Abstract

This study was conducted to evaluate the possibility of selective inhibition of either guanosine cyclic 3',5'-monophosphate or adenosine cyclic 3',5'-monophosphate phosphodiesterase activities of pig coronary arteries. Two peaks (I and II) of cyclic nucleotide phosphodiesterase activity and a heat-stable, nondialyzable activator of peak I can be resolved from the intima plus media layer of pig coronary arteries by DEAE-cellulose chromatography. Peak I catalyzes the hydrolysis of both cyclic GMP and cyclic AMP, but it has a much lower apparent K_m (1-4 µM) for cyclic GMP than for cyclic AMP (40-100 µM). Peak II activity is relatively specific for cyclic AMP and exhibits apparent negative cooperative behavior. Papaverine, 1-methyl-3-isobutylxanthine (MIX), 3',5'-cyclic nucleotides, and some 3',5'-cyclic nucleotide derivatives inhibit these phosphodiesterases to different degrees. For example, papaverine is 3-4 times more potent as an inhibitor of peak II than of peak I while MIX is 5-6 times more potent as an inhibitor of peak I than of peak II activity. Theophylline shows little selectivity for either form. The degree of inhibition of peak I by each agent is virtually independent of the cyclic nucleotide used as substrate. Hydrolysis of cyclic AMP by peak I activity is decreased by cyclic GMP more effectively than cyclic GMP hydrolysis is decreased by cyclic AMP. K_i values for inhibition of peak I activity by cyclic GMP and cyclic AMP correspond to their respective apparent K_m values. Cyclic GMP also inhibits the hydrolysis of cyclic AMP by peak II, and it is as effective as MIX in this regard. The effects of none of the above agents on peak I were altered by the presence or absence of heat-stable, nondialyzable activator. N²,2'-O-Dibutyryl cyclic GMP, 8-bromo cyclic GMP, and N⁶,2'-O-dibutyryl cyclic AMP are, in general, more potent than theophylline as inhibitors of both forms of phosphodiesterase. 8-Bromo cyclic GMP and dibutyryl cyclic GMP are about 10 times more potent as inhibitors of peak I activity with either substrate than of peak II activity, whereas dibutyryl cyclic AMP is about 10 times more potent as an inhibitor of peak II activity than of peak I activity. 8-Bromo cyclic GMP is 4-6 times more potent as an inhibitor of fully activated peak I with either substrate than of activator-deficient peak I activity, but effects of dibutyryl cyclic AMP or dibutyryl cyclic GMP are changed very little by the presence of the activator. These data suggest the possibility of selective pharmacological regulation of cyclic GMP or cyclic AMP levels through selective inhibition of coronary artery phosphodiesterase activities.