The inhibitory modulation of guinea-pig intestinal peristalsis caused by capsaicin involves calcitonin gene-related peptide and nitric oxide

The effect of capsaicin-induced stimulation of afferent neurons on peristalsis and the possible neural mediators involved in this action were examined in the guinea-pig isolated ileum. The intraluminal pressure threshold for eliciting peristaltic waves was used to quantify facilitation (decrease in threshold) or inhibition (increase in threshold) of peristalsis. Capsaicin (0.1-1 microM) caused an initial short-lasting stimulation of peristalsis followed by a prolonged inhibition of peristaltic activity. Capsaicin (1 microM) was ineffective when the gut segments had been pretreated with 3.3 microM capsaicin, which is indicative of an afferent neuron-dependent action of the drug. In contrast, the abolition of peristalsis caused by a high concentration of capsaicin (33 microM) was fully reversible on removal and reproducible on readministration of capsaicin, a feature characteristic of a nonspecific depression of smooth muscle excitability. Baseline peristalsis and the excitatory/inhibitory effect of capsaicin (1 microM) on peristalsis remained unaltered by a combination of the tachykinin NK1 receptor antagonist (+)-(2S, 3S)-3-(2-methoxybenzylamino)-2-phenyl piperidine (CP-99,994; 0.3 microM) and the tachykinin NK2 receptor antagonist (L(-)-N-methyl-N[4-acetylamino-4-phenyl-piperidine-2-(3,4- -dichlorophenyl)butyl]-benzamide (SR-48,968; 0.1 microM). Further experiments, performed in the presence of a low concentration of atropine (10 nM) showed that the calcitonin gene-related peptide (CGRP) antagonist human alpha-calcitonin gene-related peptide (8-37) [hCGRP(8-37); 10 microM] attenuated the delayed inhibitory effect of capsaicin on peristalsis, but did not influence baseline peristaltic activity and the capsaicin-induced facilitation of peristalsis. Blockade of nitric oxide (NO) synthesis by NG-nitro-L-arginine methylester (L-NAME, 300 microM) facilitated baseline peristaltic activity and reduced the delayed inhibition of peristalsis caused by capsaicin (1 microM) without affecting the initial peristalsis-stimulating action of capsaicin. The effects of L-NAME were prevented by L-arginine (1 mM). The data of the current study indicate that capsaicin-sensitive afferent neurons do not participate in the neural pathways subserving peristalsis in the guinea-pig small intestine, but modulate peristaltic activity upon stimulation with capsaicin. The initial stimulant action of capsaicin on peristalsis is independent of tachykinins acting via NK1 or NK2 receptors, while the delayed capsaicin-induced depression of peristalsis involves CGRP and NO.

Role of nitric oxide in impaired coronary circulation and improvement by angiotensin II receptor antagonist in spontaneously hypertensive rats

1. To determine whether coronary flow regulation by nitric oxide (NO) is impaired in the hypertensive heart (HTH), coronary perfusion was measured in isolated rat hearts using NO synthesis inhibitor L-NG-monomethyl arginine (L-NMMA) in Wistar-Kyoto (WKY) rat and spontaneously hypertensive rat (SHR) with and without chronic Nomega-nitro-L-arginine-methylester (L-NAME) treatment. Moreover, the effect of angiotensin II receptor antagonist (AT1 receptor antagonist) (TCV-116) on the impaired coronary circulation in HTH was examined. 2. Coronary flow (CF) was decreased in HTH accompanied with cardiac hypertrophy. The decreased response of CF to L-NMMA infusion was diminished in HTH. It is suggested that NO production was reduced in coronary vasculature in HTH. 3. In chronic L-NAME treated SHR, blood pressure and cardiac hypertrophy were accelerated. Although coronary flow resistance (CFR) was increased, the increased response of CFR to L-NMMA infusion was not altered. 4. The AT1 antagonist improved total minimal coronary flow resistance (MCFR) restoring CFR response in SHR, although it did not recover CFR response in chronic L-NAME treated SHR. 5. Taken together the findings suggest that NO production was exhausted in the coronary artery even in the developing stage of hypertension and this exhaustion could contribute to the impairment of coronary circulation of HTH.

Is nitric oxide involved in 5-HT-induced fluid secretion in the gut?

