LAUSR

The novel peptide dwarf open reading frame (DWORF), highly conserved across species and expressed almost exclusively in cardiac ventricular muscle, may play a role in cardiac physiology and pathophysiology. The effect of direct administration of DWORF in the intact heart has not previously been examined. Accordingly, we investigated the cardiac effects of DWORF (1-30 nM) in normal isolated perfused rat hearts and hearts undergoing ischaemia/reperfusion (I/R) injury, and evaluated potential mechanisms of action. Exogenous DWORF at the top dose (30 nM) increased perfusion pressure (PP) in normal hearts, which indicates coronary vasoconstriction; and during post-ischaemic reperfusion, DWORF increased PP in a dose-dependent manner. In I/R hearts, DWORF at the top dose also increased left ventricular end-diastolic pressure and maximum and minimum derivatives of left ventricular pressure noted dP/dt(max) and dP/dt(min) respectively, without affecting developed pressure (DP). Co-infusion of DWORF with Diltiazem, an L-type Ca2+ channel blocker (1µM), in I/R hearts attenuated the falls in DP, dP/dt(max) and dP/dt(min) observed with Diltiazem alone. DWORF co-infusion with both Diltiazem and Y27632 (1µM) (a Rho-Kinase inhibitor) reversed the coronary vasodilator effect of the inhibitors administered alone. In conclusion, we provide the first evidence that DWORF has coronary vasoconstrictor actions in normal hearts and when administered during reperfusion in an ex-vivo model of cardiac I/R injury, and also exhibits positive cardiac inotropic activity in the latter setting. DWORF's effect on ventricular contractile function appears to be dependent on the L-type Ca2+ channel, whereas Rho-Kinase activity may be related to the coronary vasoconstrictor effects of DWORF.