nitroarginine and 1-1-diethyl-2-hydroxy-2-nitrosohydrazine

During maturation the vascular system undergoes structural and functional remodeling. At the systemic level it results in a gradual increase of arterial blood pressure during postnatal ontogenesis. The mechanisms of maintaining the blood pressure at a comparatively low level during the early postnatal development are not completely understood. Recently we showed that the hindlimb arteries of young (1-2 wk-old) rats exhibited an enhanced endothelial NO-pathway activity, which weakened their contractile responsiveness compared to the arteries of adult rats. Here we tested the hypothesis that an increased tonic endothelial NO production can take place in the whole vascular system leading to a decreased level of systemic blood pressure in young rats.. Segments of small mesenteric, saphenous, sural and intrarenal arteries were isolated from the young (2 wk-old), juvenile (4 wk-old) and adult (10-12 wk-old) male rats and tested in a wire isometric myograph. Anticontractile effect of NO was evaluated by the effects of NOS inhibitor L-NNA on both arterial spontaneous tone and constrictor responses to methoxamine (α1-adrenoceptor agonist). In addition, eNOS and arginase-2 mRNA expression in arterial preparations by qPCR and serum nitrite/nitrate levels by Griess reaction were estimated. Blood pressure with an intra-carotid artery catheter was measured in conscious rats.. In all arteries of 2 wk rats except the renal ones, L-NNA exposure resulted in a considerable tonic contraction and a remarkable enhancement of contractile responses to methoxamine. The effect of L-NNA gradually decreased with age and by 10-12 weeks became very small in the mesenteric arteries and disappeared in the sural and saphenous arteries. Although no difference in eNOS mRNA expression was found, the content of arginase-2 mRNA was significantly lower in young rats compared to adults. Serum levels of NO metabolites were two-fold higher in 2 wk-old rats than in adult rats. Along with that, arterial blood pressure was by half lower but rose more prominently after administration of l-NAME in young rats than in adults.. In young rats, tonic release of NO by the endothelium considerably weakens contractile responses of arteries supplying intestine, skin and skeletal muscles, which receive a high proportion of the cardiac output. Such anticontractile effect of NO can be an important mechanism responsible for the blood pressure reduction in immature circulatory system.

Topics: Age Factors; Animals; Arginase; Arterial Pressure; Arteries; Endothelium, Vascular; Hydrazines; Male; Muscle Contraction; Muscle, Smooth, Vascular; NG-Nitroarginine Methyl Ester; Nitrates; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitrites; Nitroarginine; Rats, Wistar; RNA, Messenger

Endothelium-dependent vasorelaxation in large vessels is mainly attributed to Nomega-nitro-L-arginine methyl ester (L-NAME)-sensitive endothelial nitric oxide (NO) synthase (eNOS)-derived NO production. Endothelium-derived hyperpolarizing factor (EDHF) is the component of endothelium-dependent relaxations that resists full blockade of NO synthases (NOS) and cyclooxygenases. H2O2 has been proposed as an EDHF in resistance vessels. In this work we propose that in mice aorta neuronal (n)NOS-derived H2O2 accounts for a large proportion of endothelium-dependent ACh-induced relaxation. In mice aorta rings, ACh-induced relaxation was inhibited by L-NAME and Nomega-nitro-L-arginine (L-NNA), two nonselective inhibitors of NOS, and attenuated by selective inhibition of nNOS with L-ArgNO2-L-Dbu-NH2 2TFA (L-ArgNO2-L-Dbu) and 1-(2-trifluoromethylphehyl)imidazole (TRIM). The relaxation induced by ACh was associated with enhanced H2O2 production in endothelial cells that was prevented by the addition of L-NAME, L-NNA, L-ArgNO2-L-Dbu, TRIM, and removal of the endothelium. The addition of catalase, an enzyme that degrades H2O2, reduced ACh-dependent relaxation and abolished ACh-induced H2O2 production. RT-PCR experiments showed the presence of mRNA for eNOS and nNOS but not inducible NOS in mice aorta. The constitutive expression of nNOS was confirmed by Western blot analysis in endothelium-containing vessels but not in endothelium-denuded vessels. Immunohistochemistry data confirmed the localization of nNOS in the vascular endothelium. Antisense knockdown of nNOS decreased both ACh-dependent relaxation and ACh-induced H2O2 production. Antisense knockdown of eNOS decreased ACh-induced relaxation but not H2O2 production. Residual relaxation in eNOS knockdown mouse aorta was further inhibited by the selective inhibition of nNOS with L-ArgNO2-L-Dbu. In conclusion, these results show that nNOS is constitutively expressed in the endothelium of mouse aorta and that nNOS-derived H2O2 is a major endothelium-dependent relaxing factor. Hence, in the mouse aorta, the effects of nonselective NOS inhibitors cannot be solely ascribed to NO release and action without considering the coparticipation of H2O2 in mediating vasodilatation.

