ERYTHRO-9-(2-HYDROXY-3-NONYL)ADENINE INHIBITS CYCLIC-3',5'-GUANOSINE MONOPHOSPHATE-STIMULATED PHOSPHODIESTERASE TO REVERSE HYPOXIC PULMONARY VASOCONSTRICTION IN THE PERFUSED RAT LUNG

Erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) was shown to reverse the h ypoxic presser response (HPR) in the isolated, blood-perfused rat lung model. EHNA, an adenosine deaminase inhibitor, showed reversal of the HPR in a dose-dependent manner (EC(50) = 129 +/- 30 mu M). We found t hat the reversal of HPR by EHNA was not mediated by the adenosine rece ptors because the EHNA effect was not blocked by the adenosine recepto r antagonist, 8-p-sulfophenyl-theophylline (67 mu M; n = 6), Pretreatm ent with a cy-clic-3',5'-adenosine monophosphate (cAMP)-dependent prot ein kinase inhibitor, Rp-adenosine-3',5'-cyclic monophosphorothioate 1 0.5 mM; n = 4), blocked EHNA reversal of the HPR. As an alternative me chanism of action, EHNA inhibition of cyclic nucleotide phosphodiester ase(s) isozymes was studied in endothelium intact and denuded pulmonar y arteries. Using anion-exchange chromatography the cyclic nucleotide phosphodiesterase (PDE) separated into predominantly PDE families 2 an d a mixture of 3 and 4. DEAF fractions showing cAMP hydrolysis activat ed by 5 mu M cyclic-3',5'-guanosine monophosphate (cGMP) had a K-m for cAMP of 6.3 mu M and an apparent K-act for cGMP of 1.4 mu M. EHNA was shown to inhibit PDE2 competitively. In intact vessels, the IC50 for EHNA was 3.3 mu M using 0.03 mu M [H-3]-cAMP substrate assayed in the presence of 2 mu M cGMP and in denuded vessels 3.7 mu M at 0.03 mu M [ 3H]-CAMP substrate in the presence of 5 mu M cGMP. Fractions in which cAMP hydrolysis was inhibited or not affected by 5 mu M cGMP (PDE3 and 4, respectively) showed an IC50 of >200 mu M for EHNA. We conclude th at reversal of the hypoxic presser response by EHNA in the isolated, p erfused rat lung model occurs with a mechanism involving in part inhib ition of smooth muscle PDE2.