No .NO from NO synthase

The nitric-oxide synthase (NOS; EC 1.14.13.39) reaction is formulated as a partially tetrahydrobiopterin (H4Bip)-dependent 5-electron oxidation of a terminal guanidino nitrogen of L-arginine (Arg) associated with stoichiometric consumption of dioxygen (O2) and 1.5 mol of NADPH to form L-citrulline (Cit) and nitric oxide (.NO). Analysis of NOS activity has relied largely on indirect methods such as quantification of nitrite/nitrate or the coproduct Cit; we therefore sought to directly quantify .NO formation from purified NOS. However, by two independent methods, NOS did not yield detectable .NO unless superoxide dismutase (SOD; EC 1.15.1.1) was present. In the presence of H4Bip, internal .NO standards were only partially recovered and the dismutation of superoxide (O2-.), which otherwise scavenges. .NO to yield ONOO-, was a plausible mechanism of action of SOD. Under these conditions, a reaction between NADPH and ONOO- resulted in considerable overestimation of enzymatic NADPH consumption. SOD lowered the NADPH:Cit stoichiometry to 0.8-1.1, suggesting either that additional reducing equivalents besides NADPH are required to explain Arg oxidation to .NO or that .NO was not primarily formed. The latter was supported by an additional set of experiments in the absence of H4Bip. Here, recovery of internal .NO standards was unaffected. Thus, a second activity of SOD, the conversion of nitroxyl (NO-) to .NO, was a more likely mechanism of action of SOD. Detection of NOS-derived nitrous oxide (N2O) and hydroxylamine (NH2OH), which cannot arise from .NO decomposition, was consistent with formation of an .NO precursor molecule such as NO-. When, in the presence of SOD, glutathione was added, S-nitrosoglutathione was detected. Our results indicate that .NO is not the primary reaction product of NOS-catalyzed Arg turnover and an alternative reaction mechanism and stoichiometry have to be taken into account.

Identification of uterine-related sympathetic neurons in the rat inferior mesenteric ganglion: neurotransmitter content and afferent input

The rat uterus is innervated by sensory and autonomic nerves. Sensory and sympathetic fibers travel in the hypogastric nerves and are associated with the thoracolumbar spinal cord levels T13-L3. The inferior mesenteric ganglion (IMG) contains the somata of sympathetic postganglionic neurons and some of these may project axons to the uterus. Sensory and parasympathetic fibers travel in the pelvic nerve and are associated with the lumbosacral cord levels L6-S1 and pelvic ganglion (PG). We previously reported data concerning the neurochemical anatomy of the PG with regard to the uterine innervation; the present study was undertaken to characterize the neurochemical anatomy of the IMG with regard to it involvement in uterine innervation. A retrograde axonal tracer was used to verify projections of axons of IMG neurons to the uterus. Immunostaining of cryostat sections of the IMG revealed neurons immunoreactive for neuropeptide Y (NPY) and for tyrosine hydroxylase (TH). Immunostaining for the synaptic terminal protein synapsin I (SYN) revealed numerous fine terminals immediately surrounding the principal neurons and in the interneuronal spaces. Varicosities immunoreactive for calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), enkephalin (ENK), substance P (SP) and galanin (GAL) appear to be associated with principal neurons. Additional varicosities stained for nicotinamide adenine dinucleotide phosphate (reduced)-diaphorase (NADPH-d) and nitric oxide synthase (NOS), thus indicating sites of neuronal nitric oxide synthesis. This study revealed that the IMG contains uterine-related neurons and that some of the retrogradely labeled uterine-related neurons contain NPY, TH or both NPY/TH. In addition, uterine-related neurons received abundant afferent inputs indicated by SYN-immunoreactive (-ir) terminals and some of these varicosities labeled for GAL, CGRP, VIP, ENK, or NADPH-d/NOS.