Topics: Acetylcholine; Animals; Aorta, Thoracic; Biological Factors; Catalase; Dose-Response Relationship, Drug; Endothelium-Dependent Relaxing Factors; Endothelium, Vascular; Enzyme Inhibitors; Hydrazines; Hydrogen Peroxide; Imidazoles; In Vitro Techniques; Male; Mice; Mice, Inbred C57BL; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase Type I; Nitric Oxide Synthase Type III; Nitroarginine; Nitroprusside; Oligonucleotides, Antisense; RNA, Messenger; Vasodilation; Vasodilator Agents

To elucidate conflicting findings about the role of L-arginine/nitric oxide (NO) pathway in the locus coeruleus (LC), we investigated the effects of different drugs affecting NO concentrations by single-unit extracellular recordings from LC neurons in vivo and in vitro. In anesthetized rats, central (3.8-15.3 nmol i.c.v.) and local (16.5-66 pmol into the LC) administrations of the NO donor sodium nitroprusside, but not those of the inactive analogue potassium ferricyanide (16.5-66 pmol into the LC), increased by 65-84% the firing rate of LC neurons. In brain slices, low concentrations (50-200 microM) of diethylamine/NO complex, a short-lived NO releaser, also increased the neuron firing rate, although higher drug concentrations (400-800 microM) caused slowly reversible reductions of the firing activity. On the other hand, the NO synthase inhibitors N(omega)-nitro-L-arginine methyl ester (L-NAME) (148-371 nmol i.c.v.) and N(omega)-nitro-L-arginine (L-NA) (46 nmol i.c.v.) gradually decreased the firing rate of LC neurons, whereas the NO synthase substrate L-arginine (0.71-1.42 micromol i.c.v. and 0.6-4.8 nmol into the LC) increased the neuron activity. The latter effect was not mimicked by the vehicle or the less active isomer D-arginine (0.6-4.8 nmol into the LC). Unexpectedly, pretreatment with high concentrations of L-NAME (371 nmol and 18.5 micromol i.c.v.) or L-NA (45.6 nmol i.c.v. and 0.24 nmol into the LC) failed to block the effect of L-arginine. The glutamate receptor antagonist kynurenic acid (1 micromol i.c.v.) strongly reduced the effect of L-arginine but not that of sodium nitroprusside. These data confirm in vivo a direct excitatory effect of NO on LC neurons and suggest a tonic regulation of noradrenergic neurons by NO in vivo. L-arginine also excites LC neurons, but this effect may be caused by a nitric-oxide-unrelated glutamate-receptor-mediated mechanism.

Topics: Animals; Arginine; Hydrazines; Locus Coeruleus; Male; Neurons; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Norepinephrine; Rats; Rats, Sprague-Dawley

