Selective potentiations in opioid analgesia following scopolamine pretreatment

The effects of the muscarinic receptor antagonist scopolamine upon analgesia induced by d-ala-d-leu-enkephalin (DADL), beta-endorphin (BEND) and morphine were examined. While scopolamine (10 mg/kg, IP) significantly potentiated the analgesic responses following DADL (40 g, ICV) and morphine (5 mg/kg, SC) on the jump test, it failed to alter significantly BEND (1 g, ICV) analgesia.     

Bombesin-induced contractions of guinea pig lung strips are modulated by endogenous nitric oxide

We have investigated the effects of a nitric oxide (NO) biosynthesis inhibitor N^\sw-nitro-L-arginine methyl ester (l-NAME) on the bombesin-evoked contraction of guinea pig parenchymal lung strips. The bombesin-induced contractions of lung strips were significantly increased after l-NAME (300 M) pre-treatment. The maximal response was increased (P < 0.01) by 37% after l-NAME treatment when compared with the control group. The pD₂ value was not influenced by l-NAME pre-treatment. The enhancement of the bombesin-induced contraction caused by l-NAME was reversed by addition of an excess of the NO precursor-l-arginine (600 M) but not by the addition of its inactive enantiomer d-arginine (600 M). Like l-NAME, methylene blue (1 M), an agent that inhibits the soluble guanylyl cyclase activated by NO, significantly increased (P < 0.01) the maximal contraction induced by bombesin (183 ± 16 mg) when compared with the control group (141 ± 15 mg). When tested against other agonist-induced contractions, l-NAME did not change the responsiveness of parenchymal lung strips to bradykinin or carbachol but significantly increased the lung contraction induced by histamine. NO synthesis inhibition resulted in a pronounced increase in the bombesin-induced contraction of guinea-pig lung strips. Our results suggest that bombesin contributes to NO synthesis and release which then acts to reduce the contraction of the lungstrip in response to bombesin.     

Effect of LP-805, a releaser of endothelium-derived nitric oxide,on systemic vasodilatation in vivo

Summary We have investigated relations between hypotensive responses to LP-805, a newly synthesized vasodilator, and the production of nitric oxide (NO), in anesthetized rats. LP-805 (0.1–0.5 mg/kg, i.v.) or acetylcholine (ACh) (0.3 – 3.0 g/kg, i.v.) caused a dose-dependent transient decrease in diastolic blood pressure. The decrease induced by 0.3 mg/kg LP-805 (i.v.) was partially inhibited by pretreatment with N^G-nitro-l-arginine (LNNA), a specific inhibitor of endothelial NO synthase, but the responses to lower or higher doses of LP-805 (0.1 or 0.5 mg/kg, i.v.) were not affected. The dose-dependent decrease in diastolic blood pressure, caused by LP-805, was not affected by pretreatment with l- or d-arginine. The dose-dependent decrease in diastolic blood pressure caused by ACh was not affected by pretreatment with L-NNA or with l- or d-arginine. The hypotensive response to 20-min infusions of LP-805 (100 g/kg per min) wassignificantly inhibited by pretreatment with L-NNA (10 mg/kg, i.v.). The half-recovery times (T_1/2) of LP-805 or ACh-induced depressor responses were shortened by pretreatment with L-NNA. They were prolonged by l-arginine, but not by d-arginine. This shortening, by L-NNA, of the half-recovery time after LP-805 or ACh was reversed by l-arginine, but not by d-arginine. The T_/2 of the LP-805-induced hypotensive response was not affected by pretreatment with indomethacin (1 mg/kg, i.v.). In the presence of L-NNA (10 mg/kg, i.v.), the T_/2 of the LP-805-induced hypotensive response was not affected by pretreatment with indomethacin. The results suggest that the LP-805-induced hypotensive response may be related to direct or indirect activation of NO synthase in vascular endothelial cells, and to release of endothelium-derived NO. Correspondence to M. Inazu at the above address     

