Comparative dual-tracer studies of carbon-14 tryptophan and iodine-131 HIPDM in animal models of pancreatic diseases.

Our previous studies have shown that a significant amount of the diamine derivative 131I-N,N,N'-trimethyl-N'-(2-hydroxy-3-methyl-5-iodobenzyl)-1,3- propanediamine (HIPDM) is taken up and retained by the normal pancreas. Therefore, we studied the uptake of [131I]HIPDM in various pathophysiological models in mice (chronic alcoholism, diabetes with beta-cell atrophy and obesity with beta-cell hypertrophy) and compared to 14C-L-Tryptophan (TRY) distribution in order to determine the factors influencing their pancreatic uptake. In normal animals, the pancreas uptake of TRY was generally higher than HIPDM. In diabetes, the relative concentration of both compounds was higher over the controls; however, in obesity, TRY showed lower accumulation than in controls while HIPDM showed no significant difference. Chronic ethanol (20%) ingestion increased TRY uptake in the pancreas compared to controls (36.88 +/- 3.21 vs. 30.03 +/- 4.17% ID/g; p less than 0.01) after 5 wk study period, but it decreased by 10 wk (22.36 +/- 0.95% ID/g; p less than 0.005). There were no significant changes in [131I]HIPDM distribution in alcoholics as compared to the controls. Radioiodinated HIPDM has potential advantages over [11C]TRY for pancreatic imaging since conventional imaging techniques can be employed. Our data, however, suggest that 11C-L-TRY is a more sensitive indicator of various pancreatic disorders.