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1 Pulmonary Hypertension Center, 2 Department of Pathology, and 3 Division of Renal Diseases and Hypertension, University of Colorado Medical School, Denver, Colorado 20262
We recently reported that addition of a small
amount of hemolysate to the salt solution that perfused isolated rat
lungs hypersensitized the vasculature to subsequent additions of ANG II
or exposure to hypoxia, and addition of NO gas (· NO) to the
perfusate that contained hemolysate caused a strong vasoconstrictor
rather than a vasodilator response. In the present study, we
demonstrate that CO and the secondary messengers cGMP and cAMP (usually
associated with vasodilation) exert similar effects in
hemolysate-perfused lungs. Analogs of the cyclic nucleotides cGMP or
cAMP (8-bromo-cGMP and dibutyryl-cAMP, respectively) caused profound
vasoconstriction in the isolated rat lung perfused with a salt solution
that contained hemolysate. The cGMP- or cAMP-analog-induced
vasoconstriction was inhibited by chemically dissimilar
Ca2+ antagonists, by the protein
phosphatase inhibitor okadaic acid, and, to a lesser degree, by protein
kinase inhibitor H-7. Antiphosphothreonine immunoblotting demonstrated
that lungs perfused with hemolysate exhibit increased phosphorylation
of several proteins. These data indicate that, in the presence of
hemolysate, pulmonary vasculature responds to nominally vasodilatory
stimuli, including analogs of cGMP and cAMP, with vasoconstriction
rather than vasodilation. The importance of our finding is the
paradoxical nature of the response to (analogs of) cyclic nucleotides
because, to our knowledge, cyclic nucleotide-induced vasoconstriction
has not been previously reported.
nitric oxide; carbon monoxide; calcium antagonists; hypersensitization
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