ROLES OF cAMP AND cGMP IN THE SYNERGISTIC INHIBITORY EFFECTS OF NITROVASODILATORS AND PGE1 ON PLATELET AGGREGATION AND DEGRANULATION

D Maurice, R Haslam
1987 COAGULATION   unpublished
Washed rabbit platelets labelled with [14C]5-HT and suspended in a modified Tyrode's solution were used in this study. Incubation of the platelets with 0.1, 1 and 10 μM sodium nitro-prusside (SNP) for 30 s inhibited aggregation induced by 10 nM platelet-activating factor by 7, 13 and 45% and the release of [14C]5-HT by 16, 30 and 45%, respectively. In combination with 0.02 μM PGE1, which had little effect alone (7% inhibitions), these concentrations of SNP caused 58, 90 and 100% inhibitions of
more » ... 00% inhibitions of aggregation and 60, 73 and 81% inhibitions of [14C]5-HT release. Thus, SNP and PGE1 acted synergisti-cally. The changes in [3H]cGMP and [3H]cAMP caused by these compounds were measured in platelets labelled by preincubation with [3H]guanine and [3H]adenine. [3H]cGMP (initially 0.01% of platelet [3H]GTP) increased by amounts equivalent to 0.02, 0.10 and 0.63% of [3H]GTP with 0.1, 1 and 10 μM SNP. PGE1 had no effects on platelet [3H]cGMP. The above SNP concentrations also increased [3H]cAMP by amounts equivalent to 0.01, 0.02 and 0.04% of platelet [3H]ATP (basal value 0.02%). However, in the presence of 0.02 μM PGE1, 0.1, 1 and 10 μM SNP increased [3H]cAMP by amounts equivalent to 0.13, 0.26 and 0.39% of platelet [3H]ATP. Both with and without PGE1, 10 μM SIN-1 (the active metabolite of molsidomine) had effects similar to those of 1 μM SNP. Thus, the synergistic actions of PGE-, and SNP or SIN-1 on platelet function correlated with increases in [3H]cAMP, not [3H]cGMP. Preincubation of the platelets for 30 s with 200 μM 2∲,5∲-dideoxy-adenosine (an inhibitor of adenylate cyclase) reduced the above increases in [3H]cAMP and inhibitions of platelet reactions by about 60%, without affecting [3H]cGMP levels. Addition of specific inhibitors of platelet cAMP phosphodiesterase (e.g. cilostamide) enhanced the actions of PGE1 in a manner similar to SNP but had little effect on the actions of SNP. The results show that the nitrovasodilators studied have effects on platelet function and [3H]cAMP similar to those of inhibitors of cAMP phosphodiesterase, suggesting that their actions may be mediated by increases in cAMP caused by an effect of cGMP on the platelet cGMP-inhibited cAMP phosphodiesterase. (HSFO Grant T443H)
doi:10.1055/s-0038-1644533 fatcat:y533dplhyvh3rhu5eqcfkpwnm4