Intracellular Localization of ^99mTc-<i>d,l</i>-HMPAO in Rat Blood

Abstract

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 Using a heparinized syringe, 2-ml blood samples were withdrawn from the rats 10, 20, 30, 40, 50 and 60 min after ^99mTc-d,l-HMPAO injection.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.