Analysis of accumulation of 99mTc-octreotide and 99mTc-EDDA/HYNIC-Tyr3-octreotide in the rat kidneys

The aim of this study was to compare renal handling and distribution of 99mTc-octreotide and 99mTc-EDDA/HYNIC-Tyr3-octreotide (HYNIC-TOC) in rats. In kidney perfusion experiments, the renal clearance value of 99mTc-octreotide was three times lower than that of 99mTc-EDDA/HYNIC-TOC. The predominant renal excretion of 99mTc-EDDA/HYNIC-TOC was associated with a high and long-term renal accumulation up to 48 hrs. Microautoradiographic results indicated that 99mTc-EDDA/HYNIC-TOC was retained mainly in the renal medulla within the cells of the collecting ducts and in the surrounding tissue. Lower positivity was found in the proximal and distal tubular cells. We conclude that the mechanism of renal accumulation of somatostatin analogues renal accumulation is complex and that proximal tubular reabsorption is probably not the main mechanism for uptake of 99mTc-EDDA/HYNIC-TOC in the kidneys. The presence of the somatostatin receptors, differences in the tonicity level within kidneys and other possible mechanisms could participate in their renal accumulation