The present study was undertaken to test the hypothesis that 5-HT stimulates nitric oxide (NO) generating neurons, and that these neurons participate in the mediation of 5-HT-induced fluid secretion. 5-HT induced electrogenic Cl- secretion in guinea-pig distal colon. This response was abolished by tetrodotoxin but not by atropine. The maximum response to 5-HT (10(-5) M) was inhibited by approximately 65% (P < 0.05, n = 6) by the NO synthase inhibitor, NG-nitro-L-arginine (L-NNA, 10(-4) M). The substrate of NO synthase, L-Arg (10(-3) M) reversed the inhibition of 5-HT-induced secretions by L-NNA. 5-HT-induced diarrhea in fasted mice was reduced by atropine in vivo. NG-Nitro-L-Arg methyl ester (L-NAME, 1-32 mg/kg, i.p.) dose-dependently inhibited 5-HT (1 mg/kg)-induced diarrhea. The inhibitory effect of L-NAME was reversed by L-Arg, but not D-Arg (600 mg/kg, i.p., respectively). Taken together, these data suggest that 5-HT-induced fluid secretion in the gut is partly due to the activation of neurons that generate NO.

Adenosine and the endothelium-dependent modulation of 3H-noradrenaline release in the canine pulmonary artery

This study aimed at characterizing the influence of endothelium on noradrenaline release from the canine pulmonary artery. Tritium overflow from intact or endothelium-free vessels preloaded with 0.2 mumol.l-1 3H-noradrenaline was evoked by electrical stimulation (1 Hz, during 5 min) or potassium (25-100 mmol.l-1). The fractional release of tritium evoked by electrical stimulation was increased by removing the endothelium [from 1.7 (1.2; 2.4) to 2.7(2.3; 3.2) x 10(-5).pulse-1, n = 10; P < 0.05]. Neither NG-nitro-L-arginine methyl ester (L-NAME) (up to 300 mumol.l-1) nor indomethacin (up to 30 mumol.l-1), nor endothelin-1 (up to 30 nmol.l-1), nor suramin (up to 300 mumol.l-1) changed tritium release evoked by electrical stimulation. In contrast, the selective A1-adenosine antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (3.3-33 nmol.l-1) concentration-dependently increased, and the selective A1-adenosine agonist N6-cyclopentyladenosine (CPA) (3.3-100 nmol.l-1) concentration-dependently decreased the evoked release of noradrenaline. Since the effects of DPCPX were observed in endothelium-intact tissues only, it may be concluded that adenosine secreted by the endothelium activates prejunctional release-inhibiting A1-receptors. Tetraethylammonium (TEA) (3.3-33 mmol.l-1) enhanced tritium overflow evoked by electrical stimulation more in endothelium-free than in endothelium-intact vessels, indicating that some K(+)-channel opener is involved in the inhibitory role of endothelium on noradrenaline release. Since it had been previously shown that A1-adenosine receptors are coupled to K(+)-channels, it is suggested that adenosine may inhibit noradrenaline release through the opening of K(+)-channels. In conclusion, the results show that in the canine pulmonary artery, adenosine is a good candidate for the endothelium-dependent inhibitory factor which is responsible for the reduction of noradrenaline release evoked by electrical stimulation.

The role of nitric oxide in the control of protein secretion in the submandibular gland of the cat

Submandibular salivary responses to stimulation of the parasympathetic chorda lingual innervation have been investigated in anaesthetized cats in the presence and absence of N omega-arginine-L-methyl ester (L-NAME) to block the synthesis of nitric oxide. Stimulation either at 2 Hz continuously or at 20 Hz for 1 s at 10 s intervals produced an abrupt fall in submandibular vascular resistance and initiated a flow of submandibular saliva. Neither of these responses differed significantly from the other but the output of protein was significantly potentiated (P < 0.05) when the high-frequency intermittent pattern of stimulation was employed. This potentiation of protein output was abolished in the presence of L-NAME, when the output of protein from the gland was closely similar, whichever pattern of stimulation was employed. Additional administration of atropine completely blocked all submandibular responses to parasympathetic stimulation showing that, in the presence of L-NAME, each response was due to release of acetylcholine acting on muscarinic receptors. The intermittent pattern of chorda lingual nerve stimulation produced a significant rise in the output of vasoactive intestinal peptide (VIP) from the gland (P < 0.01) and this response was significantly reduced following administration of L-NAME (P < 0.05). The results are consistent with the contention that stimulation of the parasympathetic innervation in bursts, which increases the amount of VIP released from the postganglionic nerve terminals, enhances the output of protein in submandibular saliva in the cat. The mechanism involves nitric oxide (NO), which may act, at least in part, presynaptically by modulating VIP release.