Functional relation between nitric oxide and noradrenaline for the modulation of vascular tone in rat mesenteric vasculature

As previously reported, N-nitro-l-arginine (l-NNA), an inhibitor of nitric oxide (NO) synthesis, decreased transmural field stimulation (TFS)-induced noradrenaline overflow from the isolated perfused rat mesenteric vasculature attached to the intestine. The decrease was attenuated by l-arginine. This suggests that NO may increase noradrenaline release (Yamamoto et al. 1993).The present experiments with this preparation were done in order to monitor changes in vascular perfusion pressure caused by TFS or by noradrenaline infusion in parallel with those in the noradrenaline outflow caused by TFS in the presence of atropine (0.1 mol/l) (to block acetylcholine-induced release of endothelial NO) and of indomethacin (3 mol/l) (to inhibit l-NNA-induced production of vasoconstrictor prostanoids). (1) TFS (2–10 Hz) caused a frequency-dependent increase in noradrenaline overflow and perfusion pressure. (2) l-NNA (10 and 30 mol/l) caused a concentration-dependent inhibition of TFS-induced noradrenaline overflow, whereas the TFS-induced pressure increase was augmented by l-NNA in a concentration-dependent manner. At any given concentration of l-NNA, the potentiation of vasoconstriction by l-NNA became greater in magnitude as the frequency of the TFS was raised. (3) Infusion of noradrenaline (0.38–6 nmol) caused a dose-dependent increase in perfusion pressure up to a value comparable with that caused by TITS. The pressure increase in response to noradrenaline infusion was also enhanced by l-NNA, relatively, to a greater extent than the enhancement, by l-NNA, of the pressure response to TFS. (4) These effects of l-NNA were significantly attenuated by l-arginine (0.3 mmol/l) or sodium nitroprusside (1 mol/l). Our results suggest that NO, presumably originating from several sites, may stimulate the release of noradrenaline in the mesenteric vasculature and that the consequent rise in circulating noradrenaline, in turn, causes the liberation of endothelial NO. Correspondence to: R. Yamamoto at the above address     

The cytosol of N1E-115 neuroblastoma cells synthesizes an EDRF-like substance that relaxes rabbit aorta

Summary The cytosolic fraction of N1E-115 neuroblastoma cells catalysed the l-arginine- and NADPH-dependent formation of a substance that relaxed endothelium-denuded strips of rabbit aorta. Relaxations in response to this substance were enhanced in the presence of superoxide dismutase. N-Nitro-l-arginine and N^G-monomethyl-l-arginine, two inhibitors of EDRF synthesis, markedly attenuated the relaxations. Hemoglobin, a scavenger of EDRF, and methylene blue, an inhibitor of soluble guanylate cyclase, completely abolished the relaxation to N1E-115 cytosol. In contrast, the cyclo-oxygenase inhibitor indomethacin did not alter the relaxations. These data demonstrate that the cytosol of a neuronally-derived cell line is able to synthesize a substance with pharmacological properties similar to EDRF.This work was supported in part by Research Grants AM 30787 and HL 28474 from the National Institutes of Health, USA     

Low dose calcium-antagonism compensates for impaired myocardial blood supply resulting from deficient nitric oxide synthesis

