We reported previously that plasma levels, urinary excretion, and metabolic production of cyclic guanosine 3',5'-monophosphate (cGMP) are increased in gravid rats, and postulated that endogenous nitric oxide (NO), a potent vasodilator and immune modulator, may mediate this change. Four lines of evidence are now presented demonstrating increased biosynthesis of NO during pregnancy in rats: 1) Urinary excretion and plasma levels of the stable NO metabolite, nitrate, are elevated in pregnant rats; urinary excretion of nitrate is increased in pseudopregnant rats. 2) The urinary excretion of cGMP also increases during pregnancy and pseudopregnancy, paralleling the rise in urinary nitrate excretion. 3) Chronic treatment with the NO synthase inhibitor, NG-nitroarginine methyl ester (NAME), inhibits the increase in urinary nitrate excretion. 4) Nitric oxide hemoglobin is detected by electron paramagnetic resonance spectroscopy in the blood of pregnant, but not in nonpregnant, rats. The results show endogenous NO production is increased in gravid rats. This finding raises the possibility that NO may contribute to maternal vasodilation and uterine immune suppression of normal pregnancy.

Colorimetric (near-UV absorption spectroscopy) and calorimetric (isothermal titration calorimetry) methods have been used to quantify the equilibrium and thermodynamics of arsenite and monomethylarsenite (MMA) coordinating to glutathione (GSH) and the dithiols dimercaptosuccinic acid (DMSA), dihydrolipoic acid (DHLA), and dithiothreitol (DTT). We found that both arsenite and MMA form moderately stable complexes (beta = 10(6)-10(7)) with GSH; that arsenite forms a particularly stable 2:3 complex (beta approximately 10(18)) with the biological cofactor DHLA; that MMA has a somewhat higher affinity than arsenite for thiol ligands; and that entropic factors modulate the overall stability of As(III) complexes with thiols, which are favored by the exothermic formation of As(III)-thiolate bonds. The implications of these results for arsenic toxicity are discussed.

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We describe a simple method for measuring sodium azide concentrations in aliquots of blood and other tissues. Aliquots are acidified, converting azide to volatile hydrazoic acid (HN3) which is then trapped in sodium hydroxide. We analyze the resulting aliquots by ion chromatography, using a sodium tetraborate eluent and suppressed conductivity detection. The method is sensitive to at least 100 ng/mL.

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