IN-VITRO AND IN-VIVO STUDIES OF DERIVATIVES OF 1,2-DIAZETINE AND NITRONYLNITROXIDE AS DONORS AND ACCEPTORS OF NITRIC-OXIDE

Various nitronylnitroxyl radicals (NNR) were studied as paramagnetic s cavengers of nitric oxide. The radicals react with NO with rate consta nts of (0.6-1.1)-10(4) M(-1). sec(-1), forming stable iminonitroxyl ra dicals.This can be used to measure nitric oxide in solutions by EPR sp ectroscopy, the sensitivity being 1 mu M for detection of NO and 0.3 n M/sec for measuring the NO generation rate in 1 h in a 0.2-ml sample. To overcome fast reduction of the radicals in biological samples, an N NR with a charged functional group was incorporated into the inner vol ume of large unilamellar phosphatidylcholine liposomes, decreasing the rates of NNR reduction by about 1000-fold. The approach was used to m easure the activity of NO synthase from rat cerebellum. NNR were used to study the decomposition of 3,4-dihydro-1,2-diazete 1,2-dioxides (DD ), supporting a previously proposed mechanism for DD decomposition wit h liberation of two mo- lecules of nitric oxide per DD molecule. The r ate constants for DD decomposition are in the range from 10(-8) to 6.5 . 10(-7) sec(-1) in water and from 3 . 10(-7) to 1.6 . 10(-5) sec(-1) in dimethylsulfoxide at 37 degrees C. Experiments with perfused rat t ail artery showed that some DD derivatives are highly effective vasodi lators at concentrations from 5 to 80 mu M Significant (up to 30%) dec rease in systolic arterial blood pressure was observed in genetically hypertensive rats (ISIAH-strain) when some DD were injected intraperit oneally (40-200 mu g/kg body weight), while the same effect of trinitr oglycerin (TNG) was found at much higher dose (900 mu g/kg).