Relation of cholesterol-year score to severity of calcific atherosclerosis and tissue deposition in homozygous familial hypercholesterolemia

The high concentrations of low-density lipoprotein cholesterol in plasma lead to accelerated atherosclerosis in patients homozygous for familial hypercholesterolemia (FH). We addressed the hypothesis that lipid deposition in the arterial vasculature and in nonvascular tissues in these patients correlates with both the duration and severity of their hypercholesterolemia. The severity of calcific atherosclerosis was defined by calcification scores and a calcified volume determined by electron beam tomography. The extent of tendinous xanthomatosis was quantitated by computed tomography. A cholesterol-year score was calculated based on the age and the yearly mean serum cholesterol concentration of each patient. Seventeen patients homozygous for FH were followed up. The average total cholesterol concentration in the study group was 780 +/- 231 mg/dl (20.2 mmol/L), and the cholesterol-year scores ranged from 2,172 mg-year/dl (56 mmol-year/L) to 32,260 mg-year/dl (834 mmol-year/L). Achilles tendon width (r=0.86) and cross-sectional area (r=0.81; both p <0.001) were best correlated with the cholesterol-year score. In addition, the coronary (r=0.61; p<0.05), ostial (r=0.45; p<0.05), and total (r= 0.77; p<0.001) calcification atherosclerosis scores all were best correlated with the cholesterol-year score. Calcific atherosclerosis was not observed in these patients until the cholesterol-year score exceeded 10,000 mg-year/dl (260 mmol-year/L). These findings establish a direct association of cholesterol-year with extravascular lipid deposition in tissues of patients with FH. The cholesterol-year score may be useful in defining the risk of atherosclerosis in patients with more common forms of hypercholesterolemia.

Quantification of lipoprotein(a): comparison of an automated latex-enhanced nephelometric assay with an immunoenzymometric method

Several studies indicate the relevance of lipoprotein(a) (Lp(a)) in the genesis of premature coronary artery disease. A simple method for determining the concentration of Lp(a) is therefore of great interest for assessing the risk of coronary artery disease in patients. We compared a new latex-enhanced immunonephelometric assay (Behringwerke AG, Marburg, Germany), using the Behring Nephelometer System 100, with an established immunoenzymometric assay (Immuno, Heidelberg, Germany). A total of 163 patients was studied. Intra- and inter-assay coefficients of variation were between 2.2% and 7.1%, and between 3.4% and 8.6%, depending on the concentration of Lp(a). The correlation between the studied assays was excellent (r = 0.93, y = 0.98x -1.57, Spearman rank, Passing & Bablok). When values above 1000 mg/l for Lp(a) were excluded, the correlation was even higher. Increased light scattering with particle size, which hitherto has been a disadvantage of the nephelometric technique, seems to be negligible using the improved latex-enhanced approach. In patients with triacylglycerol values above 4.5 mmol/l (n = 19) there was no interference with the Behring system, i.e. the results of the nephelometric method were not increasing, and they agreed with those of the immunoenzymometric assay. In conclusion, this new latex-enhanced nephelometric immunoassay represents a rapid and precise method for the quantification of Lp(a).

NADPH-diaphorase activity in brain macrophages during postnatal development in the rat

