Ferrous sulphate does not directly affect pteroylmonoglutamic acid absorption in rats

Abstract

A variety of compounds which bind to Fe have substantial reductions in absorption when co-administered with Fe compounds. The binding of both Fe 2+ and Fe 3+ ions to pteroylmonoglutamic acid and the pteroylmonoglutamate dianion was examined in vitro . In dimethylsulphoxide (DMSO) alone, pteroylmonoglutamate formed a 2:1 (pteroylmonoglutamate: Fe 3+ ion) complex. However, in DMSO–aqueous Bis-Tris buffer (4:1, v/v; pH 6.0) no evidence of complex formation could be seen. Likewise spectroscopic evidence was obtained for complex formation with Fe 2+ ion and pteroylmonoglutamate in DMSO alone but not in the aqueous DMSO buffer. In vivo studies examined the effect of FeSO 4 on pteroylmonoglutamic acid absorption in an isolated perfused rat jejunal model of nutrient absorption. The dose of pteroylmonoglutamic acid approximated a human dose of 1 mg for the rat, while the FeSO 4 doses were chosen to represent 6.4 mg, 64 mg and 300 mg human doses. There was no significant effect of FeSO 4 on pteroylmonoglutamic acid absorption or instability of pteroylmonoglutamic acid in vivo in the presence of FeSO 4 in the rat. Although 2:1 binding of pteroylmonoglutamic acid to Fe ions could be demonstrated in DMSO alone, no binding could be demonstrated in DMSO–Bis-Tris buffer (4:1, v/v; pH 6.0). It is unlikely that there will be a significant reduction in pteroylmonoglutamic acid absorption during concurrent ingestion of Fe preparations.