Possible novel mechanism for bitter taste mediated through cGMP.
(1/668)
Taste is the least understood among sensory systems, and bitter taste mechanisms pose a special challenge because they are elicited by a large variety of compounds. We studied bitter taste signal transduction with the quench-flow method and monitored the rapid kinetics of the second messenger guanosine 3',5'-cyclic monophosphate (cGMP) production and degradation in mouse taste tissue. In response to the bitter stimulants, caffeine and theophylline but not strychnine or denatonium cGMP levels demonstrated a rapid and transient increase that peaked at 50 ms and gradually declined throughout the following 4.5 s. The theophylline- and caffeine-induced effect was rapid, transient, concentration dependent and gustatory tissue-specific. The effect could be partially suppressed in the presence of the soluble guanylyl cyclase (GC) inhibitor 10 microM ODQ and 30 microM methylene blue but not 50 microM LY 83583 and boosted by nitric oxide donors 25 microM NOR-3 or 100 microM sodium nitroprusside. The proposed mechanism for this novel cGMP-mediated bitter taste signal transduction is cGMP production partially by the soluble GC and caffeine-induced inhibition of one or several phosphodiesterases. (+info)
Reaction of organic nitrate esters and S-nitrosothiols with reduced flavins: a possible mechanism of bioactivation.
(2/668)
Organic nitrate esters, such as glyceryl trinitrate and isosorbide dinitrate, are a class of compounds used to treat a variety of vascular ailments. Their effectiveness relies on their ability to be bioactivated to nitric oxide (NO) which, in turn, relaxes vascular smooth muscle. Although there have been many biological studies that indicate that NO can be formed from organic nitrate esters in a biological environment, the chemical mechanism by which this occurs has yet to be established. Previous studies have implicated both flavins and thiols in organic nitrate ester bioactivation. Thus, we examined the chemical interactions of flavins and thiols with organic nitrate esters as a means of determining the role these species may play in NO production. Based on these studies we concluded that a reasonable chemical mechanism for organic nitrate ester bioactivation involves reduction to the organic nitrite ester followed by conversion to a nitrosothiol. The release of NO from nitrosothiols can occur via a variety of processes including reaction with dihydroflavins and NADH. (+info)
In vivo effects of new inhibitors of catechol-O-methyl transferase.
(3/668)
1. The effects of two new synthetic compounds showing in vitro catechol-O-methyl transferase (COMT) inhibitor properties were studied in vivo and compared with the effects of nitecapone and Ro-41-0960. 2. QO IA (3-(3-hydroxy-4-methoxy-5-nitrobenzylidene)-2,4-pentanedione), QO IIR ([2-(3,4-dihydroxy-2-nitrophenyl)vinyl]phenyl ketone), nitecapone and Ro-41-0960 (30 mg kg(-1), i.p.) were given to reserpinized rats 1 h before the administration of L-DOPA/carbidopa (LD/CD, 50:50 mg kg(-1), i.p.). Locomotor activity was assessed 1 h later. All the COMT inhibitors (COMTI), with the exception of QO IA, markedly potentiated LD/CD reversal of reserpine-induced akinesia. Similar results were obtained when the COMTI were coadministered with LD/CD. The effect of compound QO IIR was dose-dependent (7.5-30 mg kg(-1), i.p.). 3. The COMTI (30 mg kg(-1), i.p.) potentiated LD/CD reversal of both catalepsy and hypothermia of reserpinized mice. 4. QO IIR, nitecapone and Ro-41-0960 (30 mg kg(-1), i.p.) reduced striatal 3-methyl-DOPA (3-OMD) levels and increased dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) levels. Compound QO IA was devoid of any effect on striatal amine levels. In contrast to the other inhibitors, Ro-41-0961 reduced HVA levels as well. The effect of QO IIR on striatal amine levels was dose-dependent (7.5-60 mg kg(-1), i.p.) 5. These results suggest that the new compound QO IIR is an effective peripherally acting COMT inhibitor in vivo. (+info)
Chemoselective nitro group reduction and reductive dechlorination initiate degradation of 2-chloro-5-nitrophenol by Ralstonia eutropha JMP134.