NADPH-diaphorase histochemistry, that allows the visualization of cells producing the gaseous intercellular messenger nitric oxide, was used in the study of the forebrain during the first three postnatal weeks in the rat. Subpopulations of NADPH-diaphorase positive neurons were observed at all ages studied. In addition, non-neuronal NADPH-diaphorase-stained cells were detected in the subcortical white matter, and were very numerous in the supraventricular portion of the corpus callosum, and in the internal and external capsules. These cells were present during the first two postnatal weeks, and were especially prominent at the end of the first postnatal week. They were round-shaped and morphologically similar to the brain macrophages, whose phagocytic activity has been shown in previous studies to play a role in naturally occurring cell death and elimination of exhuberant axons. Series of sections adjacent to those stained with NADPH-diaphorase were processed with immunohistochemistry, using two different antibodies (OX-42 and ED-1) that detect macrophagic and microglial markers, and antibodies that recognize the neuronal form of nitric oxide synthase. Furthermore, brain sections from rats at postnatal day 7 were sequentially processed for either OX-42 or nitric oxide synthase immunohistochemistry followed by NADPH-diaphorase histochemistry. The morphological features and distribution of the non-neuronal NADPH-diaphorase-positive cells were superimposable to those obtained with OX-42 and ED-1 immunohistochemistry. In addition, these cells did not display nitric oxide synthase immunoreactivity. Double-labelled NADPH-diaphorase-positive and OX-42-immunoreactive cells were detected at postnatal day 7. The present results show that brain macrophages express NADPH-diaphorase activity during the early stages of the normal postnatal maturation and suggest that nitric oxide produced by brain macrophages could be involved in the development reshaping of the central nervous system.

Hodgkin's disease developing after spontaneous remission of chronic lymphocytic leukemia

We present a 71-year-old patient with chronic lymphocytic leukemia diagnosed 27 years ago. Initially, the disease was staged as Rai II and the patient suffered from secondary immunoglobulin deficiency. Nevertheless, no treatment was necessary at that time. Because of disease progression a single course of chemotherapy was given in 1984. During the following year there was a constant decline of the WBC, accompanied by normalization of the immunoglobulins; both have remained stable ever since that time. However, there was still residual bone marrow infiltration, indicating persisting CLL. In 1993 cervical lymphadenopathy occurred with acute onset. A diagnostic lymphadenectomy revealed Hodgkin's disease of the nodular-sclerosing subtype. The patient was staged as II-III according to the Ann Arbor Classification and underwent radiation therapy. Cytogenetic examination of the bone marrow revealed a normal karyotype with an inversion of chromosome 9. This case demonstrates the rate coincidence of two lymphoproliferative disorders in the same patient. The clinical course and the immunologic findings of this patient are presented, together with a review of the literature.

Thiol dependence of nitric oxide synthase

Nitric oxide synthases (NOS) require NADPH and tetrahydrobiopterin (H4biopterin) to convert L-arginine to L-citrulline. The additional requirement and effects of thiols during purification and activity assays of NOS are unclear; for example, glutathione (GSH) has been reported to stimulate or, in the presence of catalase, to inhibit enzyme activity. We therefore studied the effects of different thiols, thiol reagents, antioxidants, and H4biopterin-regenerating systems on purified porcine cerebellum NOS. GSH in the presence of catalase did not inhibit NOS. In contrast, GSH and, to a lesser degree, several other thiols consistently stimulated total L-arginine turnover up to 4-fold. In the presence of GSH, Vmax of NOS was increased, the usually observed loss of activity during the 15 min assay was less dramatic, and the apparent S0.5 value for H4biopterin decreased. Stabilization of NOS activity by GSH was augmented by protein disulfide isomerase (PDI), indicating that, at least in part, GSH acted by reductive protection of NOS protein thiols. Consistent with this, four different protein thiol reagents abolished NOS activity. In other experiments, specific allosteric binding was excluded as a potential mechanism of GSH regulation of NOS. In addition, GSH may affect NOS kinetics by recycling or preventing the autoxidation of H4biopterin. In support of this, the non-thiol reductant ascorbate and dihydropteridine reductase mimicked the effects of GSH on NOS kinetics, but not on NOS stability. Thus, NOS activity depends on both H4biopterin and the reduced state of essential protein thiols.