We investigated the role of nitric oxide (NO) in the modulation of respiratory-like activity recorded from hypoglossal rootlets in brainstem slices of neonatal rats (P0-P8). Sodium nitroprusside (SNP), S-Nitroso-N-acetyl-D,L-penicillamine (SNAP) and diethylamine-NO (DEA-NO), three NO-donors, reversibly increased hypoglossal burst amplitude with inconsistent effects on burst frequency. Similar effects were also obtained with the endogenous substrate of nitric oxide synthase (NOS), L-arginine, whereas the inactive enantiomer D-arginine had no effect. The NO-trap agent methylene blue significantly depressed both the amplitude and frequency of hypoglossal activity while hemoglobin depressed only the amplitude. Furthermore, the addition of NO-trap agents significantly attenuated the excitatory response to SNP. Inhibiting NOS with either N(omega)-Nitro-L-Arginine (L-NNA) or 7-Nitroindazole (7-NI), decreased the amplitude of hypoglossal activity with no effects on frequency. Histochemical analysis of NADPH-diaphorase activity, a marker for NOS, was performed on slices not treated pharmacologically and in brainstem sections of newborn rats, perfused in situ. Comparison between in vitro and in vivo conditions indicated that NOS activity was maintained in slice preparations. Neurons in the ambiguus and hypoglossal nuclei (dorsal division) exhibited a granular staining, suggesting the presence of NADPHd-positive terminals. Neurons with cytoplasmic staining were identified in regions connected to the hypoglossal nucleus (nucleus tractus solitarius, paramedian and gigantocellular reticular nuclei). These neurons might be involved in nitrergic control of hypoglossal activity. Both pharmacological and histochemical data suggest that endogenous NO may reinforce the output activity of the medullary respiratory network.

Topics: Action Potentials; Animals; Animals, Newborn; Brain Stem; Dose-Response Relationship, Drug; Enzyme Inhibitors; Histocytochemistry; Hydrazines; In Vitro Techniques; NADP; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Nitrogen Oxides; Nitroprusside; Penicillamine; Rats

The aim of the present study was to characterize the influence of the phosphatase type 1 and 2A inhibitor okadaic acid on non-adrenergic, non-cholinergic (NANC) neurotransmission in the rat gastric fundus. Okadaic acid (10-6 M), an inhibitor of protein phosphatases 1 and 2A, did not show any influence on the basal tonus or on a contraction plateau induced by 5-HT (10-7 M) within 30 min of observation. When okadaic acid (10-6 M) was applied 10 min prior to 5-HT (10-7 M), the contraction plateau of serotonin was unchanged. To investigate the inhibitory neurotransmission, the muscle strips were pre-contracted using 5-HT (10-7 M), and inhibitory stimuli were applied at the contraction plateau, which was stable over 30 min. The inhibitory effects of vasoactive intestinal peptide (VIP), nitric oxide (NO) and electrical field stimulation (EFS, 40 V, 0.5 ms, frequencies ranging from 0.5 to 16 Hz) were examined. When okadaic acid (10-6 M) was applied prior to EFS-induced NANC relaxation, significant attenuation of the inhibitory response was demonstrated (16 Hz: control: -92.4 +/- 1.9%; okadaic acid 10-7 M: -60.7 +/- 6.1%; okadaic acid 10-6 M: -25.3 +/- 3.4%; n=11; P < 0.01). By contrast, neither the concentration-dependent inhibitory actions of VIP (10-11-10-8 M) (VIP 10-8 M: -100%; VIP 10-8 M + okadaic acid 10-6 M: -89.9 +/- 8.3%; n=8; n.s) nor that of diethylamine nitric oxide (DEA-NO) (3 x 10-7-10-4 M) (DEA-NO 10-4 M: -95.3 +/- 8.4%; DEA-NO 10-4 M + okadaic acid 10-7 M: -98.3 +/- 6.3%; DEA-NO 10-4 M + okadaic acid 10-6 M: 96.5 +/- 7.6%; n=9; n.s.) on 5-HT induced contraction were altered by pre-incubation with okadaic acid (10-6 M). This is the first report that supports the concept that protein phosphatases 1 and 2A may contribute to the regulation of rat gastric fundus motility. The protein phosphatase inhibitor okadaic acid significantly reduces electrically induced inhibitory NANC responses, while leaving direct muscular effects of the inhibitory NANC neurotransmitters VIP and NO unaffected - suggesting a neural site of action. The potential roles of protein phosphatases on NANC neurotransmission remain to be clarified in detail, as this might offer a new pathway for modulating smooth-muscle function.

