The effect of structural modifications on the adrenal uptake of steroids labeled in the side chain with tellurium-123m.

A series of structurally modified steroids labeled in the side chain with Te-123m have been prepared and tested in rats to determine the critical structural features required for maximal adrenal uptake of this new class of potential adrenal-imaging agents. The Te-123m steroids investigated contained structural modifications of both the nucleus and side chain. Tissue distribution experiments and rectilinear scans indicated that 23-(isopropyl telluro)-24-nor-5 alpha-cholan-3 beta-ol (saturated nucleus), and 24-(isopropyl telluro)-chol-5-en-3 beta-ol (nuclear double bond) showed pronounced adrenal uptake after 1 day, with adrenal-to-liver ratios of 41 and 27, respectively. These results indicate that a combination of structural features is required for significant adrenal uptake of steroids labeled in the side chain with Te-123m. The structural requirements include a trans ring structure, an equatorial C-3 hydroxyl group, and a 17 beta side chain of moderate length.