Coronary artery disease (CAD) has been documented to be usually associated with endothelial dysfunction. Thus, the present experiments were performed to investigate whether non-hypotensive doses of calcium antagonists can compensate for the effects of deficient endogenous formation of nitric oxide (NO) in the coronary vascular bed in vivo. In chronically instrumented conscious dogs (n = 6) which were prepared for the measurement of coronary blood flow (CBF), coronary diameter of the left circumflex artery (LCX), mean arterial blood pressure (MAP) and heart rate (HR), continuous intravenous infusions of 0.2 g/kg/min nisoldipine (NI) or 2.0 g/kg/min diltiazem (DT) were performed after intracoronary pretreatment with either vehicle or the inhibitor of NO synthesis NG-nitro-l-arginine methyl ester (l-NAME, 6 mg/kg). NI dose-dependently increased CBF up to a maximum of +74±7.5% from control, while LCX diameter and HR were not significantly affected. MAP fell slightly (–5±3 mmHg). The maximum CBF increase in response to diltiazem at 10-fold higher doses was +39±13% while MAP fell –12±2 mmHg at the highest cumulative dose (100 g/kg). HR and LCX diameter remained unaltered. Pretreatment with l-NAME caused marked hypertension and bradycardia, associated with reduction in CBF (-34±16%) and LCX diameter (–9.5±0.8%). Subsequent infusion of NI or DT increased CBF up to the control values obtained before l-NAME. In contrast, both calcium antagonists failed to reverse the effects on MAP or HR. These results suggest that calcium antagonists at low doses restore normal myocardial perfusion during impaired synthesis of NO and may thus help to compensate for an impaired coronary dilator capacity in diseases which are associated with endothelial dysfunction.     

Developmental Responses of a Terrestrial Insect Detritivore, <Emphasis Type="BoldItalic">Megaselia scalaris</Emphasis> (Loew) to Four Selenium Species

Megaselia scalaris (Loew) (Diptera: Phoridae) is an important and ubiquitous terrestrial detritivore that consumes both animal and plant material. Because both plants and animals convert selenium pollutants into various forms, the relative toxicities of ecologically relevant concentrations of sodium selenate, sodium selenite, seleno-L-methionine, and Se-(methyl) selenocysteine hydrochloride to larvae were assessed in diet bioassays. In addition, ovipositional preferences of adults and developmental effects on the eggs and larvae were measured. With chronic exposure selenocysteine was the most toxic of the selenium species to the larvae (LC₅₀: 83 g/g wet weight), followed by seleno-L-methionine (LC₅₀: 130 g/g), selenate (LC₅₀: 258 g/g), and selenite (LC₅₀: 392 g/g). Ovipositing females did not discriminate between the highest treatment concentrations of any of the pollutants as compared to the controls, indicating a lack of avoidance behavior. Larval development time was significantly increased with exposure to selenate at 100 g/g wet weight and above, selenite at 300 g/g and above, and at 50 g/g and 25 g/g and above for seleno-L-methionine and selenocysteine respectively. Pupal development was not affected by any of the selenium treatments. Significant differences between male and female adult eclosion times were observed, with females eclosing later than males as selenium concentrations increased. Significant decreases in larval survival relative to controls occurred at the lowest treatment tested (100 g/g) for both selenate and selenite and at 100 g/g for seleno-L-methionine, and 50 g/g for selenocysteine. The population level implications of lack of avoidance of contaminated food, and the effects of increased development times, reduced survivorship, and non-synchronized male and female emergence are discussed.     

Morphine-like discriminative stimulus effects of opioid peptides: possible modulatory role ofd-Ala2-d-Leu5-enkephalin (DADL) and dynorphin A(1-13)

The role of the different opioid receptors was studied in rats trained to discriminate SC injections of 3.0 mg/kg morphine from saline by tests for generalization to graded doses of morphine and receptor-selective peptides administered into the lateral cerebral ventricle. Dose-dependent morphine-like stimulus effects were produced over a wide range of doses (0.001–30 g), depending upon ligand and animal, by morphine, by themu-selective peptides DAGO[d-Ala²-NMePhe⁴-Gly(ol)-enkephalin] and FK33824[d-Ala²,NMePhe⁴-Met(O)⁵-(ol)-enkephalin], and by thedelta-selective peptide, DADL[d-Ala²,d-Leu⁵enkephalin]. The order of relative potency of these substances was: FK33824>DAGO>morphine>DADL. In contrast, DPLPE[d-Pen²,l-Pen⁵)enkephalin], which has much greaterdelta receptor selectivity than does DADL, and dynorphin A(1-13) (0.1–10 g), akappa-receptor agonist, engendered choice responding appropriate for saline. When 1.0 g DADL, a dose lacking morphine-like discriminative effects, was administered concurrently with SC morphine, the stimulus effects of morphine were potentiated. Concurrent administration of 10 g dynorphin A(1-13) and morphine attenuated the stimulus effects of morphine inconsistently. These results support previous findings thatmu-opioid receptors are of primary importance in mediating the morphine-like discriminative effects of opioid peptides. They also suggest that morphine-like discriminative effects can be modulated by other types of opioid receptors.     

