Norbormide (NRB, see Figure 1A for structure) is a unique vasoactive compound endowed with species-specific vasoconstrictor activity that targets the peripheral blood vessels of the rat (Clarke, 1965; Roszkowski, 1965; Bova et al., 1996). It also provokes a vasorelaxant effect on arteries of several non-rat species, as well as on rat large-caliber vessels (Roszkowski, 1965; Poos et al., 1966; Cavalli et al., 2004). NRB is a mixture of up to eight stereoisomers, four endo-isomers and four exo-isomers; among them, only the endo-isomers demonstrate vasocontractile and rat toxicant activities (Poos et al., 1966), whereas both endo- and exo-isomers have vasodilatatory activity in rat aorta and in non-rat arteries (Cavalli et al., 2004). The contractile effect of NRB on rat peripheral blood vessels is endothelium-independent, and is of myogenic nature as confirmed by its action on single rat caudal artery myocytes (Fusi et al., 2002; Cavalli et al., 2004). NRB binding sites and the molecular mechanisms involved in its biological effects in vascular tissue have yet to be fully characterized; it has been proposed that NRB-induced vasoconstriction may result from an interaction with a phospholipase C-coupled receptor (Bova et al., 2001), whereas its relaxant effect may be caused by an inhibitory action on plasma membrane voltage-dependent L-type Ca2+ channels (Fusi et al., 2002). NRB has also been shown to activate the mitochondrial permeability transition pore (mPTP) in isolated rat mitochondria, but not in mitochondria obtained from either guinea-pigs or mice. This suggests that the effect on the mPTP, like NRB-vasoconstriction, is also species-specific. However, since this effect could also be induced in mitochondria isolated from different organs of the rat (Ricchelli et al., 2005; Zulian et al., 2007, 2011), unlike vasoconstriction, mPTP activation is not tissue-specific. It is therefore unclear whether NRB-induced activation of the mPTP constitutes a role in the vasoconstrictor effect of NRB.