Nitric oxide modulates the frog heart ventricle morphodynamics

The aim of this work was to investigate in the avascular heart of the frog Rana esculenta the influence of nitricoxide (NO) on ventricular systolic and diastolic functions by using a novel image analysis technique. Theexternal volume variations of the whole ventricle were monitored during the heart cycle by video acquisition(visible light) and analysed by an appropriately developed software with a specific formula for irregularconvex solids. The system, which measures the rate of volume changes and the ejection fraction, directlydetermined the volumetric behaviour of the working frog heart after stimulation or inhibition of NOS-NOcGMPpathway. End-diastolic volume (EDVext), end-systolic volume (ESVext), contraction and relaxationvelocities (dV/dtsys and dV/dtdia, respectively), stroke volume (SV) and ejection fraction (EF), were measuredbefore and after perfusion with NOS substrate (L-arginine), NO donor (SIN-1), cGMP analogue (8-Br-cGMP),NOS inhibitors (NG-monomethyl-L-arginine, L-NMMA; L-N(5)-(1-iminoethyl)-ornithine, L-NIO; 7-Nitroindazole,7-NI) and guanylyl cyclase inhibitor (ODQ). The results showed that NO reduces ventricular systolicfunction improving diastolic filling, while NOS inhibition increases contractility impairing ventricular fillingcapacity. The presence of activated eNOS (p-eNOS) was morphologically documented, further supporting thatthe mechanical activity of the ventricular pump in frog is influenced by a tonic release of NOS-generated NO.