Tissue distribution of synthetic heme analogues: studies with tin, chromium, and zinc mesoporphyrins.

The uptake in tissue of Sn-mesoporphyrin (SnMP), Cr-mesoporphyrin (CrMP) and Zn-mesoporphyrin (ZnMP) administered at doses ranging from 1 to 10 mu mol/kg BW and the effects of these compounds on heme oxygenase activity were examined in both adult and neonatal rats. SnMP and CrMP, but not ZnMP, were rapidly cleared from blood and taken up by liver, spleen and kidney where marked inhibition of heme oxygenase activity was demonstrated. None of the metalloporphyrins were detectable in brain, and no inhibition of heme oxygenase activity was demonstrable in this tissue after administration of the compounds to both adult and neonatal rats. These results demonstrate that SnMP, CrMP and ZnMP do not cross the blood brain barrier, a fact of interest in relation to the potential use of these compounds clinically.