Evidence for bidirectional changes in nitric oxide synthase activity in the rat striatum after excitotoxically (quinolinic acid) induced degeneration

Nitric oxide, a gaseous inter- and intracellular messenger, is thought to mediate neurotoxicity via excitatory amino acid receptors which may contribute to the pathogenesis of a variety of neuronal diseases. Excitotoxin lesions induced by quinolinic acid were made unilaterally in the rat striatum to study biochemically, light- and electron microscopically the possible involvement of the nitric oxide synthesizing enzyme nitric oxide synthase in degeneration processes. 5 days after quinolinic acid injection nitric oxide synthase activity in the striatum was elevated to 196.5% (P < 0.005% as compared to controls). There was no requirement of Ca2+ for the enzyme activity measured indicating that the elevation is due to the inducible isoform of nitric oxide synthase. Parallel to the depletion of neurons by quinolinic acid a massive gliosis was seen. Whereas quiescent astroglial cells in the normal striatum did not show any light microscopically detectable nicotinamide adenine dinucleotide phosphate diaphorase reaction, reactive astroglia revealed a substantial labeling distributed over the cell body and their stellar processes. Within the lesion and, particularly, close to the needle tract the number of microglia/macrophages labeled by isolectin B4 increased dramatically. Reactive microglial cells macrophages, situated along the needle tract and characterized by a pseudopodic or a globular shape, contained highest staining activity. At the ultrastructural level only disintegrated, if any, neuronal perikarya were seen five days after quinolinic acid injection while numerous reactive glial cells were observed. Reactive astroglia showed nicotinamide adenine dinucleotide phosphate diaphorase activity by displaying a substantial labeling of the nuclear envelope and endoplasmic membranes. Occasionally stained mitochondria were encountered. Globular-shaped (ameboidal) microglia near the needle tract were rich in phagocytotic debris and, apart from formazan-positive endomembranes, their plasmalemma was often nicotinamide adenine dinucleotide phosphate diaphorase stained. Additionally, in those cells regions of highly electron-dense puncta were seen which differ sharply from other cytoplasmic areas. Such sand-like accumulations of nicotinamide adenine dinucleotide phosphate diaphorase positive grains have never been observed in other cell types, indicating a special type of nitric oxide synthase representation, possibly that of the inducible isoform.

Induction and variants of neuronal nitric oxide synthase type I during synaptogenesis

In the adult central nervous system, nitric oxide (NO) is formed from L-arginine by the so-called constitutive or type I NO synthase (NOS-I155). However, expression of NOS-I155 immunoreactivity and activity was low or not detectable in developing mouse and rat brain. NOS-I155 was sharply induced coincident with the onset of synaptogenesis in specific brain regions. This was followed by a second phase in which total NOS-I155 expression decreased both in specific cell populations and in the total synaptosomal subcellular fraction.Furthermore, two putative variants of NOS-I were transiently observed: an NOS-I-immunoreactive protein with increased electrophoretic mobility (NOS-I144) and a transient hypersensitivity of NOS-I155 to the competitive substrate inhibitor N omega-nitro-L-arginine. It is concluded that NOS-I expression is not constitutive but locally induced. In the central nervous system, this regionally specific, biphasic pattern of postnatal NOS-I induction is consistent with a role for NO in synaptogenesis and synaptic plasticity.