(4/668)
Ralstonia eutropha JMP134 utilizes 2-chloro-5-nitrophenol as a sole source of nitrogen, carbon, and energy. The initial steps for degradation of 2-chloro-5-nitrophenol are analogous to those of 3-nitrophenol degradation in R. eutropha JMP134. 2-Chloro-5-nitrophenol is initially reduced to 2-chloro-5-hydroxylaminophenol, which is subject to an enzymatic Bamberger rearrangement yielding 2-amino-5-chlorohydroquinone. The chlorine of 2-amino-5-chlorohydroquinone is removed by a reductive mechanism, and aminohydroquinone is formed. 2-Chloro-5-nitrophenol and 3-nitrophenol induce the expression of 3-nitrophenol nitroreductase, of 3-hydroxylaminophenol mutase, and of the dechlorinating activity. 3-Nitrophenol nitroreductase catalyzes chemoselective reduction of aromatic nitro groups to hydroxylamino groups in the presence of NADPH. 3-Nitrophenol nitroreductase is active with a variety of mono-, di-, and trinitroaromatic compounds, demonstrating a relaxed substrate specificity of the enzyme. Nitrosobenzene serves as a substrate for the enzyme and is converted faster than nitrobenzene. (+info)
Primary hypoxic tolerance and chemical preconditioning during estrus cycle in mice.
(5/668)
BACKGROUND AND PURPOSE: Exogenous application of estrogens or progesterone ameliorates hypoxic/ischemic cell damage. This study investigates whether values of primary and induced hypoxic tolerance vary endogenously during the estrus cycle in female mice. METHODS: Population spike amplitude (PSA) and NADH were measured during hypoxic hypoxia and recovery in hippocampal slices from untreated control animals (C slices) and slices prepared from animals pretreated in vivo with a single intraperitoneal injection of 3-nitropropionate (3NP) (3NP slices) or acetylsalicylate (ASA) (ASA slices). RESULTS: Posthypoxic recovery of PSA was dose dependent in 3NP slices from males, with maximal recovery on pretreatment attained with 20 mg/kg 3NP (82+/-32% [mean+/-SD]; C slices, 38+/-29%; P<0.01). PSA recovered to 17+/-12% in C slices during proestrus, 43+/-23% during estrus, and 63+/-44% during diestrus. In 3NP slices, recovery of PSA increased to 57+/-36% (P<0. 05) during proestrus. Hypoxic tolerance was not increased in other stages of the estrus cycle. Hypoxic NADH increase during proestrus declined from 212+/-76% in C slices to 133+/-11% in 3NP slices (P<0. 05). Recovery of PSA in ASA slices was 75+/-36% (P<0.01 versus control) in males and 48+/-34% during proestrus (P<0.05 versus ASA slices from males). CONCLUSIONS: Primary and induced hypoxic tolerance are endogenously modulated during the estrus cycle. Differences in hypoxic oxidative energy metabolism mediate part of the differential tolerance. Experimental and clinical therapeutic strategies against cerebral ischemia/hypoxia need to consider sex-related dependence. (+info)
Vasoconstrictors and nitrovasodilators reciprocally regulate the Na+-K+-2Cl- cotransporter in rat aorta.
