Intracellular Localization of 99mTc-d,l-HMPAO in Rat Blood

Objective: The objective of this study was to investigate the intracellular localization of technetium 99m-hexamethylpropylene amine oxime (99mTc-d,l-HMPAO) in rat red blood cells (RBCs) and plasma. Materials and Methods: Sprague-Dawley rats (n = 36) were injected with 129.5 MBq 99mTc-d,l-HMPAO. Using a heparinized syringe, 2-ml blood samples were withdrawn from the rats 10, 20, 30, 40, 50 and 60 min after 99mTc-d,l-HMPAO injection. Blood was centrifuged for 10 min at 2,240 rpm to separate RBCs from plasma. A chloroform/methanol/distilled water mixture was added to the RBCs and plasma in separate tubes to extract 99mTc-d,l- HMPAO into aqueous (Aq) and lipid (Lp) phases. The 99mTc-d,l-HMPAO activities in Aq and Lp phases were measured separately using a dose calibrator. The data were analyzed using Student’s t test and a one-way ANOVA. Results: More than 70% of the injected dose of 99mTc-d,l-HMPAO was retained in the RBCs for up to 60 min, compared to less than 20% in plasma. The uptakes in the Aq for plasma were 88.77 ± 1.04, 94.23 ± 2.42, 90.15 ± 1.88, 98.59 ± 0.89, 96.42 ± 1.50 and 97.59 ± 1.92% at 10, 20, 30, 40, 50 and 60 min after injection, respectively. The corresponding uptakes in the Lp phases were: 11.23 ± 0.04, 5.77 ± 0.07, 9.85 ± 0.06, 1.41 ± 0.08, 3.58 ± 0.04 and 2.41 ± 0.06, respectively. Similar values (% ± SE) and trends were obtained in the Aq and Lp phases for RBCs. A highly significant difference between the Aq and Lp phases at each time point studied was observed (p 0.0001). There was no statistically significant difference between the time points in the Aq phase, but there was a significant difference (p 0.001) between time points in the Lp phase. Conclusion: This study demonstrated that most of the intracellular localization of 99mTc-d,l-HMPAO was in the Aq phase compared to Lp phase in both RBCs and plasma up to 60 min.