Inhibition of separated forms of phosphodiesterases from pig coronary arteries by uracils and by 7-substituted derivatives of 1-methyl-3-isobutylxanthine

A series of 7-substituted 1-methyl-3-isobutylxanthines was designed in an attempt to increade the specificity of the 1-methyl-3-isobutylxanthine (MIX) structure for one of the two cyclic nucleotide phosphodiesterase peaks isolated by DEAE-cellulose chromatography of the soluble fraction of the intima + media layer of pig coronary arteries. A series of 1,3-dialkyluracils was of low potency as inhibitors of either peak I or peak II. The 7-substituted xanthines were prepared by alkylation of MIX with the corresponding alkyl or aralkyl halide in DMF containing K2CO3. These compounds were, in general, much less potent inhibitors of peak II activity than was MIX, but some of them retained the potency of MIX as inhibitors of peak I and, therefore, were relatively specific for inhibition of peak I. 7-Bzl-MIX was the most selective compound tested; it was a potent inhibitor of peak I activity but was much less effective as an inhibitor of peak II activity. Substitution of either electron-withdrawing (nitro) or electron-donating (methoxy) groups on the 7-benzyl moiety reduced the effectiveness of the 7-benzyl compounds as inhibitors of peak I. Chlorobenzyl substitution increased the potency slightly over the benzyl but not the selectivity between peaks.

Cyclic nucleotide phosphodiesterase activities of pig coronary arteries

Most (85% or more) of the cyclic nucleotide phosphodiesterase (3' :5' -cyclic-AMP 5'-nucleotidohydrolase, EC 3.1.4.17) activity of pig coronary arteries was found in the 40 000 times g supernatant fraction of homogenates of the intima plus media layer. Chromatography of the soluble fraction of this layer on DEAE-cellulose resolved two phosphodiesterase activities and a heat stable, non-dializable activator. Peak I activity had apparent Km values of 2-4 muM for cyclic GMP and 40-100 muM for cyclic AMP. Peak II activity was relatively specific for cyclic AMP and exhibited apparent negatively cooperative behavior. Peak I but not peak II activity could be stimulated 3-8-fold by the addition of the boiled activator fraction or a boiled crude supernatant fraction. Cyclic AMP hydrolysis by peak I or peak II was more rapid in the presence of Mn-2+ than Mg-2+, but the latter promoted hydrolysis of cyclic GMP by peak I more effectively than did Mn-2+ in the presence of activator. In the absence of added metals, ethylene bis(oxyethylenenitriol)tetra-acetic acid (EGTA) and EDTA both inhibited hydrolysis of cyclic AMP and cyclic GMP by phosphodiesterase activities in the supernatant fraction and in peak I, but EDTA produced more complete inhibition at lower concentrations than did EGTA. Imidazole (1 muM to 10 mM) had virtually no effect on the hydrolysis of cyclic AMP or cyclic GMP catalyzed by either of the two separated peaks or by total phosphodiesterase activities in crude supernatant or particulate fractions.