The use of adjunctive drugs to alter uptake of 99mTc-Sn-pyrophosphate by myocardial lesions and bone.

Abstract A single intravenous injection of 1.25 mgm of vitamin D 3 (50,000 U.S.P. units) in rats caused a significant decrease in the uptake of 99m Tc-Sn-Pyrophosphate by bone when the radioactive compound was given 16 or 22 hours after vitamin D 3 and the rats were sacrificed 2 hours thereafter for determination of uptake. In rats with myocardial infarcts, produced by cautery under anesthesia, vitamin D 3 did not cause a significant decrease in uptake by infarct and in some instances even appeared to increase the latter uptake. Vitamin D 3 thus caused a significant increase in the ratio, uptake by infarct/uptake by bone. A single oral dose of 1.25 mgm of dihydrotachysterol had a similar effect, increasing the ratio, uptake by infarct/uptake by bone. In the large single dose used here, vitamin D 3 caused the expected increase in the concentrations of calcium and phosphorus in the serum. The effect on uptakes shown here is an example of the ability of a stable drug to influence significantly the distribution of a radioactive diagnostic drug. As bone is the chief non-target tissue degrading the quality of the image when 99m Tc-Sn-pyrophosphate is used clinically as a scintigraphic agent for the visualization of myocardial infarcts, an increase in the ratio, uptake by infarct/uptake by bone, is of interest.