Carboxyl-terminal domain truncation alters apolipoprotein A-I in vivo catabolism

Apolipoprotein A-I (apoA-I), the major protein of high density lipoproteins, facilitates reverse cholesterol transport from peripheral tissue to liver. To determine the structural motifs important for modulating the in vivo catabolism of human apoA-I (h-apoA-I), we generated carboxyl-terminal truncation mutants at residues 201 (apoA-I201), 217 (apoA-I217), and 226 (apoA-I226) by site-directed mutagenesis. ApoA-I was expressed in Escherichia coli as a fusion protein with the maltose binding protein, which was removed by factor Xa cleavage. The in vivo kinetic analysis of the radioiodinated apoA-I in normolipemic rabbits revealed a markedly increased rate of catabolism for the truncated forms of apoA-I. The fractional catabolic rates (FCR) of 9.10 +/- 1.28/day (+/- S.D.) for apoA-I201, 6.34 +/- 0.81/day for apoA-I217, and 4.42 +/- 0.51/day for apoA-I226 were much faster than the FCR of recombinant intact apoA-I (r-apoA-I, 0.93 +/- 0.07/day) and h-apoA-I (0.91 +/- 0.34/day). All the truncated forms of apoA-I were associated with very high density lipoproteins, whereas the intact recombinant apoA-I (r-apoA-I) and h-apoA-I associated with HDL2 and HDL3. Gel filtration chromatography revealed that in contrast to r-apoA-I, the mutant apoA-I201 associated with a phospholipid-rich rabbit apoA-I containing particle. Analysis by agarose gel electrophoresis demonstrated that the same mutant migrated in the pre-beta position, but not within the alpha position as did r-apoA-I. These results indicate that the carboxyl-terminal region (residue 227-243) of apoA-I is critical in modulating the association of apoA-I with lipoproteins and in vivo metabolism of apoA-I.

Colocalization of neuronal nitric oxide synthase with GABA in rat cuneate nucleus

Pre- and post-embedding immunocytochemistry were employed in this electron microscopic investigation of cuneate neurons that are enriched in GABA and in nitric oxide synthase, the enzyme responsible for the synthesis of nitric oxide. GABAergic neurons are local circuit interneurons; 10-20% of them also contain nitric oxide synthase. These are among the smallest GABA-positive perikarya. We describe a network of processes in the rat cuneate nucleus that are immunopositive for nitric oxide synthase. Axon terminals positive for nitric oxide synthase are small and make synapses mainly onto dendrites; they make only occasional axo-axonic contacts. Double-labelling immunocytochemistry verified that the large majority of terminals positive for nitric oxide synthase also contained GABA. However, most GABA-positive profiles were negative for nitric oxide synthase and GABA-positive terminals that are negative for nitric oxide synthase frequently made axo-axonic contacts. These results suggest that nitric oxide synthase is within a specialized subpopulation of interneurons in the cuneate nucleus.

Synaptic interactions between primary afferent terminals and GABA and nitric oxide-synthesizing neurons in superficial laminae of the rat spinal cord

The superficial laminae (I and II) of the spinal dorsal horn receive small caliber primary afferent fibers responsive to noxious stimulation, and contain local circuit neurons that modulate afferent input. Many of these neurons are GABAergic; about a third of these also synthesize nitric oxide. We identified three main morphological types of primary afferent terminals in superficial laminae after injections of a tracer selective for small caliber afferents into the sciatic nerve of rats. The relative densities of the three types varied through the dorsoventral extent of laminae I and II. Synaptic contacts of each type with GABA- and nitric oxide synthase (NOS)-containing dendrites and axon terminals were determined by preembedding and postembedding immunocytochemistry. Nonglomerular primary afferent terminals, likely to originate from peptidergic unmyelinated fibers, were not seen in synaptic contact with either GABA- or NOS-containing neurons. Primary afferent terminals at the center of type 1 glomeruli (C1) and at the center of type 2 glomeruli (C2) are likely to originate from unmyelinated and small myelinated fibers, respectively. GABAergic terminals contacted more C2 than C1 terminals, suggesting more effective presynaptic inhibition of C2 terminals. Many GABAergic terminals were also positive for NOS, but all GABAergic terminals presynaptic to primary afferent terminals were negative for NOS. Only C2 terminals established frequent synapses with NOS-positive dendrites. (ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide nerves in the uterus are parasympathetic, sensory, and contain neuropeptides

