Kinetics of Manganese Absorption in Ligated Small Intestinal Segments of Broilers

Two experiments were conducted with 28-day-old male commercial broilers to study mechanisms of Mn absorption and the effect of Mn treatment on divalent metal transporter 1 (DMT1) mRNA levels in ligated segments from different intestinal regions of broilers. The results from experiment 1 showed that the amount of Mn absorption was asymptotic with respect to time within 40 min after perfusion of the duodenal, jejunal, and ileal segments of broilers with 2.18 mmol/L of Mn as MnSO4. In experiment 2, a kinetic study of Mn absorption was performed with duodenal, jejunal, and ileal loops perfused with solutions containing 0, 0.13, 0.27, 0.54, 1.09, 2.18, 4.37, or 8.74 mmol/L of Mn as MnSO4. Manganese concentrations in perfusates were determined at 5 min after perfusion. In the control group and in the group treated with 2.18 mmol/L Mn as MnSO4, DMT1 mRNA levels of ligated intestinal regions at 30 min after perfusion were analyzed by real-time reverse transcription PCR. The kinetic curves of Mn absorption showed that Mn absorption was a carrier-mediated process in the duodenum and jejunum. The maximum absorption rate (J(max)) in duodenal segments was greater (P < 0.05) than that in the jejunum (94.08 vs. 81.17 nmol/cm per min). There was no significant difference (P = 0.85) in the Michaelis-Menten constant (K-m) values between the duodenum and jejunum (3.41 vs. 3.60 mmol/L). In the ileum of Mn-deficient broilers, the most probable mechanism of Mn absorption was a nonsaturable diffusion process, and the diffusive constant (P; means +/- SE) was 2.42 x 10(-2) +/- 5.22 x 10(-4) cm(2)/min. The DMT1 mRNA levels in the duodenum and jejunum of broilers were greater (P < 0.001) than the level in the ileum. The DMT1 mRNA level in the small intestine of broilers in the Mn treatment group decreased significantly (P < 0.001) compared with that of the control. The different mechanisms of Mn absorption found in different intestinal segments suggest that the ileum is the main site of Mn absorption in the small intestine of broilers.