Lisuride,a potent drug in the treatment of muscular rigidity in rats

Summary Persistent and transient muscular rigidities were induced by 6-aminonicotinamide (6-AN) and reserpine, respectively, in rats and recorded electromyographically.Very low doses of lisuride (25 or 50 g/kg) reduced or abolished the increased electromyographic activity in the gastrocnemius muscle. Similar results were obtained with the combination of L-DOPA (100 mg/kg) plus benserazide (25 mg/kg). Methysergide was inactive. It is suggested that lisuride could be of value in the therapy of Parkinson's disease.N-(D-6-methyl-8-isoergolenyl)-N,N-diethylcarbamide hydrogen maleate     

Tryptophan antidepressant ‘physiological sedative’: Fact or fancy?

Some recent publications relating to the allegedly antidepressive and sedative effects of L-tryptophan the precursor of 5-HT have been reviewed.The evidence to date suggests that the amino acid is as effective as standard tricyclic drugs in alleviating the symptoms of depression, especially those cases presenting with mainly psychomotor retardation, and is synergistic with MAOIs. L-Tryptophan would also appear to be a physiological sedative. This action, however, appears to be related to the time of administration and at present has only been demonstrated at night, when endogenous levels of 5-HT are at their peak.In terms of practical therapeutics L-tryptophan would appear to have greater potential as an antidepressant than as a sedative.     

Opiate receptors in the rabbit iris

Summary Evidence pointing to the presence of opiate receptors in the rabbit iris was obtained in an in vivo study of the effects on the pupil of the intraocular injection of morphine (10–100 g) and d-Ala²-met-enkephalinamide (d-Ala-E) (5–50 g). Both opiates induced a significant dose-dependent decrease in pupillary size and an appreciable fluctuation of pupillary size. I.v. administration of naloxone (0.5 mg/kg) before or after injection of opiates prevented the miotic effect and the fluctuation of pupil size. The parallelism of the dose-response curves of opiates in the presence and absence of naloxone indicated competitive reversible antagonism.     

Evidence for the role of nitric oxide in nicotine-induced locomotor sensitization in mice

Rationale Nitric oxide (NO) is implicated in both acute effects of addictive drugs and development of dependence to them. We investigated the role of NO in nicotine-induced locomotor sensitization.Objectives The effects of N-nitro-l-arginine methyl ester (l-NAME), a NO synthase inhibitor, and a combination of a NO precursor l-arginine and l-NAME on nicotine-induced locomotor sensitization were investigated in Swiss Webster mice.Methods Sensitization to psychomotor stimulating effect of nicotine was rendered by seven injections of nicotine (1 mg/kg) on every other day. To investigate their effect on the development of sensitization to nicotine, l-NAME (15–60 mg/kg) and l-arginine (1 g/kg) were given before nicotine administration during the first seven sessions. To investigate the effect of these compounds on the expression of nicotine sensitization, after a 4-day drug-free period another group of mice received a challenge injection of nicotine on day 18.Results Nicotine (1 mg/kg) produced a robust locomotor sensitization in mice. The doses of 30 mg/kg and 60 mg/kg of l-NAME blocked the development of sensitization to nicotine; and, l-arginine (1 g/kg) pretreatment reversed this effect of l-NAME. Likewise, the doses of 30 mg/kg and 60 mg/kg of l-NAME inhibited the expression of sensitization to nicotine on day 18; and, l-arginine (1 g/kg) pretreatment reversed this inhibitory effect of l-NAME.Conclusions Our results suggest that NO is implicated in the development and expression of nicotine-induced locomotor sensitization in mice.     

