Intestinal iron uptake in the European flounder (Platichthys flesus)

dIron is an essential element because it is a key constituent of the metall oproteins involved in cellular respiration and oxygen transport. There is n o known regulated excretory mechanism for iron, and homeostasis is tightly controlled via its uptake from the diet. This study assessed in vivo intest inal iron uptake and in vitro iron absorption in a marine teleost, the Euro pean flounder Platichthys flesus. Ferric iron, in the form (FeCl3)-Fe-59, w as reduced to Fe2+ by ascorbate, and the bioavailability of Fe3+ and Fe-2were compared. In vivo Fe-2+ uptake was significantly greater than Fe3+ upt ake and was reduced by the iron chelator desferrioxamine. Fe2+ was also mor e bioavailable than Fe3+ in in vitro studies that assessed the temporal pat tern and concentration-dependency of iron absorption. The posterior region, when compared with the anterior and mid regions of the intestine, was the preferential site for Fe2+ uptake in vivo. In vitro iron absorption was upr egulated in the posterior intestine in response to prior haemoglobin deplet ion of the fish, and the transport showed a Q(10) value of 1.94. Iron absor ption in the other segments of the intestine did not correlate with haemato crit, and Q(10) values were lower. Manipulation of the luminal pH had no ef fect on in vitro iron absorption. The present study demonstrates that a mar ine teleost absorbs Fe2+ preferentially in the posterior intestine. This oc curs in spite of extremely high luminal bicarbonate concentrations recorded in vivo, which may be expected to reduce the bioavailability of divalent c ations as a result of the precipitation as carbonates (e.g. FeCO3).