Biomedical subjects

A G Herman

Publications and source records attributed to A G Herman.

At least 19 recordsLinked to original sources

PubMed1995

Role of nitric oxide in hyporeactivity to noradrenaline of isolated aortic rings in portal hypertensive rats.

To test the hypothesis that induction of nitric oxide synthase causes systemic vascular hyporesponsiveness to vasopressors in portal hypertension, we performed in vitro experiments on isolated thoracic aortic rings from partial portal vein ligated or sham operated rats at 3 weeks postoperatively. The concentration-response curves to noradrenaline of intact and endothelium-denuded aortic rings from portal hypertensive rats were significantly shifted to the right as compared to those from sham operated animals. Maximal contractions did not significantly differ. Addition of NG-nitro-L-arginine, a specific inhibitor of nitric oxide synthase, shifted the curves to the left in both sham operated and portal hypertensive rats, so that in intact rings, the concentrations of noradrenaline producing half-maximal response did not significantly differ any more between sham operated and portal vein ligated rats. In endothelium-denuded rings, a hyporeactivity to noradrenaline persisted in portal vein ligated rats. Furthermore, NG-nitro-L-arginine induced an additional significant increase in the maximal response to noradrenaline in sham operated as compared to portal hypertensive rats. The endothelium-dependent relaxations to acetylcholine were attenuated in portal hypertensive rats as compared to sham operated animals. From these results, it can be concluded that increased nitric oxide production in the vascular wall of thoracic aorta of portal hypertensive rats is involved in their hyporesponsiveness to noradrenaline. Our findings in endothelium-denuded rings indicate the involvement of the inducible nitric oxide synthase in the smooth muscle layer. Involvement of an inducible nitric oxide synthase in the endothelium cannot be excluded. The endothelial constitutive nitric oxide synthase, however, seems to be suppressed in portal vein ligated rats.

Acetylcholine↗

PubMed1995

Isosorbidedinitrate and SIN-1 as dilators of human coronary arteries and platelet inhibitors.

We compared isosorbidedinitrate (ISDN) and 3-morpholinosydnonimine (SIN-1) as dilators of epicardial coronary arteries and inhibitors of ex vivo platelet aggregation in 23 patients referred for diagnostic coronary arteriography. After completion of the diagnostic study, the patient received graded intravenous (i.v.) infusions (0.5, 1.0, and 1.5 micrograms/kg/min) of either SIN-1 (n = 11) or ISDN (n = 12). Diameters of left anterior descending (LAD) and left ramus circumflex (RCX) coronary arteries were assessed by quantitative digital coronary arteriography before and 5 min after each infusion was started. SIN-1 required an infusion rate of 1.0 micrograms/kg/min to cause dilatation of proximal and middle segments of LAD and RCX. The highest infusion rate caused a modest decrease in mean arterial blood pressure (MAP). In these aspects, SIN-1 was equivalent to ISDN. In addition, blood was collected immediately before treatment and after infusion of the highest dose of ISDN or SIN-1. The sensitivity of platelet-rich plasma (PRP) to ADP and the thromboxane A2 (TXA2) mimetic U-46619 was determined in an aggregometer. The lesser responses to threshold concentrations of ADP and U-46619 and the slight shift in both concentration-response curves indicated that platelets of SIN-1-treated patients were slightly less sensitive to both stimuli as compared with platelets of ISDN-treated subjects. These ex vivo results suggest that SIN-1 may be superior to ISDN as an inhibitor of platelet activation.

Angina Pectoris↗

PubMed1995

Effect of nitric oxide donors on neointima formation and vascular reactivity in the collared carotid artery of rabbits.

Intimal thickening in arteries is considered a site of predilection for atherosclerosis. We investigated whether oral application of the nitric oxide (NO) donors SPM-5185 [N-nitratopivaloyl-S-(N'-acetylalanyl)-cysteine ethylester, 10 mg/kg body weight twice daily (b.i.d.)] and molsidomine (10 mg/kg body weight/day) can retard neointima formation and changes in vascular reactivity induced by a nonocclusive, soft silicone collar positioned around the left carotid artery of rabbits. The contralateral carotid artery was sham operated and served as a control. Drug and placebo (diet without drug) treatments were initiated 7 days before placement of the collar. At the end of the experiments, two segments were cut from each collared and sham-treated artery, one for measurement of the cross-sectional area of intima and media and the other for isometric tension recording. Sham treatment did not result in intimal thickening in either group. In contrast, the intima/media (I/M) ratio was considerably increased after 14 days of collar treatment as a result of neointima formation. Intimal thickening was significantly inhibited by SPM-5185 (I/M ratio 0.05 +/- 0.01 vs. 0.11 +/- 0.02, p < 0.05), but not by molsidomine (0.06 +/- 0.02 vs. 0.08 +/- 0.02, p = 0.49), which is a donor of both NO and superoxide anions. Neither collar nor NO donor treatment altered the area of the media. SPM-5185 did not alter the percentage of replicating smooth muscle cells (SMC) in the media after collar treatment, as demonstrated by their immunoreactivity for proliferating cell nuclear antigen (PCNA).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1995