Topics: Animals; Carbazoles; Electric Stimulation; Enzyme Inhibitors; Gastric Fundus; Gastrointestinal Agents; Hydrazines; In Vitro Techniques; Indoles; Male; Muscle Relaxation; Muscle, Smooth; Nitric Oxide; Nitric Oxide Donors; Nitroarginine; Nitrogen Oxides; Okadaic Acid; Oxadiazoles; Phosphodiesterase Inhibitors; Phosphoprotein Phosphatases; Purinones; Pyrroles; Quinoxalines; Rats; Rats, Wistar; Synaptic Transmission; Vasoactive Intestinal Peptide

Experiments on isolated, perfused, working left ventricular (LV) hearts of 66 female Wistar rats were done to examine whether nitric oxide (NO) influences the effects of norepinephrine (NE) on coronary flow as well as on contraction and relaxation. Functional parameters were monitored before and after application of NE at a concentration of 3 X 10(-8) M in the absence and presence of the nitric oxide synthase (NOS) inhibitor L-nitro-arginine (L-NA) at a concentration of 1 X 10(-4) M and of the spontaneous NO donor sodium (Z)-1-(N,N-diethylamino) diazen-1-ium-1,2-diolat (DEA/NO) at a concentration of 1 X 10(-7) M. In control experiments, heart rate was varied by electrical stimulation between 200 and 400 beats/min. Within this range of heart rates, coronary flow and cardiac output remained constant, while stroke volume, LV peak pressure and LV dP/dt(max) decreased with increasing heart rate. NE increased coronary flow from 7.6 +/- 0.4 to 9.8 +/- 0.7 ml/min and induced the well-known positive chronotropic and inotropic effects. DEA/NO increased coronary flow; however, the inotropic and lusitropic parameters were not affected. Simultaneous infusion of NE with DEA/NO further increased coronary flow from 9.8 +/- 0.7 to 12.1 +/- 0.8 ml/min without a significant effect on any other functional parameter. When NOS was inhibited by L-NA, the positive inotropic effect of NE was attenuated. Cardiac output, however, was increased, while coronary flow did not change significantly. Under these conditions, NE increased dP/dt(max) by 65.5 +/- 5.8% (from 2999 +/- 97 to 4929 +/- 230 mmHg/s) compared with an increase by 92.8 +/- 6.7% (from 3770 +/- 82 to 7234 +/- 211 mmHg/s) under control conditions. Application of DEA/NO reversed the attenuated inotropic response, but relaxation remained partially impaired. Thus, the presence of NO seems to be necessary for the inotropic effect of NE to become manifest.

Topics: Animals; Cardiac Output; Coronary Circulation; Enzyme Inhibitors; Female; Heart; Heart Rate; Hydrazines; In Vitro Techniques; Myocardial Contraction; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Nitrogen Oxides; Norepinephrine; Perfusion; Rats; Rats, Wistar; Sympathomimetics

There is recent morphological evidence for an interaction of autonomic nerve fibers and extrinsic motor nerves of the rat esophagus. The aim of the present study was to investigate a possible functional role of this autonomic innervation of vagal motor fibers on rat esophageal smooth and striated muscle function in vitro. The entire esophagus with both Nn vagi, including the Nn recurrentes, was dissected and placed in an organ bath with oxygenated Krebs-Ringer buffer. Contractile activity was measured in longitudinal direction with a force transducer. Both Nn vagi were placed on a bipolar platinum electrode 2 cm apart from the esophagus. Vagal stimulation, applied for 1 s (40 V, 0.5 ms, 20 Hz) resulted in a biphasic contractile response, which was completely blocked by tetrodotoxin (10(-6) M). The first part consisted of a tetanic striated muscle contraction, which was abolished by tubocurarin (10(-5) M) but unaffected by atropine (10(-6) M) or hexamethonium (10(-4) M). In contrast, the second part was completely abolished by hexamethonium (10(-4) M) and atropine (10(-6) M), whereas tubocurarine (10(-5) M) showed no influence, suggesting a stimulation of preganglionic nerve fibers supplying esophageal smooth muscle (muscularis mucosae). In order to characterize possible autonomic transmitters of the ENS of the esophagus, the following experiments were carried out. The magnitude of the striated muscle response was unaffected by VIP (10(-7) M), 5-HT (10(-6) M) and galanin (10(-8) - 10(-7) M), whereas they caused an inhibition of the smooth muscle response (VIP: -53.8 +/- 4.2%; galanin 10(-8) M: - 18.5 +/- 2.2%; 10(-7) M: -40.4 +/- 2.9%; 5-HT: -78.2 +/- 2.1%). The inhibitory effects of VIP and galanin on smooth muscle were reversible by the antagonists VIP 10-28 and galanin 1-15. In the presence of the nitric oxide synthase (NOS) inhibitor L-NNA (10(-4) M), the smooth and striated muscle contraction were not significantly influenced. Exogenous application of the NO-donor DEA-NO (10(-4) M) reduced the smooth muscle contraction by -81.6 +/- 7.4%, but had no significant effect on the striated muscle contraction. Though immunohistochemical findings are highly suggestive of an nitrergic autonomic modulation of striated muscle contraction by enteric neurons, we could not demonstrate a NO-mediated action on striated muscle activity. Therefore, the physiological relevance of the immunohistochemical findings remain unclear.