Nitric oxide (NO) is synthesized in neurons and is a potent relaxor of vascular and nonvascular smooth muscle. The uterus contains abundant NO-synthesizing nerves which could be autonomic and/or sensory. This study was undertaken to determine: 1) the source(s) of NO-synthesizing nerves in the rat uterus and 2) what other neuropeptides or transmitter markers might coexist with NO in these nerves. Retrograde axonal tracing, utilizing Fluorogold injected into the uterine cervix, was employed for identifying sources of uterine-projecting neurons. NO-synthesizing nerves were visualized by staining for nicotinamide adenine dinucleotide phosphate (reduced)-diaphorase (NADPH-d) and immunostaining with an antibody against neuronal/type I NO synthase (NOS). NADPH-d-positive perikarya and terminal fibers were NOS-immunoreactive (-I). Some NOS-I/NADPH-d-positive nerves in the uterus are parasympathetic and originate from neurons in the pelvic paracervical ganglia (PG) and some are sensory and originate from neurons in thoracic, lumbar, and sacral dorsal root ganglia. No evidence for NOS-I/NADPH-d-positive sympathetic nerves in the uterus was obtained. Furthermore, double immunostaining revealed that in parasympathetic neurons, NOS-I/NADPH-d-reactivity coexists with vasoactive intestinal polypeptide, neuropeptide Y, and acetylcholinesterase and in sensory nerves, NOS-I/NADPH-d-reactivity coexists with calcitonin gene-related peptide and substance P. In addition, tyrosine hydroxylase(TH)-I neurons of the PG do not contain NOS-I/NADPH-d-reactivity, but some TH-I neurons are apposed by NOS-I varicosities. These results suggest NO-synthesizing nerves in the uterus are autonomic and sensory, and could play significant roles, possibly in conjunction with other putative transmitter agents, in the control of uterine myometrium and vasculature.

Aldehyde fixation differentially affects distribution of diaphorase activity but not of nitric oxide synthase immunoreactivity in rat brain

The effect of aldehyde fixation on NADPH- and NADH-dependent diaphorase (d) histochemistry and nitric oxide synthase (NOS) immunocytochemistry in the brain was investigated by comparing the distribution of these enzymes in in situ nitrocellulose blots of unfixed brain sections with that in aldehyde-fixed brain sections. Substitution of NADPH by NADH yielded no gross differences in cellular distribution in the native blot, whereas in fixed sections NADH produced nonspecific staining of the entire section. In the in situ blot NADPHd histochemistry therefore visualized general nitroblue tetrazolium reductase (NBTr) activity, which was particularly strong in hippocampal pyramidal neurons and cerebellar Purkinje cells. Aldehyde fixation abolished the anatomical pattern of general NBTr activity and changed the histochemical distribution in that of the NADPHd activity associated with the distribution of NOS-I immunoreactivity (ir). Fixation intensified NADPHd histochem- ical staining in specific neurons, resulting in outstanding, Golgi-like staining of these neurons in several brain regions, whereas the general NBTr activity in pyramidal and Purkinje cells disappeared. In contrast to the histochemical diaphorase distribution, the distribution of NOS-I ir on blots and in aldehyde-fixed brain sections was similar. No NOS was observed in hippocampal pyramidal and cerebellar Purkinje neurons. In regions like cerebral and cerebellar cortex and striatum the applied anti NOS-I serum had a higher affinity for the native protein. It is concluded that aldehydes, rather than to progressively suppress NOS-unrelated enzymes, differentially elicit NADPHd activity in some groups of neurons while leaving NOS-ir unaffected.

The extravascular contractile system in the human placenta. Morphological and immunocytochemical investigations

In the human placenta, besides the fetal blood vessel system a second extravascular contractile system exists. It is localized in the chorionic plate and runs in a longitudinal direction and adjacent to fetal blood vessels into the stem villi, where it forms perivascular contractile sheaths. Characteristically, cells of the extravascular contractile system are extremely long and spindle-shaped and give rise to fine cell processes, by which they obviously contact each other or insert into the basement membrane of the trophoblast. They show immunoreactivity with desmin, vimentin, alpha-actin, myosin, nitric oxide synthase type I (brain form) and dipeptidyl peptidase IV. The ultrastructure suggests that cells of the extravascular contractile system are related to smooth muscle cells, including subpopulations with myofibroblastic features. In stem villi a few cells are nitric oxide synthase type I immunoreactive. These cells are thought to be specialized smooth-muscle-like cells of the extravascular contractile system or cells of the extravascular contractile system related to paraneurons that generate nitric oxide, which, in turn, may modulate the tone of perivascular contractile sheaths. The high dipeptidyl peptidase IV activity suggests that modulation of the extravascular contractile system may also occur by substance P.

