cGMP and cAMP cause pulmonary vasoconstriction in the presence of hemolysate

We recently reported that addition of a small amount of hemolysate to the s alt solution that perfused isolated rat lungs hypersensitized the vasculatu re to subsequent additions of ANG II or exposure to hypoxia, and addition o f NO gas ( NO) to the perfusate that contained hemolysate caused a strong v asoconstrictor rather than a vasodilator response. In the present study, we demonstrate that CO and the secondary messengers cGMP and cAMP (usually as sociated with vasodilation) exert similar effects in hemolysate-perfused lu ngs. Analogs of the cyclic nucleotides cGMP or cAMP (8-bromo-cGMP and dibut yryl-cAMP, respectively) caused profound vasoconstriction in the isolated r at lung perfused with a salt solution that contained hemolysate. The cGMP- or cAMP-analog-induced vasoconstriction was inhibited by chemically dissimi lar Ca2+ antagonists, by the protein phosphatase inhibitor okadaic acid, an d, to a lesser degree, by protein kinase inhibitor H-7. Antiphospho-threoni ne 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 va sodilatory stimuli, including analogs of cGMP and cAMP, with vasoconstricti on rather than vasodilation. The importance of our finding is the paradoxic al nature of the response to (analogs of) cyclic nucleotides because, to ou r knowledge, cyclic nucleotide-induced vasoconstriction has not been previo usly reported.