Sequential induction of nitric oxide synthase by Corynebacterium parvum in different organs of the mouse.

1. The ability of Corynebacterium parvum (C. parvum) to induce nitric oxide (NO) synthase in the macrophage, spleen, liver, aorta, heart and brain, and to elevate plasma NO2-/NO3- in the mouse was investigated. In addition, the relationship between NO synthase activity and blood pressure was studied. 2. C. parvum (100 mg kg-1, i.p.) induced a time-dependent expression of a Ca(2+)-independent NO synthase in the macrophage, spleen, liver, aorta and heart. The time course of induction of the NO synthase varied such that the maximum enzyme activity was at day 8 in the macrophage and liver, day 12 in the spleen and heart and day 16 in the aorta. 3. There was no significant induction of a Ca(2+)-independent NO synthase in the brain, nor was there any change in the Ca(2+)-dependent enzyme in this organ, during the study period. 4. C. parvum produced a gradual decrease in blood pressure, with a maximum fall at day 16 (from 108 +/- 1 mmHg to 79 +/- 3 mmHg), which recovered gradually by day 28. 5. Plasma NO2-/NO3- was significantly elevated between days 8 and 24, with a maximum increase at day 12. 6. These results show that C. parvum induces a Ca(2+)-independent NO synthase in a number of tissues and that this induction occurs initially in macrophages and the liver. This suggests that induction of the NO synthase in the other tissues is secondary and probably the result of activation of macrophages and some cells of the liver. 7. Furthermore, the decrease in blood pressure induced by C. parvum is associated with the induction of NO synthase in the vasculature, whereas the increased concentration of plasma NO2-/NO3- seems to result from the generation of NO by a number of tissues.

Amino Acid Oxidoreductases↗

PubMed1995

Human and rat macrophages mediate fungistatic activity against Rhizopus species differently: in vitro and ex vivo studies.

Both rat alveolar macrophages and a human macrophages cell line with characteristics of human tissue (e.g., alveolar) macrophages (THP-1) were found to inhibit the germination of Rhizopus spores. However, the conditions under which fungistatic activity occurs are different for these two cell types. The inhibition of Rhizopus spore germination by rat alveolar macrophages requires the activation of macrophages and the presence of serum and L-arginine. During rat alveolar macrophage-mediated fungistatic activity, L-arginine is oxidized to nitric. Human macrophage-mediated fungistatic activity is similar to that mediated by rat macrophages in terms of the serum requirement, but it does not require L-arginine. Human macrophages did not produce any nitrite detectable by the colorimetric assay. Their ability to inhibit germination was enhanced by the combination of endotoxin and gamma interferon. The inhibition of Rhizopus spore germination by rat alveolar macrophages is thus mediated by the generation of nitric oxide, whereas the mechanism of similar inhibition by human macrophages remains poorly understood. Serum samples from diabetic rats as well as from patients with diabetes or uremia decreased the inhibitory effect of macrophages on spore germination. Dialysis of the serum samples against a buffered salt solution antagonized this phenomenon, indicating that a low-molecular-weight factor in the sera of patients with diabetes or uremia may modulate local antifungal defense mechanisms. The absence of L-arginine-dependent nitrogen oxidation in human macrophages, compared with its presence in rat alveolar macrophages, under conditions during which fungistatic activity occurs suggests that this phenomenon is species specific.

Animals↗

PubMed1994

Effect of potassium channel blockade and alpha 2-adrenoceptor activation on the release of nitric oxide from non-adrenergic non-cholinergic nerves.