Expression of inducible nitric oxide synthase in smooth muscle cells from rat penile corpora cavernosa

Nitric oxide (NO), the main mediator of penile erection, is assumed to be synthesized in the penis by the neuronal constitutive nitric oxide synthase (nNOS). However, nNOS has not been identified in the penile smooth muscle, the target of NO action. The other NOS isozymes, the inducible NOS (iNOS) and the endothelial NOS (eNOS) have not been reported in any penile tissue. The smooth muscle vascular and trabecular tissue from rat corpora cavernosa is represented in vitro by cell cultures designated RPSMC. To determine whether iNOS can be expressed in penile smooth muscle, RPSMC were treated with different lymphokines and/or bacterial lipopolysaccharide (LPS). The selected inducer, LPS/interferon, elicited at 48 hours up to a 50-fold increase in nitrites in the medium; the nitroarginine methyl ester (L-NAME), aminoguanidine, actinomycin D, cycloheximide, transforming growth factor-beta1 (TGF-beta1), and dexamethasone, but was resistant to nifedipine and platelet-derived growth factor AB (PDGF-AB). iNOS induction increased with cell passage. The [3H]L-arginine/citrulline measurement of NO synthesis with intact cells confirmed these results. Incubations of soluble and particulate fractions showed that the cytosol contained most of the activity (Km = 43 microM), which was partially inhibited by ethyleneglycal-bis-tetraacetic acid (EGTA). The 4.4-kb iNOS mRNA peaked at a late period (24-30 hours) and remained high for up to 72 hours. iNOS mRNA induction was strongly inhibited by actinomycin D and dexamethasone, partially inhibited by TGF-beta1, inhibited slightly by PDGF-AB, and unaffected by nifedipine. These results show that iNOS can be expressed in RPSMC in a cell passage-dependent fashion that has so far not been reported for other cell lines, and that the induction reaches much higher levels than in rat or human vascular smooth muscle cells. The expression pattern is also distinctive for the penile cells in time course of induction, Ca2+ dependence, response to certain agents, and mRNA stability.

Biphasic L-arginine uptake by the isolated guinea-pig heart

L-Arginine is the physiological substrate for the formation of nitric oxide (NO) and accounts for the biological activity of endothelium-derived relaxing factor. We have studied L-arginine transport in the heart using a rapid dual-isotope dilution technique. The time course of L-[3H]arginine uptake (extraction) by the isolated perfused guinea-pig heart was found to occur in two phases. The first phase reached a plateau in 6.6 +/- 0.6 s and lasted 8.8 +/- 0.7 s, whereas the second phase developed a plateau after 16.3 +/- 0.8 s. The first phase of maximal uptake (Umax,1) accounted for 13.4 +/- 1.4% of the total uptake and the second (Umax,2) for 32.3 +/- 1.8%. The two phases of uptake were inhibited by unlabelled L-arginine in a dose-dependent manner, which suggests that both phases are carrier mediated. The degree of inhibition of Umax,1 and Umax,2 by unlabelled L-arginine was not significantly different. Studies of the kinetics of uptake of these processes revealed an apparent Km,1 of 183 +/- 10 microM with a Vmax,1 of 50 +/- 10 nmol min-1 g-1 for the first phase and Km,2 of 167 +/- 14 microM with a Vmax,2 of 93 +/- 13 nmol min-1 g-1 for the second phase of uptake. These results suggest a similar affinity for the receptors of both transport systems, but with different values for Vmax (P < 0.05). In contrast, 1 mM unlabelled D-arginine had no effect on either the first or second phase of uptake of L-[3H]arginine by the heart, which suggests that these processes are stereospecific. In the presence of the L-stereoisomer of nitro-arginine-mono-methyl ester (L-NAME), a potent inhibitor of NO synthesis, the Umax,1 was inhibited by about 60% while Umax,2 was inhibited by only 20%, which suggests that there is a difference in the effect of L-NAME on the two phases of L-arginine uptake. The first phase most probably represents uptake into the capillary wall, i.e. endothelium and smooth muscle, while the second phase represents entry into the extra-endothelial compartment, i.e. the cardiac myocytes and fibroblasts.