Involvement of central GABA receptors in the regulation of the urinary bladder function of anaesthetized rats

Summary Cystometric recordings were performed in pentobaribitone anaesthetized rats and the effects of gammaaminobutyric acid (GABA) mechanisms on urinary bladder function were evaluated as their influence on a bladder hyperactivity induced by 1-dihydroxyphenylalanine (l-DOPA) after peripheral decarboxylase inhibition. The bladder response was inhibited by intracerebroventricular (i.c.v., 4th ventricle) injections of GABA (250 g), muscimol (0.2 g) and glycine (1,000 g) as well as by systemically administered muscimol (4 mg/kg) and diazepam (2 mg/kg). Intravenous (i.v.) bicuculline, but not i.v. strychnine, antagonized the inhibitory actions of intraperitoneal (i.p.) and i.c.v. muscimol and i.v. diazepam while the opposite was true for the inhibitory action of i.c.v. glycine. In rats not pretreated with l-DOPA, i.p. administration of bicuculline (4 mg/kg) after 15 min caused prominent detrusor contractions that were prevented by an infracollicular brain transection.It is suggested that GABA synapses in the pontinemesencephalic brain region may be involved in the modulation of urinary bladder function.     

Potentiation of the insulin-releasing capacity of tolbutamide by thiols: Studies on the isolated perfused pancreas

Summary It has been suggested that the islet thiol redox status plays a role in the regulation of -cell sensitivity in response to insulin secretagogues. Employing the isolated perfused rat pancreas, the effect of reduced glutathione (1 mM) and L-cysteine (5 mM) on insulin release induced by tolbutamide (0.2 mg/ml), glucose (5.6 and 11.1 mM) and tolbutamide (0.1 mg/ml) in the presence of 5.6 mM glucose was studied.In the absence of glucose or in the presence of 5.6 mM of glucose neither glutathione nor L-cysteine stimulated the release of insulin. Reduced glutathione potentiated the secretion induced by glucose (11.1 mM) during the first and the second phase. L-Cysteine potentiated only the first phase of glucose-induced insulin release, whereas the second phase was depressed. Both of the tested thiols potentiated the insulin secretory action of either tolbutamide (0.2 mg/ml) alone or tolbutamide (01. mg/ml) in the presence of glucose (5.6 mM).The data suggest that supplementation of thiols to the pancreatic -cells perse cannot initiate the insulin secretory process. It is also suggested that GSH and L-cysteine increase the sensitivity of -cells to the stimulatory action of tolbutamide and/or glucose.This study was reported previously and published as an abstract (Abdel-hamid and Ammon 1980)     

Glucose both inhibits and stimulates insulin secretion from isolated pancreatic islets exposed to maximally effective concentrations of sulfonylureas

Summary Isolated pancreatic islets from mice were perifused with media containing maximally effective concentrations of glibenclamide (0.1–10 mol/l) or glipizide (1 mol/l). In these islets an increase of the glucose concentration from 10 mmol/l to 40 mmol/l or addition of d-glyc-eraldehyde (20 mmol/1) caused a temporary decrease in insulin release which was followed by a sustained enhancement of release. -Ketoisocaproate (3 or 20 mmol/1) did not inhibit insulin release; at high concentration it was an even stronger secretagogue than d-glucose or d-glyceraldehyde. It is concluded that high energy phosphates couple B-cell fuel metabolism and insulin release by acting both on the ATP-dependent K⁺ channel and on other targets not yet identified.Some of the results described here are part of the medical thesis of A. WallaschSend offprint requests to U. Panten at the above address     

