In vivo characterization of renal iron transport in the anaesthetized rat

1. In vivo microinjections of (FeCl3)-Fe-55 were made to assess renal iron (Fe2+/3+) transport in the anaesthetized rat. 2. Following microinjection into proximal convoluted tubules (PCTs), 18.5 /- 2.9% (mean +/- S.E.M., n = 11) Of the Fe-55 was recovered in the urine. This recovery was not dependent on the injection site indicating that iron is not reabsorbed across the surface convolutions of the proximal tubule. 3. Following microinjection into distal convoluted tubules (DCTs) 46.1 +/- 6.1% (n = 8) of the injected Fe-55 was recovered. Taken together the recove ry data from the PCT and DCT microinjection studies indicate that the trans port of iron occurs in the loop of Henle (LH) and collecting duct system. 4. In vivo luminal microperfusion was used to examine iron transport by the LR in more detail. In tubules perfused with 7 mu mol l(-1) (FeCl3)-Fe-55, 52.7 +/- 8.3% (n = 8) of the perfused Fe-55 was recovered in the collected fluid, indicating significant iron reabsorption in the LH. Addition of copp er (Cu2+ as 7 mu mol l(-1) CuSO4), manganese (Mn2+ as 7 mu mol l(-1) MnSO4) or zinc (Zn2+ as 7 mu mol l(-1) ZnSO4) to the perfusate did not affect rea bsorption of water, Na+ or K+, but increased recovery of Fe-55 to 83.5 +/- 6.8% (n = 8, P < 0.04), 75.8 +/- 5.9 (n = 6, not significant, n.s.) and 67. 9 +/- 3.8; (n = 9, n.s.), respectively. 5. Thus, iron transport in the LH can be reduced by the addition of copper or manganese to the luminal perfusate suggesting that these ions may compet e with iron for a common transport pathway. However, this pathway may not b e shared by zinc.