Am. J. Respir. Cell Mol. Biol.,
Volume 23, Number 2, August, 2000 222-227
Nitric Oxide (NO)-Dependent but Not NO-Independent Guanylate Cyclase
Activation Attenuates Hypoxic Vasoconstriction in Rabbit Lungs
Norbert
Weissmann,
Robert
Voswinckel,
André
Tadi ,*
Thorsten
Hardebusch,*
Hossein Ardeschir
Ghofrani,
Ralph Theo
Schermuly,
Werner
Seeger,
and
Friedrich
Grimminger
Department of Internal Medicine, Justus-Liebig-University Giessen, Giessen, Germany
Hypoxic pulmonary vasoconstriction (HPV) is essential for
matching lung perfusion with ventilation, thus optimizing
pulmonary gas exchange. Preceding studies provided evidence for a role of both nitric oxide (NO) and superoxide/
H2O2 formation in this vasoregulatory mechanism. Both agents
might be operative via stimulation of guanylate cyclase with
formation of the vasodilatory cyclic guanosine monophosphate (cGMP), the loss of which under conditions of hypoxia
contributes to HPV. This view is challenged by the recent suggestion of increased rather than decreased superoxide/H2O2 formation in hypoxia. We addressed the role of NO-dependent
versus NO-independent guanylate cyclase activity in hypoxic
and pharmacologically evoked vasoconstriction in perfused
rabbit lungs. Two inhibitors of soluble guanylate cyclase,
LY83583 (2 to 16 µM) and methylene blue (20 to 60 µM), increased baseline pulmonary artery pressure under normoxic
conditions and markedly amplified the vasoconstrictor response
to both hypoxia and the stable thromboxane analogue U46619. Under conditions of preblocked lung NO synthesis (NG-mono-methyl-L-arginine), however, additional guanylate cyclase inhibition further enhanced the vasoconstrictor response to U46619 but did not influence the strength of HPV. The selective phosphodiesterase V inhibitor Zaprinast (1 to 10 µM), used for prolongation of the cGMP half-life, reduced the hypoxia-induced
pressor response to a larger extent than the pressor response to
U46619. This difference was lost under conditions of preblocked
NO synthesis. Equilibration of the lung perfusate with molecular
NO suppressed the HPV more potently than the U46619-induced
vasoconstrictor response. We conclude that NO-dependent
guanylate cyclase activity has an important role in attenuating
the vasoconstrictor response to alveolar hypoxia in rabbit
lungs. In contrast, no evidence was obtained for a role of NO-independent cGMP formation in HPV. In this feature, HPV differs
from that elicited by the thromboxane analogue U46619.
*
Portions of the doctoral theses of these two authors are incorporated into
this report.
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Copyright © 2000 American Thoracic Society.
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