Peripheral effects of opioid drugs on capsaicin-sensitive neurones of the guinea-pig bronchus and rabbit ear

Summary The effect of a potent opioid agonist, [d-Met², Pro⁵]-enkephalinamide was investigated on two responses involving capsaicin-sensitive afferent neurones, namely, atropine-resistant contractions of the guinea-pig bronchus evoked by electrical field stimulation and the nociceptor stimulation to intraarterial injections of acetylcholine or capsaicin into the vascularly isolated rabbit ear. The hypotheses to be tested were whether (a) opioid receptor activation may inhibit mediator release from primary afferent neurones and (b) the opioid could exert an analgesic effect at a peripheral site of action. Non-cholinergic contractions of the guinea-pig isolated main bronchi due to electrical stimulation were concentration-dependently inhibited by [d-Met², Pro⁵]-enkephalinamide (10 nM–1 M). This effect was abolished by naloxone (1 M). Naloxone alone induced no change in the stimulation-evoked contractions of the bronchus, indicating that no endogenous opioid control was present. Substance P and neurokinin A induced bronchial contractions that were not influenced by [d-Met², Pro⁵]-enkephalinamide. This indicates that [d-Met², Pro⁵]-enkephalinamide inhibits electrically-evoked bronchial contractions by reduced mediator release from capsaicin-sensitive sensory nerve endings, since these contractions are most probably brought about by tachykinins, released from afferent neurones. Capsaicin-induced bronchial contractions were in contrast to electrical stimulation not influenced by [d-Met², Pro⁵]-enkephalinamide which suggests a different site of action. The activation of sensory neurones in the rabbit ear by i. a. injection of acetylcholine and capsaicin was not reduced under infusion of [d-Met², Pro⁵]-enkephalinamide (1 and 10 M) or lofentanil (1 and 10 M). The enhancement of the effect of acetylcholine by infusion of prostaglandin E₂ (0.15 M) also remained unchanged under infusion of 10 M [d-Met², Pro⁵]-enkephalinamide. A peripheral analgesic action of the two opioid agonists studied is therefore not indicated. Send offprint requests to F. Lembeck     

Reversal of the reserpine-induced ptosis by l-threo-3,4-dihydroxy-phenylserine (l-threo-DOPS), a (−)-norepinephrine precursor,and its potentiation by imipramine or nialamide

Summary The effect of l-threo-DOPS on the reserpine-induced ptosis in mice and its modification by imipramine, a norepinephrine (NE) uptake inhibitor, or nialamide, a monoamineoxidase inhibitor, were studied.Intraperitoneal (i.p.) injection of l-threo-DOPS (800 mg/kg) significantly reduced the severity of the ptosis. This reversal of the ptosis by l-threo-DOPS was markedly potentiated by i.p. injection of either imipramine (2.5 mg/kg) or nialamide (30 mg/kg). Response to l-threo-DOPS was also significantly potentiated by intracerebroventricular (i.c.v.) injection of imipramine (10 g). On the other hand, this treatment with imipramine (10 g, i.c.v.) also significantly potentiated the reversal of the ptosis by NE (20 g, i.c.v.), but the reversal by the subcutaneous (s.c.) injection of NE (1 and 3 mg/kg) was not affected.Reserpine (5 mg/kg, i.p.) markedly decreased the brain content of NE in mice, whereas l-threo-DOPS (400 mg/kg, i.p.) slightly restored it. Moreover, by the pretreatment with nialamide (30 mg/kg, i.p.), l-threo-DOPS produced a significant increase in the brain content of NE in reserpinetreated mice.These results suggested that l-threo-DOPS was capable of reversing the reserpine-induced ptosis due to the formation, at least in part of (–)-NE at the synaptic sites of central noradrenergic neurons.     

