title: Pulmonary vasoconstrictor influence of endothelin in exercising swine depends critically on phosphodiesterase 5 activity.
abstract: Both phosphodiesterase 5 (PDE5) inhibition and endothelin (ET) receptor blockade have been shown to induce pulmonary vasodilation. However, little is known about the effect of combined blockade of these two vasoconstrictor pathways. Since nitric oxide (NO) exerts its pulmonary vasodilator influence via production of cyclic guanosine monophosphate (cGMP) as well as through inhibition of ET, we hypothesized that interaction between the respective signaling pathways precludes an additive vasodilator effect. We tested this hypothesis in chronically instrumented swine exercising on a treadmill by comparing the vasodilator effect of the PDE5 inhibitor EMD360527, the ETA/ETB antagonist tezosentan, and combined EMD360527 and tezosentan. In the systemic circulation, vasodilation by tezosentan and EMD360527 was additive, both at rest and during exercise, resulting in a 17 ± 2% drop in blood pressure. In the pulmonary circulation, both EMD360527 and tezosentan produced vasodilation. However, tezosentan produced no additional pulmonary vasodilation in the presence of EMD360527, either at rest or during exercise. Moreover, in isolated preconstricted porcine pulmonary small arteries (∼300 μm) EMD360527 (1 nM-10 μM) induced dose-dependent vasodilation, whereas tezosentan (1 nM-10 μM) failed to elicit vasodilation irrespective of the presence of EMD360527. However, both PDE5 inhibition and 8Br-cGMP, but not 8Br-cAMP, blunted pulmonary small artery contraction to ET and its precursor Big ET in vitro. In conclusion, in healthy swine, either at rest or during exercise, PDE5 inhibition and the associated increase in cGMP produce pulmonary vasodilation that is mediated in part through inhibition of the ET pathway, thereby precluding an additional vasodilator effect of ETA/ETB receptor blockade in the presence of PDE5 inhibition.
authors.affiliation: Experimental Cardiology, Thoraxcenter, Erasmus MC, Univ. Medical Center Rotterdam, PO Box 2040, 3000 CA Rotterdam, The Netherlands. d.merkus@erasmusmc.nl.
authors.forename: Zhichao
authors.initials: Z
authors.lastname: Zhou
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: de Beer
authors.forename: Daphne
authors.initials: D
authors.lastname: de Wijs-Meijler
authors.forename: Shawn B
authors.initials: SB
authors.lastname: Bender
authors.forename: Maaike
authors.initials: M
authors.lastname: Hoekstra
authors.forename: M Harold
authors.initials: MH
authors.lastname: Laughlin
authors.forename: Dirk J
authors.initials: DJ
authors.lastname: Duncker
authors.forename: Daphne
authors.initials: D
authors.lastname: Merkus
mesh_terms: D000818:Animals; D006152:Cyclic GMP / Q000378:metabolism; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5 / Q000378:metabolism*; D004357:Drug Synergism; D065130:Endothelin A Receptor Antagonists; D065131:Endothelin B Receptor Antagonists; D016232:Endothelins / Q000037:antagonists & inhibitors / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D058986:Phosphodiesterase 5 Inhibitors / Q000494:pharmacology; D010805:Physical Conditioning, Animal / Q000502:physiology; D011652:Pulmonary Circulation / Q000187:drug effects / Q000502:physiology*; D011725:Pyridines / Q000494:pharmacology; D044022:Receptor, Endothelin A / Q000378:metabolism*; D044023:Receptor, Endothelin B / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D034421:Sus scrofa; D013777:Tetrazoles / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000494:pharmacology
chemical_list: D065130:Endothelin A Receptor Antagonists; D065131:Endothelin B Receptor Antagonists; D016232:Endothelins; D058986:Phosphodiesterase 5 Inhibitors; D011725:Pyridines; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D013777:Tetrazoles; D014662:Vasoconstrictor Agents; C120582:tezosentan; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D006152:Cyclic GMP
keywords: Big ET; ETA/ETB receptor blockade; PDE5 inhibition; exercise; pulmonary vascular tone