AMINO-ACID INFUSION BLOCKS RENAL TUBULAR UPTAKE OF AN INDIUM-LABELED SOMATOSTATIN ANALOG

The Indium-labelled somatostatin analogue pentetreotide has been succe ssfully developed for imaging of somatostatin receptor positive tumour s. However there is significant renal tubular uptake of the radiolabel led peptide, which can obscure upper abdominal tumours and would precl ude its use for targeted radiotherapy. The aim of this study was to de termine whether amino acid infusion, which has been shown to block ren al tubular peptide reabsorption, diminishes renal parenchymal uptake o f this radiolabelled analogue. Eight patients being scanned with the I n-111-labelled somatostatin analogue, pentetreotide, for localisation of gastroenteropancreatic tumours received an infusion of synthetic am ino acids. The ratio of isotope uptake in kidney to that in spleen was assessed, and compared to the ratio for matched control patients, to determine if amino acid infusion reduced renal parenchymal uptake of t he radiopharmaceutical. The amount of isotope in the urine was determi ned to ensure that any effect of the amino acid infusion was unrelated to changes in clearance. Infusion of amino acids significantly reduce d renal parenchymal uptake of isotope at 4 h. There was a non-signific ant increase in urinary clearance of isotope over the 4 h. consistent with reduced reuptake and a lack of effect on glomerular filtration ra te. This technique, by preventing renal damage, may allow the use of t his somatostatin analogue for local radiotherapy, and could be of wide r value in blocking tubular re-uptake of potentially nephrotoxic agent s, such as radiolabelled Fab fragments.