Effect of 4-aminopyrazolopyrimidine on rabbit plasma cholesterol, platelet 3-hydroxy-3-methyl-glutary L-coenzyme A reductase and platelet aggregation

The effect of 4-aminopyrazolo(3,4-d) pyrimidine on mouse plasma alpha-amylase activity

A single dose of 4-aminopyrazolo(3,4-d) pyrimidine (4APP), an adenine analog, was orally administered at various concentrations of groups of mice and after 24 h, the plasma-alpha-amylase activity and cholesterol levels had significantly decreased in a dose-dependent manner. There was no change, however, in pancreatic superoxide dismutase activity or the lipid peroxide level. Histologically, zymogen degranulation was found after a high oral dose of 4APP (175 mg/kg). The same decrease in alpha-amylase activity occurred in mice that had received ip administration of 4APP, and in mice that were pretreated with dimethyl sulfoxide. Based on these results, it appears that 4APP decreases plasma alpha-amylase activity dose-dependently, possibly by pancreatic injury, and that free radicals play no part in the observed changes.

Beclobrinic acid--a new hypolipidemic agent--inhibits in vitro human platelet activation by blocking prostaglandin synthesis

Effects and the mechanism of the antiplatelet actions of beclobrinic acid, free acid form of a new hypolipidemic agent beclobrate [(+)-2-[d-(P-chlorophenyl)p-tolyl)oxy)-2-methyl-butyrate), were examined using human platelets. Platelet-rich plasma (PRP) which has been prelabeled with (14C)-serotonin was incubated with beclobrinic acid (BBA) for one minute before the addition of various agonists. BBA (0.1-1.5 mM) inhibited platelet aggregation and serotonin secretion induced by ADP, epinephrine, arachidonic acid and collagen in a concentration dependent manner. BBA also inhibited arachidonic acid-induced production of malondialdehyde (MDA), a byproduct of prostaglandins, in a concentration dependent manner. However, up to 1.0 mM BBA did not inhibit platelet aggregation induced by U46619, a stable analog of prostaglandin H2. In other experiments BBA also blocked thrombin-induced release of (3H)-arachidonic acid from platelet phospholipids. These findings suggest that: (a) BBA inhibits platelet aggregation and serotonin secretion by inhibiting prostaglandin synthesis at two steps. First by interfering in the release of arachidonic acid from platelet phospholipids and second by inhibiting its conversion into prostaglandins; and (b) BBA does not inhibit the action of prostaglandins on human platelets.