Phosphodiesterase type 5 (
PDE5) inhibitors are used for treating
pulmonary arterial hypertension (PAH) in dogs. The long-acting
PDE5 inhibitor tadalafil was recently approved for treatment of PAH in humans. Basic information related to the pharmacological and hemodynamic effects of
tadalafil in dogs is scarce. In this study, the hemodynamic effects of
tadalafil after intravenous (IV) and
oral administration were investigated in a healthy vasoconstrictive PAH Beagle dog model induced by
U46619, a
thromboxane A2 mimetic. Six healthy Beagle dogs were anesthetized with
propofol and maintained with
isoflurane. Fluid-filled
catheters were placed into the descending aorta to measure systemic arterial pressure and in the pulmonary artery to measure pulmonary arterial pressure (PAP).
U46619 was infused via the cephalic vein to induce PAH. IV infusion of
U46619 significantly elevated PAP from baseline in a dose-dependent manner. U46619-elevated PAP and pulmonary vascular resistance was significantly attenuated by the simultaneous infusion of
tadalafil at 100 and 200 µg/kg/h. Likewise,
oral administration of
tadalafil at 1.0, 2.0, and 4.0 mg/kg significantly attenuated U46619-elevated PAP in a dose-dependent manner. U46619-elevated systolic and mean PAP decreased significantly 1 h after oral
tadalafil administration at 4.0 mg/kg, and this effect was maintained for 6 h. In conclusion,
tadalafil had a pharmacological effect in dogs and IV infusion of
tadalafil induced pulmonary arterial relaxation, while
oral administration of
tadalafil decreased PAP. These results suggest that
tadalafil may offer a new therapeutic option for treating dogs with PAH.