1. Using a superfusion bioassay cascade, we studied the effect of K+ channel blockers and alpha 2-adrenoceptor agents on the release of a transferable factor, previously characterized as nitric oxide (NO) or a nitric oxide-related substance (NO-R), in response to non-adrenergic non-cholinergic (NANC) nerve stimulation in the canine ileocolonic junction (ICJ). 2. The non-selective K+ channel blockers, 4-aminopyridine (4-AP, 50 microM) and tetraethylammonium (TEA, 1 mM) and the more selective blocker of Ca(2+)-activated K+ channels, charybdotoxin (Leiurus quinquestriatus venom (LQV), 0.4 microgram ml-1), significantly enhanced the release of NO-R induced by low frequency stimulation (2-4 Hz). In the presence of 4-AP and TEA, the release of NO-R was nearly abolished by tetrodotoxin (2 microM), and by L-NG-nitroarginine (L-NOARG, 0.1 mM). Relaxations induced by direct injection of exogenous NO (5-50 pmol) or nitroglycerin (GTN, 10-30 pmol) onto the rabbit aortic detector ring were not affected. 3. The alpha 2-adrenoceptor agonist, UK-14,304 (0.3 microM) inhibited the release of NO-R induced by low (2-4 Hz), but not that induced by high (16 Hz), frequency stimulation. This inhibitory effect was completely reversed by the alpha 2-adrenoceptor antagonist, yohimbine (0.3 microM). Neither UK-14,304 nor yohimbine affected the relaxations induced by exogenous NO (5 pmol) or GTN (10 pmol) on the aortic detector ring.3+

4-Aminopyridine↗

PubMed1994

Vasoconstrictor responses after neo-intima formation and endothelial removal in the rabbit carotid artery.

1. The present study examined the responses of the rabbit carotid artery to five vasoconstrictors after neo-intima formation induced by perivascular collar treatment and evaluated the role of constitutive and inducible nitric oxide (NO) synthase and endothelial cells (ECs). 2. Ring segments of the rabbit carotid artery were mounted in organ chambers for isometric tension recording. Neo-intima-bearing vessels developed less force (Emax) in response to KCl, the thromboxane-mimetic U-46619 and 5-hydroxytryptamine (5-HT), but not to angiotensin I and II. 3. The collar-treatment increased the sensitivity to 5-HT, and decreased the sensitivity to angiotensin II. The sensitivity to U-46619 and angiotensin I remained unchanged. 4. Mechanical removal of ECs and inhibition of NO biosynthesis by NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine (L-NOARG) increased the sensitivity to 5-HT in sham and collar-treated segments to the same extent. The effects of collar-treatment and endothelial removal or treatment with inhibitors of NO biosynthesis were additive. Inhibition of NO biosynthesis failed to augment sensitivity to 5-HT after endothelial denudation. L-NOARG increased the force development to KCl in sham and collar-treated segments to the same extent. However, L-NMMA and L-NOARG failed to augment the contractile responses of neo-intima-bearing vessels to 5-HT and KCl after endothelial removal. 5. The responses to angiotensin I were not altered, either by the neo-intima or by endothelial removal. In arteries with a neo-intima the sensitivity to angiotensin II was decreased. Removal of the endothelium or incubation with L-NOARG counteracted this rightward shift and increased Emax.6. Our results demonstrate that contractions to 5-HT, angiotensin II and KCl are modulated by NO in both sham and neo-intima-bearing vessels. Inhibition of NO biosynthesis and collar treatment resulted in additive effects on the EC50 values, suggesting that the 5-HT and angiotension (AT) receptors on the smooth muscle cells are also modified by the formation of a neo-intima. Furthermore, the reduced contractile responses of segments with a neo-intima are not due to NO formed by an inducible NO synthase in those vessels.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1992

Synergism between interleukin-1 beta and interferon-gamma, an inducer of nitric oxide synthase, in rat lung fibroblasts.

An L-arginine-dependent pathway, by which L-arginine is metabolised to citrulline and nitrogen oxides, has been recently identified in some cell types. In cultured rat lung fibroblasts the presence of L-arginine was necessary for the production of nitrite to be induced by rat recombinant interferon-gamma and synergistically enhanced by lipopolysaccharide and interleukin-1 beta. Lipopolysaccharide and interleukin-1 beta did not induce nitrite biosynthesis by themselves. Biosynthesis was apparently dependent on tetrahydrobiopterin, since it could be blocked by diaminohydroxypyrimidine, an inhibitor of tetrahydrobiopterin synthesis. Dexamethasone blocked nitrite production by a receptor-mediated mechanism. These data indicate that rat lung fibroblasts express an L-arginine-dependent nitric oxide synthase which can be induced by some mediators of inflammation.

