Comparison of oral and intraperitoneal iron supplementation in anaemic rats: a re-evaluation of the mucosal block theory of iron absorption.

To evaluate the extent to which daily oral Fe supplements may block Fe absorption from a subsequent dose, we compared effects of oral and intraperitoneal (i.p.) Fe supplementation on Fe status in anaemic rats (haemoglobin (Hb) 90 g/l). A ligated duodenal loop technique was used to assess the effects of the Fe supplements administered either orally or i.p. at different frequencies on Fe absorption from a subsequent test dose. Anaemic Sprague-Dawley rats were assigned to seven groups of eight rats each and received either oral or i.p. Fe supplements for 3 d as follows: (1) 4 mg oral supplement daily (three doses in 3 d); (2) 4 mg oral supplement once (one dose on day 1, low-Fe dose on days 2 and 3); (3) 12 mg oral supplement once (one dose on day 1, low-Fe dose on days 2 and 3); (4) 3.2 mg i.p. supplement daily (three doses in 3 d); (5) 3.2 mg i.p. supplement once (one dose on day 1); (6) 9.6 mg i.p. supplement once (one dose on day 1); (7) low-Fe diet (control). The effectiveness of the supplements in treating Fe deficiency on each of the two test-factors, i.e. route of administration and frequency of dose, was assessed by determining Hb-Fe gain and liver-Fe stores after the 3 d test period. Oral supplementation was as effective as i.p. in improving the Fe status of the anaemic animals. However, a 15 min absorption of a radio-Fe test dose from a ligated loop in i.p.-supplemented groups was significantly higher (11.68 (SD 1.70)%, 17.49 (SD 4.59)%, 16.71 (SD 3.39)%) than in orally supplemented groups (3.24 (SD 1.35)%, 2.45 (SD 1.05)%, 1.80 (SD 0.35)%) despite equal body Fe stores. No significant difference in intestinal Fe absorption efficiency was detected within the oral groups but those supplemented only once were more effective than or as effective as the group receiving daily supplements for 3 d in improving Fe status as indicated by Hb-regeneration efficiency. We conclude that there is a mucosal block with the administration of oral Fe supplements but the extent of this blocking effect during oral Fe supplementation is not as dramatic as currently thought in the context of the poor efficacy of daily Fe supplementation programmes.