Recently, a third endogenous gaseous signaling molecule, hydrogen sulfide (H₂S), has emerged as an important mediator of cardiovascular homeostasis, with biochemical properties similar to carbon monoxide and nitric oxide. The role of H₂S in the mammalian cardiovascular system is well documented. In rat, H₂S induces a dose-dependent relaxation of arteries and veins in vitro, a reduction of blood pressure in vivo and a negative inotropism in perfused hearts (Geng et al., 2004, Biochem. Biophys. Res. Commun. 313: 362–368).

In non mammalian vertebrates, vasoactive properties of H₂S have been also demonstrated in at least one species from each class of vertebrates (Dombkowski et al., 2005, Am. J. Physiol. 288: R243–R252). In contrast, nothing is known about the cardiac effects of H₂S in non mammalian vertebrates.

The purpose of the present study was to assess the effects of H2S on the avascular heart of the frog Rana esculenta. Perfusion of isolated heart with a donor of H₂S, sodium hydrosulfide (NaHS; 10^­11–10^­7M) significantly reduced the stroke volume (used as index of inotropism) in a concentration-dependent manner. This effect involved KATP channels while appeared independent from NOS-cGMP pathway.

Our preliminary data support the hypothesis that H₂S may represent a phylogenetically ancient cardioactive molecule. Studies are in progress to examine the mechanism of action involved in the cardiac action of H₂S.