Topics: Animals; Atropine; Enteric Nervous System; Enzyme Inhibitors; Esophagus; Galanin; Gastrointestinal Agents; Hexamethonium; Hydrazines; Male; Motor Neurons; Muscle Contraction; Muscle, Skeletal; Muscle, Smooth; Nicotinic Antagonists; Nitric Oxide Donors; Nitroarginine; Nitrogen Oxides; Oxadiazoles; Parasympatholytics; Quinoxalines; Rats; Rats, Wistar; Serotonin; Tetrodotoxin; Tubocurarine; Vagus Nerve; Vasoactive Intestinal Peptide

Nitric oxide (NO) is a putative participant in synaptic plasticity and demonstrations that exogenous NO can elicit the same plastic changes have been taken to support such a role. The experiments, carried out on the CA1 region of rat hippocampal slices, were aimed at testing this interpretation. A major component of tetanus-induced long-term potentiation (LTP) was lost in response to L-nitroarginine, which inhibits NO synthase, and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), which inhibits NO-sensitive soluble guanylyl cyclase (sGC). At 0.2 Hz afferent fibre stimulation, exogenous NO produced, concentration-dependently, a synaptic depression that reverted on washout to a persistent potentiation that occluded tetanus-induced LTP. The NO concentrations necessary (estimated in the 100-nM range), however, were mostly supramaximal for stimulating hippocampal slice sGC activity. Nevertheless the potentiation, but not the preceding depression, was blocked by ODQ. L-nitroarginine and an NMDA antagonist were similarly effective, indicating mediation by the endogenous NMDA receptor-NO synthase-sGC pathway. At a concentration normally too low to affect synaptic transmission but sufficient to stimulate sGC (estimated to be 50 nM), exogenous NO reversed the effect of L-nitroarginine and caused a potentiation which was blocked by ODQ. At a concentration inducing the depression/potentiation sequence, NO partially inhibited hippocampal slice oxygen consumption. It is concluded that, at physiological levels, exogenous NO can directly elicit a potentiation of synaptic transmission through sGC, provided that the synapses are suitably primed. At higher concentrations, NO inhibits mitochondrial respiration, which can result in an enduring synaptic potentiation due to secondary activation of the endogenous NO-cGMP pathway.

Topics: 2-Amino-5-phosphonovalerate; Adenosine Triphosphate; Animals; Cyanides; Cyclic GMP; Electric Stimulation; Enzyme Inhibitors; Excitatory Postsynaptic Potentials; Guanylate Cyclase; Hippocampus; Hydrazines; Long-Term Potentiation; Male; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Nitrogen Oxides; Oxadiazoles; Quinoxalines; Rats; Rats, Sprague-Dawley; Synaptic Transmission

