Radiolabeling with organomercury compounds: Part 2. High specific activity synthesis of iodine-125 and iodine-131-6-iodocholest-5-en-3 beta-ol and its tissue distribution in rats.

Iodine-125 (125I) and iodine-131- (131I) 6-iodocholest-5-en-3 beta-ol has been prepared directly from 6-chloromercuricholest-5-en-3 beta-ol and [125I] or [131I]sodium iodide. This method produces material of "no-carrier-added" specific activity and excellent radiochemical purity. The entire procedure is complete in 10 min and can be carried out in 95% ethanol. The biodistribution of this new high specific activity form of [131I]-6-iodocholest-5-en-3 beta-ol has been measured in rats and found to be very similar to that found for low specific activity [131I]-6-iodocholest-5-en-3 beta-ol produced by exchange labeling. The whole-body elimination curve over a 4-day period was measured and a dependence between the rate of elimination and specific activity was detected. Products of three different specific activities in addition to "no-carrier-added" material were studied.