Experimental approach of mechanisms involved in the transfer of ingested neptunium

The author have studied in rats the in vivo transfer through jejunal segments of different soluble forms of Np (5.10/sup -12/ to 9.10/sup -4/M) in NaCl 0.9% at pH 7. At 5.10/sup -12/ M the jejunum is permeable to Np(V) nitrate and as much as 2.7% of the activity in the lumen is transferred per 10 cm per hour. As Np(V) is not complexed, the addition of DTPA Ca (100 μM) does not significantly modify this value. On the contrary 1 mM citrate decreases the transfer to 0.8%. Np(IV) is readily transformed to Np(V) when the pH is raised to 7, the pH of the working solution. In these conditions, citrate (1 mM) and DTPA Ca (100 μM) stabilize Np(IV) and the observed transfers, 0.3% and 0.9% respectively, are lower than those of Np(V) in similar solutions. Whatever the Np(V) solution used, tissue distribution of transferred Np is similar. Tissue distribution of complexed Np(IV) is quite different and varies as a function of the chelator used. Using Np(V) nitrate at different concentrations, the transfer decreases with decreasing concentration down to 10/sup -5/ M. This could correspond to a limited flux of Np through the jejunal epithelium estimated at 4 nM/10 cm/hour. Finally, histology demonstrates that after gavage in vivo with Np at masses that increase the f/sub 1/ at least 10 times, no alteration of the intestinal barrier can be established