The effect of DMSA loading on the renal handling of technetium-99m in rats

The renal handling of technetium-99m dimercaptosuccinic acid (99mTc DMSA) was studied in rats treated with high doses of nonradioactive DMSA to inhibit the renal uptake mechanism(s). A static scan was obtained 1 hour after the intravenous (iv) injection of 99mTc DMSA and the radioactivity in kidneys and bladder was calculated as a percentage of the injected amount. Total glomerular filtration rate (GFR) and effective renal plasma flow were also determined. Preloading with DMSA caused a fall in the renal accumulation of 99mTc DMSA together with a small increase in the amount excreted into the urinary bladder. Despite a stable GFR, the total amount of 99mTc DMSA handled by the kidneys (i.e., renal plus bladder activity) was reduced. These findings are compatible with the hypothesis that peritubular uptake and subsequent intracellular fixation are of importance in the renal accumulation of 99mTc DMSA. On the other hand, the radioactivity excreted into the urine probably stems from non-reabsorbed 99mTc DMSA initially filtered by the glomeruli.