Cyclic nucleotide phosphodiesterase type 5 activity limits blood flow to hypoperfused myocardium during exercise

Nitric oxide (NO) causes vasodilation by stimulation of guanylate cyclase in vascular smooth muscle to produce cGMP. The resultant vasodilator effect is regulated by a family of cGMP phosphodiesterases (PDEs). Sildenafil, a selective inhibitor of PDE5 used for treatment of erectile dysfunction, has been found to cause relaxation of isolated epicardial coronary artery segments. The present study examined the effects of sildenafil on coronary blood flow and hemodynamics during exercise in normal and ischemic heart.

In chronically instrumented normal dogs, sildenafil 2 mg/kg PO caused a slight but significant increase in left anterior descending (LAD) coronary blood flow during resting conditions, with a nonsignificant trend toward increased coronary flow during treadmill exercise. Exercise in the presence of LAD stenosis that decreased distal coronary pressure to 57+/-2 mm Hg reduced LAD flow during exercise from 69+/-8 to 41+/-7 mL/min (P:<0. 05), with hypoperfusion most severe in the subendocardium. At the same distal coronary pressure, sildenafil increased LAD flow in the ischemic region to 50+/-11 mL/min (P:<0.05). Increase in ischemic region blood flow produced by sildenafil was uniform across the LV wall, given that no change occurred in the transmural distribution of perfusion.

Inhibition of PDE5 with sildenafil caused vasodilation of coronary resistance vessels with an increase of blood flow into an ischemic myocardial region during exercise in the presence of coronary artery stenosis.