1. In this investigation we studied the effects of nitric oxide on contractility and heart rate in normal saline-perfused rat hearts where shear stress-induced endothelial NO synthesis substantially contributes to total cardiac NO production. In addition, we sought to estimate the concentrations of exogenous NO producing inotropic effects. 2. We investigated the effects of glyceryl trinitrate (GTN), S-nitroso-d,l-penicillamine (SNAP), sodium (Z)-1-(N, N-diethylamino)diazen-1-ium-1,2-diolat (DEA/NO), and DEA/NO in the presence of the NO synthase inhibitor Nomega-nitro-L-arginine (L-NA) in constant-flow-perfused spontaneously beating rat Langendorff hearts and in rat working hearts. 3. In Langendorff hearts, GTN (10 nM to 100 microM, n = 32) induced a positive inotropic response that plateaued at 1 microM GTN with a maximal rate of increase of left ventricular pressure during ventricular contraction (+dP/dtmax) of 6. 33 +/- 2.56 % (n = 11, P < 0.5). Similarly, both spontaneous NO donors (0.1 nM to 1 microM, corresponding to approximately 0.03-0.3 microM NO) induced a positive inotropic response of 10.6 +/- 3.1 % (SNAP; n = 15, P < 0.05) and 11.5 +/- 2.7 % (DEA/NO, n = 15, P < 0. 05). 4. The positive inotropic effect of SNAP and DEA/NO progressively declined from 1 microM to 100 microM of the NO donors (corresponding to approximately 0.3-30 microM NO). 5. In the isolated working rat heart, 0.1 microM DEA/NO induced an increase of +dP/dtmax of 7.5 +/- 2.5 % (n = 9, P < 0.05). Inhibition of NO synthase by L-NA produced a 4-fold increase in this effect of DEA/NO. 6. We suggest that physiological NO concentrations support myocardial performance. In normal rat hearts the positive inotropic effect of NO appears to be almost maximally exploited by the endogenous NO production.

Topics: Animals; Cardiotonic Agents; Drug Synergism; Enzyme Inhibitors; Female; Heart; Hydrazines; In Vitro Techniques; Male; Myocardial Contraction; Myocardium; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Nitrogen Oxides; Nitroglycerin; Penicillamine; Rats; Rats, Wistar; S-Nitroso-N-Acetylpenicillamine; Vasodilator Agents

The 4-amino analogue of tetrahydrobiopterin (4-ABH(4)) is a potent pterin-site inhibitor of nitric oxide synthases (NOS). Although 4-ABH(4) does not exhibit selectivity between purified NOS isoforms, a pronounced selectivity of the drug towards inducible NOS (iNOS) is apparent in intact cells. This work was carried out to investigate the potential iNOS selectivity of 4-ABH(4) in isolated pig pulmonary and coronary arteries. Endothelium-dependent relaxations of pig pulmonary and coronary artery strips to bradykinin or calcium ionophore A23187 were inhibited by 4-ABH(4) in a concentration-dependent manner. Half-maximal inhibition was observed at 60 - 65 microM (pulmonary artery) and 200 - 250 microM 4-ABH(4) (coronary artery). Pig coronary artery strips precontracted with 0.1 microM 9, 11-dideoxy-9, 11-methanoepoxy-prosta-glandin F(2alpha) (U46619) showed a time-dependent relaxation (monitored for up to 18 h) upon incubation with 1 microg ml(-1) lipopolysaccharide (LPS). Addition of 10 microM 4-ABH(4) 1 h after LPS led to a pronounced inhibition of the LPS-triggered relaxation, whereas the pterin antagonist had no effect when given> or =4 h after LPS. Incubation of pulmonary and coronary artery strips with 1 microg ml(-1) LPS attenuated contractile responses to norepinephrine (1 microM) and U46619 (0.1 microM). This hyporeactivity of the blood vessels to vasoconstrictor agents was inhibited by 4-ABH(4) in a concentration-dependent manner [IC(50)=17.5+/-5.9 microM (pulmonary artery) and 20.7+/-3 microM (coronary artery)]. The effect of 0.1 mM 4-ABH(4) was antagonized by coincubation with 0.1 mM sepiapterin, which is known to supply intracellular BH(4) via a salvage pathway. These results demonstrate that 4-ABH(4) is a fairly selective inhibitor of iNOS in an in vitro model of endotoxaemia, suggesting that this drug and/or related pterin-site NOS inhibitors may be useful to increase blood pressure in severe infections associated with a loss of vascular responsiveness to constrictor agents caused by endotoxin-triggered iNOS induction in the vasculature.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Biopterins; Bradykinin; Calcimycin; Coronary Vessels; Dose-Response Relationship, Drug; Endothelium, Vascular; Endotoxins; Enzyme Inhibitors; Hydrazines; In Vitro Techniques; Lipopolysaccharides; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitroarginine; Nitrogen Oxides; Norepinephrine; Pteridines; Pterins; Pulmonary Artery; Swine; Vasoconstriction; Vasoconstrictor Agents; Vasodilation