Amino Acid Oxidoreductases↗

PubMed1992

Differences in structure of angiotensin-converting enzyme inhibitors might predict differences in action.

Angiotensin-converting enzyme (ACE) inhibitors probably work by inhibition of tissue-located ACE, and they differ with regard to their relative ability to inhibit ACE in different organs. This apparent tissue selectivity may stem from either differences in tissue bioavailability or from a different affinity for the enzyme. The affinity of the ACE inhibitor for a particular enzyme is not only determined by the structure of the inhibitor, but also by the structure of the enzyme. ACE enzymes from different tissues may be slightly different, and this may have some bearing on the relative affinities of different ACE inhibitors for ACE from different tissues. The duration of inhibition in a particular tissue reflects not only the affinity of that inhibitor for the tissue enzyme, but also reflects the ease or difficulty with which the active ACE inhibitor is released from that tissue. Whether the beneficial effects of ACE inhibitors on experimentally induced myocardial infarction and reperfusion arrhythmias are due to the presence of a sulfhydryl group or are mainly related to the ACE inhibitor-mediated bradykinin potentiation remains a matter of controversy.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1992

Soybean trypsin inhibitor and beta-amylase induce alveolar macrophages to release nitrogen oxides.

Rat alveolar macrophages incubated with soybean trypsin inhibitor and beta-amylase produced nitrite in a dose- and time-dependent manner. This production depends on the presence of L-arginine (L-arg) in the culture medium. The precursor of this nitrite was demonstrated as being nitric oxide by bleaching ferredoxin at 410 nm when added to the culture medium. NG-Monomethyl-L-arginine and the tetrahydrobiopterin biosynthesis inhibitor 2,4-diamino-6-hydroxypyrimidine inhibited the release of nitrite in a dose-dependent manner. Dexamethasone was able to modulate this release. These data indicate that alveolar macrophages are capable of secreting L-arg-derived nitrogen oxides when stimulated with certain alimentary proteins.

Animals↗

PubMed1992

Diminished capacity to release metabolites of nitric oxide synthase in macrophages loaded with oxidized low-density lipoproteins.

Activation of J774-macrophages with lipopolysaccharide (LPS) or LPS and recombinant interferon-gamma (IFN-gamma) induced nitric oxide (NO) synthase activity, as measured by the production of nitrite and citrulline. NO synthase activity was suppressed by loading the cells with oxidatively modified low-density lipoprotein (ox-LDL) but not with acetylated LDL (ac-LDL), although the intracellular lipid accumulation was comparable. This suggests that the extent of activation of lipid-loaded macrophages may be influenced by the type of lipid.

Amino Acid Oxidoreductases↗

PubMed1992

Impaired endothelium-dependent cholinergic coronary vasodilation in patients with angina and normal coronary arteriograms.

The coronary vasomotor responses to selective infusion of graded concentrations (10(-6) to 10(-4) M) of acetylcholine into the left anterior descending artery were assessed by quantitative coronary arteriography in 24 patients with normal coronary arteriograms (12 patients with atypical symptoms and 12 patients with typical anginal pain) and 36 patients with coronary artery disease with different degrees of atherosclerosis of the left anterior descending artery. In the patients with normal coronary arteries and atypical chest pain, acetylcholine induced predominantly a vasodilator response, which was maximal during a 10(-5) M acetylcholine infusion. In contrast, in patients with coronary artery disease, acetylcholine caused dose-dependent vasoconstriction, which was observed even if the left anterior descending artery itself was smooth. Marked vasoconstriction was also induced in the patients with typical anginal pain and angiographically normal coronary arteries. In nine of these patients, this constrictor response was associated with anginal pain and electrocardiographic evidence of myocardial ischemia. Intracoronary administration of isosorbide dinitrate (1 mg) relieved the anginal pain and dilated all vessels. These data suggest that 1) patients with normal coronary arteriograms and angina pectoris manifest impairment of endothelium-dependent vasodilation similar to that observed in patients with overt coronary atherosclerosis; and 2) abnormal coronary vasoconstrictor responses resulting from this impairment may contribute to the pathogenesis of myocardial ischemia and angina in these patients.

Acetylcholine↗

PubMed1992

Improved endothelial viability of heart valves cryopreserved by a new technique.