Nitric oxide synthase inhibition does not impair visual or spatial discrimination learning

Nitric oxide (NO) is a candidate retrograde messenger involved in synaptic plasticity, and is linked to the cholinergic system in the brain. We examined the role of NO in the acquisition of visual and spatial discriminations by daily administration of either saline or 1-nitroarginine methyl ester (L-NAME), an NO synthase inhibitor. Brains were assayed for NO synthase activity and two presynaptic cholinergic markers: hemicholinium-3 (HC-3) binding, which determines the number of sodium-dependent high-affinity choline uptake sites, and activity of choline acetyltransferase (ChAT), which is the synthetic enzyme for acetylcholine. In both behavioral tasks, the acquisition rate was not different between groups. L-NAME reduced NO synthase activity by 85% in all brain areas assayed and HC-3 binding by 38% in hippocampus and 48% in posterior cortex. ChAT activity was not different between groups in any region assayed. These data suggest that NO does not play a role in visual or spatial discrimination learning. However, NO synthase inhibition may play a role in the regulation of cholinergic activity.

Comparison of the nitric oxide synthase inhibitors methylarginine and aminoguanidine as prophylactic and therapeutic agents in rat adjuvant arthritis

OBJECTIVE

To compare the nitric oxide synthase (NOS) inhibitors NG-methyl-L-arginine (L-NMA) and aminoguanidine (AG) as prophylactic and therapeutic agents in rat adjuvant induced arthritis (AIA).

METHODS

Arthritis was induced in male Lewis rats by the injection of adjuvant into the base of the tail. L-NMA or AG was administered twice daily by gastric intubation starting at the time of adjuvant injection, just before the onset of clinical symptoms, or after the onset of clinical symptoms. Paw swelling, plasma fibrinogen levels and urinary NO2-/NO3- excretion were measured to assess the effect of the inhibitors on the arthritis response and whole body NO biosynthesis. Selected joints were also evaluated histopathologically. The abilities of L-NMA, AG and another NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), to inhibit NO production by chondrocytes and synoviocytes were also compared.

RESULTS

Treatment with L-NMA (400 mg/kg/day) or AG (500 mg/kg/day) reduced the urinary excretion of NO2-/NO3- to the control level. L-NMA suppressed the development of AIA when administered prophylactically; however, its antiarthritic properties declined with increasing delay of application. It was only weakly effective against established AIA. AG had neither a prophylactic nor a therapeutic antiarthritic effect. AG and L-NAME were much weaker inhibitors of NO production by chondrocytes and synoviocytes than L-NMA.

CONCLUSION

Although L-NMA completely suppresses the development of AIA when administered prophylactically, it is much less effective when administered therapeutically. Furthermore, not all inhibitors of NOS show equal prophylactic activity against AIA. In addition, NOS inhibitors may be only weakly therapeutic, or even detrimental, in established disease. These findings should be considered when evaluating NOS inhibitors as potential therapeutic agents for the treatment of established human arthritis.

A role for nitric oxide in X-ray contrast material toxicity

RATIONALE AND OBJECTIVES

We assessed the role that nitric oxide (NO) plays in contrast media (CM) toxicity, using 100% lethal dose (LD100) studies in hyperimmune Brown Norway (BN) rats.

METHODS

Ninety-two BN rats and 41 Sprague-Dawley (SD) rats underwent CM LD100 tail vein injections with methylglucamine iothalamate or sodium iothalamate to the point of cessation of respiration. Methylglucamine hydrochloride also was injected. The injections were accompanied by L-arginine (L-Arg) or D-arginine (D-Arg) analogues or by an H1 blocker. L-Arg analogues inhibit NO formation, and D-Arg analogues do not.

RESULTS

An L-Arg analogue, but not a D-Arg analogue, increased the tolerance of BN rats (p < .005) for methylglucamine iothalamate but not for sodium iothalamate. The L-Arg analogue also protected BN rats against methylglucamine chloride injections (p < .002). H1 blockade protected BN rats against methylglucamine iothalamate (p < .0005) and methylglucamine chloride (p < .005) injections. None of these measures altered the CM tolerance of SD rats. In SD rats, injections of either methylglucamine iothalamate or sodium iothalamate along with a D-Arg analogue or normal saline were better tolerated than similar injections in BN rats (p < .01 and .002 for methylglucamine iothalamate and sodium iothalamate, respectively). In SD rats but not BN rats, sodium iothalamate was better tolerated than was methylglucamine iothalamate (p < .0005).

