This study investigated genotype- and tissue-related differences in the biodistribution of superparamagnetic magnetite (Fe3O4) nanoparticles (IONs) into the heart and liver of normotensive Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats after a single i.v. infusion of polyethylene glycol-coated IONs (~30 nm, 1mg Fe/kg) 100 min post-infusion. The effects of IONs on the expression of selected genes involved in the regulation of iron metabolism, includingNos,SodandGpx4, and their possible regulation by nuclear factor (erythroid-derived 2)-like 2 (NRF2, encoded byNfe2l2) and iron-regulatory protein (encoded byIrp1) were investigated. In addition, superoxide and nitric oxide (NO) production were determined. Results showed reduced ION incorporations into tissues of SHR compared to WKY and in the hearts compared to the livers. IONs reduced plasma corticosterone levels and NO production in the livers of SHR. Elevated superoxide production was found only in ION-treated WKY. Results also showed differences in the regulation of iron metabolism on the gene level in the heart and liver. In the hearts, gene expressions ofNos2,Nos3,Sod1,Sod2,Fpn,Tf,Dmt1andFth1correlated withIrp1but not withNfe2l2,suggesting that their expression is regulated by mainly iron content. In the livers, expressions ofNos2,Nos3,Sod2,Gpx4, andDmt1correlated withNfe2l2but not withIrp1, suggesting a predominant effect of oxidative stress and/or NO.