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Little is known about the function and regulation of the Na+-K+-2Cl- cotransporter NKCC1 in vascular smooth muscle. The activity of NKCC1 was measured as the bumetanide-sensitive efflux of 86Rb+ from intact smooth muscle of the rat aorta. Hypertonic shrinkage (440 mosmol/kgH2O) rapidly doubled cotransporter activity, consistent with its volume-regulatory function. NKCC1 was also acutely activated by the vasoconstrictors ANG II (52%), phenylephrine (50%), endothelin (53%), and 30 mM KCl (54%). Both nitric oxide and nitroprusside inhibited basal NKCC1 activity (39 and 34%, respectively), and nitroprusside completely reversed the stimulation by phenylephrine. The phosphorylation of NKCC1 was increased by hypertonic shrinkage, phenylephrine, and KCl and was reduced by nitroprusside. The inhibition of NKCC1 significantly reduced the contraction of rat aorta induced by phenylephrine (63% at 10 nM, 26% at 30 nM) but not by KCl. We conclude that the Na+-K+-2Cl- cotransporter in vascular smooth muscle is reciprocally regulated by vasoconstrictors and nitrovasodilators and contributes to smooth muscle contraction, indicating that alterations in NKCC1 could influence vascular smooth muscle tone in vivo. (+info)
Minor structural changes in nicotinoid insecticides confer differential subtype selectivity for mammalian nicotinic acetylcholine receptors.
(7/668)
The major nitroimine insecticide imidacloprid (IMI) and the nicotinic analgesics epibatidine and ABT-594 contain the 6-chloro-3-pyridinyl moiety important for high activity and/or selectivity. ABT-594 has considerable nicotinic acetylcholine receptor (AChR) subtype specificity which might carry over to the chloropyridinyl insecticides. This study considers nine IMI analogues for selectivity in binding to immuno-isolated alpha1, alpha3 and alpha7 containing nicotinic AChRs and to purported alpha4beta2 nicotinic AChRs. Alpha1- and alpha3-containing nicotinic AChRs (both immuno-isolated by mAb 35, from Torpedo and human neuroblastoma SH-SY5Y cells, respectively) are between two and four times more sensitive to DN-IMI than to (-)-nicotine. With immuno-isolated alpha3 nicotinic AChRs, the tetrahydropyrimidine analogues of IMI with imine or nitromethylene substituents are 3-4 fold less active than (-)-nicotine. The structure-activity profile with alpha3 nicotinic AChRs from binding assays is faithfully reproduced in agonist potency as induction of 86rubidium ion efflux in intact cells. Alpha7-containing nicotinic AChRs of SH-SY5Y cells (immuno-isolated by mAb 306) and rat brain membranes show maximum sensitivity to the tetrahydropyrimidine analogue of IMI with the nitromethylene substituent. The purported alpha4beta2 nicotinic AChRs [mouse (Chao & Casida, 1997) and rat brain] are similar in sensitivity to DN-IMI, the tetrahydropyrimidine nitromethylene and nicotine. The commercial insecticides (IMI, acetamiprid and nitenpyram) have low to moderate potency at the alpha3 and purported alpha4beta2 nicotinic AChRs and are essentially inactive at alpha1 and alpha7 nicotinic AChRs. In conclusion, the toxicity of the analogues and metabolites of nicotinoid insecticides in mammals may involve action at multiple receptor subtypes with selectivity conferred by minor structural changes. (+info)
Nitric oxide can function as either a killer molecule or an antiapoptotic effector in cardiomyocytes.
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Caspase enzymes are a family of cysteine proteases that play a central role in apoptosis. Recently, it has been demonstrated that caspases can be S-nitrosylated and inhibited by nitric oxide (NO). The present report shows that in chick embryo heart cells (CEHC), NO donor molecules such as S-nitroso-N-acetylpenicillamine (SNAP), S-nitrosoglutathione, spermine-NO or sodium nitroprusside inhibit caspase activity in both basal and staurosporine-treated cells. However, the inhibitory effect of NO donors on caspase activity is accompanied by a parallel cytotoxic effect, that precludes NO to exert its antiapoptotic capability. N-Acetylcysteine (NAC) at a concentration of 10 mM blocks depletion of cellular glutathione and cell death in SNAP-treated CEHC, but it poorly affects the ability of SNAP to inhibit caspase activity. Consequently, in the presence of NAC, SNAP attenuates not only caspase activity but also cell death of staurosporine-treated CEHC. These data show that changes in the redox environment may inhibit NO-mediated toxicity, without affecting the antiapoptotic capability of NO, mediated by inhibition of caspase enzymes. NO may thus be transformed from a killer molecule into an antiapoptotic agent. (+info)