CONCLUSION

NO appears to play a significant role in BN rats LD100 CM toxicity and has been implicated by others in the blood pressure fall characterizing some forms of antigen-induced anaphylaxis [1, 2]. The results of the current study and the literature suggest that methylglucamine-modulated release of histamine from mast cells may underlie the NO production.

Functional role of nitric oxide in guinea pig tracheal epithelium

Nitric oxide (NO) may play an important regulatory role in airway function. We have, thus, investigated in vitro whether epithelium derived NO may modulate cholinergic neurotransmission, via release of NO in guinea pig trachea, by using L-arginine (L-ARG), a precursor of NO synthesis, and L-N(G)-nitro-arginine-methyl-ester (L-NAME), an inhibitor of NO synthase. Results show that L-ARG and L-NAME modify acetylcholine sensitivity in epithelium-intact smooth muscle preparations, suggesting a probable NO synthesis by tracheal guinea pig epithelium.

The effects of physostigmine, L-arginine and NG-nitro-L-arginine methyl ester (L-NAME) on the mean arterial pressure of the rat

The effects of physostigmine, L-arginine and NG-nitro-L-arginine methyl ester (L-NAME) were investigated in urethane-anaesthetized rats. The drugs were chosen because physostigmine has been known to produce an increase in peripheral adrenergic activity, whereas L-arginine and L-NAME have been known to modulate nitric oxide (NO) production. Slow infusion of L-arginine produced significant hypotension, but only in animals pretreated by physostigmine. L-NAME applied in the same way produced a slow developing increase in blood pressure, but not in animals pretreated by physostigmine. The pressor responses to physostigmine were potentiated if the drug was injected during infusion of L-NAME, and depressed if the drug was injected after stopping L-NAME infusion (in rats not pretreated with physostigmine). It is concluded that L-arginine-NO pathways act in vivo to oppose peripheral vasoconstrictor influences coupled with central cholinergically mediated activation of the adrenergic system, as produced by physostigmine. In this way, NO is part of a general mechanism for blood pressure regulation.

Extremely-low-frequency magnetic fields disrupt rhythmic slow activity in rat hippocampal slices

Several studies have indicated that weak, extremely-low-frequency (ELF; 1-100 Hz) magnetic fields affect brain electrical activity and memory processes in man and laboratory animals. Our studies sought to determine whether ELF magnetic fields could couple directly with brain tissue and affect neuronal activity in vitro. We used rat hippocampal slices to study field effects on a specific brain activity known as rhythmic slow activity (RSA), or theta rhythm, which occurs in 7-15 s bursts in the hippocampus during memory functions. RSA, which, in vivo, is a cholinergic activity, is induced in hippocampal slices by perfusion of the tissue with carbachol, a stable analog of acetylcholine. We previously demonstrated that the free radical nitric oxide (NO), synthesized in carbachol-treated hippocampal slices, lengthened and destabilized the intervals between successive RSA episodes. Here, we investigate the possibility that sinusoidal ELF magnetic fields could trigger the NO-dependent perturbation of the rate of occurrence of the RSA episodes. Carbachol-treated slices were exposed for 10 min epochs to 1 or 60 Hz magnetic fields with field intensities of 5.6, 56, or 560 microT (rms), or they were sham exposed. All exposures took place in the presence of an ambient DC field of 45 microT, with an angle of -66 degrees from the horizontal plane. Sinusoidal 1 Hz fields at 56 and 560 microT, but not at 5.6 microT, triggered the irreversible destabilization of RSA intervals. Fields at 60 Hz resulted in similar, but not statistically significant, trends. Fields had no effects on RSA when NO synthesis was pharmacologically inhibited. However, field effects could take place when extracellular NO, diffusing from its cell of origin to the extracellular space,was chelated by hemoglobin. These results suggest that ELF magnetic fields exert a strong influence on NO systems in the brain; therefore, they could modulate the functional state of a variety of neuronal ensembles.