The aim of this study was to compare different techniques of aortic valve cryopreservation by studying the viability of the endothelial cells. Viability was assessed by measuring their in vitro prostacyclin (PGI2) production under basal and stimulated conditions. Fresh and cryopreserved porcine valves were incubated at 37 degrees C in tissue culture medium and PGI2 content in the medium was measured every 15 min up to 300 min. Cryopreservation by the older procedure A included 5% fetal calf serum (FCS) in the preservation medium, a plastic box inside a freezing plastic bag, a cooling schedule approximating -2 degrees C/min, a long thawing time and few dilution steps of the cryoprotectant dimethylsulphoxide (DMSO). The newer procedure B differed from A in packaging, freezing and thawing rates and DMSO dilution. Procedure C was similar to B with the exception that FCS was omitted. Leaflets preserved by procedure A produced significantly less prostacyclin as compared to those treated according to procedures B or C. We conclude that minor differences in the cryopreservation method can become critical to endothelial functional viability.

Animals↗

PubMed1992

Interleukin 8 (IL-8) in the bronchoalveolar lavage fluid from patients with the adult respiratory distress syndrome (ARDS) and patients at risk for ARDS.

A sensitive and specific radioimmunoassay was used to measure interleukin 8 (IL-8) in bronchoalveolar lavage fluids from control subjects, patients with the adult respiratory distress syndrome (ARDS) and patients undergoing coronary bypass surgery, a risk factor for developing ARDS. Concentrations of IL-8, albumin, total protein and numbers of neutrophils were higher in both patient groups than in controls. Levels of IL-8 were significantly correlated with the influx of neutrophils, plasma protein extravasation and with the PaO2/FiO2 ratio. These data suggest that IL-8 may mediate the recruitment of neutrophils from the vascular compartment into the alveolar space and may therefore be an important determinant in neutrophil-mediated lung injury. Since increased levels of IL-8 were also found in BAL fluid from patients at risk in whom ARDS did not develop, other factors are likely to be involved and IL-8, as well as other markers of inflammation, are of little prognostic use.

Adult↗

PubMed1992

Paradoxical vasoconstriction as result of acetylcholine and serotonin in diseased human coronary arteries.

UNLABELLED: In experimental atherosclerosis, impairment of endothelium-dependent vasodilation results in an unmasking of potent vasoconstrictor responses to serotonin, a substance released by aggregating platelets. To determine whether similar changes occur in diseased human coronary arteries, the responses to selective intracoronary infusions of acetylcholine and serotonin (both endothelium-dependent vasodilators) and to isosorbide dinitrate (a dilator directly acting on the smooth muscle) were assessed by quantitative coronary arteriography in 16 patients with angiographically normal coronary arteries, in 10 patients with minimal (less than 30% narrowing) and in five patients with more advanced (greater than 50% narrowing) coronary atherosclerosis. Acetylcholine induced constriction in diseased coronary arteries, but in patients with normal coronary arteriograms, it caused dilatation in seven patients (smooth dilators) and constriction in nine patients (smooth constrictors). In the smooth dilators, however, serotonin evoked no significant changes (+1.4 +/- 4.1%), whereas in the smooth constrictors and in patients with diseased coronary arteries, serotonin caused dose-dependent constriction. The vasoconstrictor responses to serotonin were similar in patients with minimal (-26.5 +/- 4.7%) and more advanced atherosclerosis (-30.9 +/- 5.3%). In one patient with coronary artery disease, serotonin caused a temporary coronary occlusion. All other patients dilated in response to isosorbide dinitrate. The vasomotor responses to acetylcholine and to serotonin were thus shown to be completely in parallel. CONCLUSION: impairment of endothelium-dependent vasodilation unmasks potent vasoconstrictor responses to serotonin both in early and advanced coronary atherosclerosis. These changes may play an important role in the pathogenesis of a dynamic coronary artery stenosis.

Acetylcholine↗

PubMed1992

Selective muscarinic alterations of nitric oxide-mediated relaxations by neointima.