Intestinal decarboxylation of L-Dopa in relation to dose requirement in Parkinson's disease

Summary The magnitude of the decarboxylation of L-Dopa in the intestinal organs was determined by a method based on oral and intravenous administration of L-3,4-dihydroxyphenylalanine-1-¹⁴C (carboxyl labelled L-Dopa) and analysis of the radioactivity in urine.In 11 parkinsonian patients studied under standardized conditions 74% of L-Dopa given orally as a 0.5 g tablet was decarboxylated in the intestinal organs. Thus less than 26% of the ingested L-Dopa reached the general circulation.The possibility that individual variations in the magnitude of intestinal decarboxylation might be at least partly responsible for the individual variations in the dose requirement of parkinsonian patients was tested. There was neither any correlation between dose requirement of L-Dopa and the intestinal decarboxylation nor between that dose and the plasma disappearance rate of L-Dopa.It is concluded that other factors than those responsible for the peripheral metabolism of L-Dopa determine the individual dose requirement.     

Inhibition of brain dopa-decarboxylase by RO 4-4602 infused ICV blocks alcohol drinking induced in rats by cyanamide

Following the stereotaxic implantation of chronic cannulae for intracerebroventricular (ICV) infusion, rats were given an alcohol preference test to establish their preferred concentration in comparison with water. After alcohol was removed, 15 mg/kg cyanamide was then injected subcutaneously for 4 days in order to maximize volitional intake of single solutions of alcohol, which in these animals ranged from 7 to 15%. The l-dopa-decarboxylase inhibitor benserazide (Ro 4-4602) injected subcutaneously twice daily in doses of 50–100 mg/kg failed to alter the rats' alcohol consumption either in terms of g/kg or proportional values. However, when given ICV twice daily in concentrations of 10 ng–2.0 g per 5.0 l volume, benserazide attenuated the rats' alcohol drinking significantly. This reduction occurred in a dose-dependent manner in terms of both absolute and proportional intakes of alcohol. Pre-treatment of the animals with 1.0 g benserazide given ICV, when alcohol was removed from the test situation, did not abolish the subsequent ingestion of alcohol but its peripheral administration (50 mg/kg) enhanced drinking. These results suggest that the interference with the metabolic pathway of dopamine or serotonin synthesis, possibly through the mechanism of reduced formation of aldehyde adducts in the brain, markedly alters the pattern of voluntary drinking in the rat. Alternatively, benserazide could act by its central inhibition of aldehyde dehydrogenase, which in turn would concomitantly elevate levels of acetaldehyde and thereby reduce alcohol drinking.     

Cyclic GMP stimulation by vasopressin in LLC-PK1 kidney epithelial cells is l-arginine-dependent

Summary The l-arginine antagonist N^G-monomethyl-l-arginine has been shown to inhibit nitric oxide formation from l-arginine in endothelial cells. In the present study N^G-monomethyl-l-arginine was used to assess the role of l-arginine for cyclic GMP stimulation by vasopressin in a kidney epithelial cell line (LLC-PK₁). Preincubation of cells with 1 mol/l, 10 mol/l and 100 mol/l N^G-monomethyl-l-arginine decreased cyclic GMP stimulation at 1 mol/l vasopressin by 25%, 71% and 90%, respectively. This inhibition by N^G-monomethyl-l-arginine was markedly reduced by l-arginine (2 mmol/1) but not d-arginine (2 mmol/1). Cyclic GMP stimulation by the calcium ionophore A23187 was also inhibited by N^G-monomethyl-l-arginine and enantioselectively restored by l-arginine. However, N^G-monomethyl-l-arginine did not affect cyclic GMP stimulation by sodium nitroprusside that spontaneously releases nitric oxide. These results suggest that, in kidney epithelial cells, vasopressin induces nitric oxide formation from l-arginine leading to activation of soluble guanylate cyclase. It is concluded that nitric oxide formation from l-arginine is not only responsible for endothelium-dependent relaxation but may be a more general pathway with regulatory function for intracellular guanylate cyclase activity.Send offprint requests to K. Schror at the above address