A NEW CLASS OF FUROXAN DERIVATIVES AS NO DONORS - MECHANISM OF ACTION AND BIOLOGICAL-ACTIVITY

1 The mechanism of action and biological activity of a series of R-substituted and di-R-substituted phenylfuroxans is reported. 2 Maximal potency as vasodilators on rabbit aortic rings, precontracted with noradrenaline (1 mu M), was shown by phenyl-cyano isomers and by the 3,4-dicyanofuroxan, characterized by a potency ratio 3-10 fold higher than glyceryl trinitrate (GTN). This effect was reduced upon coincubation with methylene blue or oxyhaemoglobin (10 mu M). 3 The furoxan derivatives showing maximal potency as vasodilators were also able to inhibit collagen-induced platelet aggregation, with IC50 values in the sub-micromolar range. 4 The furoxan derivatives were able to stimulate partially purified, rat lung soluble guanylate cyclase; among the most active compounds, the 3-R-substituted isomers displayed a higher level of stimulatory effect than the 4-R analogues. 5 Solutions (0.1 mM) of all the tested furoxans, prepared using 50 mM phosphate buffer, pH 7.4, (diluting 10 mM DMSO stock solutions) did not release nitric oxide (NO) spontaneously; however in presence of 5 mM L-cysteine, a significant NO-releasing capacity was observed, which correlated significantly with their stimulation of the guanylate cyclase activity.