During neointima formation, which is an early and essential step in the development of atherosclerosis, endothelium-independent relaxations (nitroglycerin, 3-morpholinosydnonimine) are preserved, whereas muscarinic endothelium-dependent relaxation becomes impaired. The present study was undertaken to determine the selectivity of this impairment. The neointima was induced by positioning a nonocclusive, soft silicone collar around the left carotid artery of rabbits. The contralateral artery served as a control. Seven days later, vascular rings were mounted in organ chambers, contracted with phenylephrine (0.35 microM), and cumulative dose-relaxation curves were made. Intima-bearing vessels were less sensitive to acetylcholine, confirming the original observation. In contrast, the dose-relaxation curves for substance P and for the calcium ionophore A23187 were not altered in the presence of neointima. The curve for ATP was even shifted to the left. These results suggest that the nitric oxide synthase: cyclic GMP system remains intact in intima-bearing vessels and that the diminished endothelium-dependent relaxations are due to a selective alteration of the muscarinic receptors.

Adenosine Triphosphate↗

PubMed1992

The role of endothelial cells in the relaxations induced by 13-hydroxy- and 13-hydroperoxylinoleic acid in canine arteries.

1. One of the major fatty acids in the arterial wall is linoleic acid. It has been shown that its 13-hydroxy metabolite (13-HODE) is generated in significant amounts by cultured endothelial cells. The aim of the present study was to investigate the relaxations to 13-HODE and its hydroperoxyprecursor (13-HPODE) and to examine the role of the endothelial cells. 2. Ring segments of canine circumflex and splenic artery were mounted in organ chambers for isometric tension recording. During contractions induced by prostaglandin F2 alpha or noradrenaline, 13-HODE and 13-HPODE evoked dose-dependent relaxations. Removal of the endothelial cells reduced the relaxations to 13-HODE, but had no effect on those elicited by 13-HPODE. 3. Indomethacin and meclofenamate (0.3 microM to 30 microM) blocked the relaxations evoked by 13-HODE and 13-HPODE in endothelium-denuded rings. In segments with endothelium, both cyclo-oxygenase inhibitors again abolished the relaxations to 13-HODE, but only diminished those to 13-HPODE. 4. Prostacyclin biosynthesis, as measured by radioimmunoassay, increased upon incubation with 13-HODE and 13-HPODE (10 microM). Bioassay of the release of nitric oxide (NO) indicated that NO was not involved in the relaxations elicited by either metabolite. Moreover, L-NG-nitroarginine (100 microM), a specific inhibitor of NO synthesis, did not influence the relaxations to 13-HODE and 13-HPODE. The responses to 13-HPODE were also not altered by superoxide dismutase. 5. In the splenic artery 13-HPODE and 13-HODE induced contractions above 3 microM which were blocked by the thromboxane receptor antagonist, daltroban.In the circumflex artery contractile responses to high concentrations of 13-HODE could be observed only after inhibition of cyclo-oxygenase.6. We conclude that the vasodilatation induced by 13-HODE and 13-HPODE was due to stimulation of prostacyclin biosynthesis both in the endothelium and smooth muscle cells or other subendothelial structures. An additional, unidentified intermediate, which was neither NO nor a cyclo-oxygenase product nor superoxide anion, contributed to the relaxations to 13-HPODE in arteries with endothelium.

Animals↗

PubMed1992

Pterins inhibit nitric oxide synthase activity in rat alveolar macrophages.

1. The synthesis of nitrite and citrulline from L-arginine by immune-stimulated rat alveolar macrophages and the modulation of this synthesis were studied. 2,4-Diamino-6-hydroxypyrimidine (DAHP), 6R-5,6,7,8-tetrahydro-L-biopterin (BH4) and L-sepiapterin were potent inhibitors of the recombinant interferon-gamma induced production of nitrogen oxides in intact cultured cells with I50 values for BH4 and L-sepiapterin of approximately 10 microM. They were equally effective in inhibiting the induced production of citrulline. This inhibitory effect was concentration-dependent for all three modulators investigated. 2. The inhibitory effects were not dependent on incubation times of either 24 or 48 h, on the immune-stimulus used (lipopolysaccharide, interferon-gamma), or whether these stimuli were added during or after the induction period. 3. Pterin-6-carboxylic acid (PCA), which cannot be converted into BH4, and methotrexate (MTX), which inhibits dihydrofolatereductase but not de novo biosynthesis of BH4, did not change the production of nitrite. 4. The data indicate that DAHP, an inhibitor of the de novo biosynthesis of the co-factor BH4, blocks the nitric oxide synthase activity in intact cells. Since the pterins BH4 and L-sepiapterin blocked the L-arginine dependent production of nitrite and citrulline, the activity of nitric oxide synthase in phagocytic cells may be regulated by metabolic endproducts of the de novo biosynthesis of BH4.

Amino Acid Oxidoreductases↗