Studies of Iron Transport in Portal and Systemic Circulation

Simultaneous ⁵⁹Fe absorption curves in portal and systemic venous blood showed different rates of entry of the isotope into the portal (and systemic) circulation: the most rapid entry was seen in two patients with decreased iron stores, whereas negligible counts were obtained in two patients with increased iron stores. These data, combined with ⁵⁹Fe excretion data, indicate a barrier function of the intestinal mucosa for the passage of iron in two iron-sufficient patients, with evidence of prolonged excretion of ⁵⁹Fe into the bowel in one of these. The data support a two-step mechanism of absorption of inorganic ferrous iron in humans, the first step being uptake of iron by the intestinal mucosa; the second step transfer of mucosal iron to the portal circulation.

In the two patients with decreased iron stores the shape of the absorption curves ruled out significant hepatic deposition of isotope; the amount of isotope transported in the systemic circulation correlated closely with that utilized for hemoglobin synthesis.

Different rates of absorption of inorganic ferrous iron and folic acid were demonstrated in one patient.