1. We iontophoretically applied NG-nitro-L-arginine (L-NOArg), an inhibitor of nitric oxide synthase (NOS), to cells (n = 77) in area 17 of anaesthetized and paralysed cats while recording single-unit activity extracellularly. In twenty-nine out of seventy-seven cells (38%), compounds altering NO levels affected visual responses. 2. In twenty-five out of twenty-nine cells, L-NOArg non-selectively reduced visually elicited responses and spontaneous activity. These effects were reversed by co-application of L-arginine (L-Arg), which was without effect when applied alone. Application of the NO donor diethylamine-nitric oxide (DEA-NO) produced excitation in three out of eleven cells, all three cells showing suppression by L-NOArg. In ten cells the effect of the soluble analogue of cGMP, 8-bromo-cGMP, was tested. In three of those in which L-NOArg application reduced firing, 8-bromo-cGMP had an excitatory effect. In six out of fifteen cells tested, L-NOArg non-selectively reduced responses to NMDA and alpha-amino-3-hydroxy-5-methylisoxasole-4-propionic acid (AMPA). Again, co-application of L-Arg reversed this effect, without enhancing activity beyond control values. 3. In a further subpopulation of ten cells, L-NOArg decreased responses to ACh in five. 4. In four out of twenty-nine cells L-NOArg produced the opposite effect and increased visual responses. This was reversed by co-application of L-Arg. Some cells were also affected by 8-bromo-cGMP and DEA-NO in ways opposite to those described above. It is possible that the variety of effects seen here could also reflect trans-synaptic activation, or changes in local circuit activity. However, the most parsimonious explanation for our data is that NO differentially affects the activity of two populations of cortical cells, in the main causing a non-specific excitation.

Topics: Acetylcholine; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Arginine; Cats; Cyclic GMP; Electrophysiology; Enzyme Inhibitors; Excitatory Amino Acids; Hydrazines; Iontophoresis; N-Methylaspartate; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitrogen Oxides; Visual Cortex

Our objective was to test the hypothesis that local production of the vasorelaxant nitric oxide could regulate mammary blood flow. In four lactating Saanen goats, the response of mammary blood flow to intraarterial infusion of the nitric oxide donor diethylamine NONOate and the inhibitor of nitric oxide synthesis N omega-nitro-arginine was measured. Diethylamine NONOate induced a rapid and sustained increase of mammary blood flow in the infused gland only, suggesting a direct effect on vasculature of the mammary gland. In contrast, infusion of N omega-nitro-arginine decreased mammary blood flow by up to 35%, and the coinfusion of arginine, the nitric oxide precursor, with N omega-nitro-arginine markedly reduced its ability to decrease mammary blood flow. The distribution of nitric oxide synthase was investigated in cryosections of caprine and bovine mammary tissue by histochemical staining for NADPH-diaphorase activity and by immunocytochemistry using specific antibodies against two nitric oxide synthase isoforms. Both techniques revealed nitric oxide synthase in the vascular endothelium and secretory epithelium of the two species. Only antibodies against nitric oxide synthase-III showed specific staining. These results suggest that the mammary gland produces and responds to nitric oxide and, further, raise the possibility that the epithelium may control its own blood supply by secreting nitric oxide.

Topics: Animals; Blood Flow Velocity; Enzyme Inhibitors; Female; Goats; Hydrazines; Immunoenzyme Techniques; Lactation; Mammary Glands, Animal; NADPH Dehydrogenase; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitrogen Oxides