar/nicotine cigarette smoke continously for 10 weeks; 7 sham (control) rats received room air in place of cigarette smoke. Five to ten minutes following intravenous injection of 300 μCi ^99mTc HM-PAO, a thoracoabdominal image was obtained from each rat by a gamma camera fitted with a pinhole collimator and interfaced with a Picker computer. The information from the ventral images of rats was also stored in a computer. Regions of interest over the liver and left lung were imaged. The mean lung/liver ratio for cigarette-smoke exposed rats was 1.17 (±0.037); the mean of sham (control) rats was 0.86 (±0.058). The lung uptake of cigarette smoke exposed rats was significantly higher (p = 0.0008) than that of control rats. While pulmonary function tests and morphometric examinations could not detect up to 12 weeks of smoke exposure, ^99mTc HM-PAO lung-imaging enabled detection of lung changes from in 10 weeks period cigarette smoke exposure. The mechanism of pulmonary ^99mTc-HM-PAO uptake is unknown and is subject to further evaluation.