Five 1-oximino-1-nitro compounds (nitrolic acids) were prepared and tested for antithrombotic and blood pressure lowering activities. 1-Nitro-ethanone 1-oxime (1, ethylnitrolic acid) 2 h after oral administration to rats inhibited thrombus formation by a laser beam in mesenteric arterioles of rats by 69% and by 46% in venules (60 mg/kg). The blood pressure of SHR rats even at this high dose only was decreased by 10% suggesting that antithrombotic and blood pressure effects can be dissociated. The in vitro decomposition of 1 at 37 degrees C nearly exclusively gave N2O and acetic acid indicating that HNO primarily had been formed.
Five 1,3,4-triazol-1-oles (5a-f) with different alkyl, aryl, and arylalkyl substituents in 2,5-position were synthesized and tested for their antithrombotic properties. The 2,5-dimethyl derivative 5a was most active. 2 h after administration of 60 mg/kg to rats thrombus formation by a laser beam was inhibited by 42% in arterioles and by 33% in venules. At the same dose the blood pressure of SHR rats was slightly (5%) but significantly decreased even 4 h after application of 5a. This pattern of activities suggests a nitric oxide mediated mechanism of action. 1,1'-Azo-bis-ethanone oxime(7)-the synthetic precursor of 5a-inhibited the aggregation of blood platelet (Born test) with an IC50 = 15 mumol/L.
Oligosydnone imines are strongly bound to albumin (alpha < 1%) in pure water. In saline, however, this effect is abolished (alpha approximately 80%). 4,4'-Propylene-bis-3-hexyl-sydnone-5-imine hydrochloride (1) moderately binds to phosphatidylcholine liposomes (PC, alpha approximately 34%). This is increased by phosphatidylethanolamine (PE). In PC/PE vesicles alpha is about 7%. The binding is further enhanced by the incorporation of negatively charged phospholipids (PL) like phosphatidylserine (PS). In PC/PE/PS liposomes complete binding of 1 can be achieved. This holds especially true if the composition of the liposomes is similar to the PL composition of platelet membranes. The results suggest that the antiplatelet activity of 1 is mediated by the bindings to negatively charged PL in the platelet membrane.
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