Postnatal development of nitric oxide synthase type 1 expression in the lumbar spinal cord of the rat: a comparison with the induction of c-fos in response to peripheral application of mustard oil

The distribution of the neuronal isoform of the enzyme nitric oxide synthase (type 1) has been investigated in the lumbar spinal cords of neonatal rats (2-20 days old). Large multipolar neurones were present from day 2 around the central canal, in a band across the neck of the dorsal horn and at the thoracic level in the intermediolateral cell column, whereas staining was absent from laminae II. By 20 days the laminae II staining was similar to that found in the adult. NOS expression in lamina II paralleled the development of c-fos expression in this lamina in response to peripheral application of mustard oil.

[Fish eye disease]

A 67-year-old man complained of impaired vision at night for several months. He was known to have arcus senilis (arcus lipoides corneae) since aged 21 years. For the last 20 years both corneas had become progressively more cloudy. His mother was said to have had similar eye changes. Ophthalmological examination discovered no abnormality other than marked corneal dystrophy with hardly separable arcus senilis. General physical examination was normal. Total cholesterol and triglyceride levels in serum were within normal limits, but serum concentration of high density lipoprotein (HDL) cholesterol (8 mg/dl) was reduced as were, within the high density lipoprotein fraction, the concentrations of triglyceride (4 mg/dl), phospholipids (38 mg/dl), the proportion of cholesterol esters (31%), and the cholesterol-esterification rate (51 nmol/ml . h). The HDL-associated activity of lecithin-cholesterol-acetyltransferase activity was scarcely measurable (0.9 nmol/ml . h). The signs in this case (cloudy cornea, marked decrease in serum HDL cholesterol concentration without premature arteriosclerosis) are typical of fish eye disease.

Type I nitric oxide synthase fully accounts for NADPH-diaphorase in rat striatum, but not cortex

The novel gaseous neuromediator nitric oxide is thought to play an important role in development and plasticity. Despite this, gene-knockout mice lacking neuronal (Type I) nitric oxide synthase exhibit relatively normal brain development and behavior. The nervous system of these mice (especially the forebrain) retains some calcium-dependent nitric oxide synthesis, presumably reflecting other isozymes. Type I nitric oxide synthase has NADPH-dependent diaphorase activity. However, this stain also recognizes other isozymes, and it remains controversial whether all diaphorase-positive neurons contain Type I nitric oxide synthase. To assess whether neurons containing another isoform of nitric oxide synthase may be present in the forebrain of normal rodents, we studied co-localization of diaphorase staining with immunocytochemistry for Type I nitric oxide synthase. Co-localization was complete in the striatum, but some neurons deep in cortex were diaphorase-positive and immunonegative, and therefore may contain a splice variant or novel isozyme of nitric oxide synthase.

Expression of nitric oxide synthase immunoreactivity by interstitial cells of the canine proximal colon

A subpopulation of interstitial cells (ICs) are interposed between nerve terminals and smooth muscle cells in the gastrointestinal tract and may participate in neuromuscular transmission. These cells appear to be targets for NO released from enteric inhibitory nerves and respond to exogenous NO with: (i) an elevation in cGMP levels; (ii) an increase in intracellular Ca2+; (iii) and release of a diffusible substance that has tentatively been identified as NO. For the latter to be possible, ICs must express a constitutive isoform of NOS. This study characterized the expression of NOS-like immunoreactivity (NOS-LI) in ICs of the canine colon using 3 antibodies raised against the 2 known constitutive forms of NOS (i.e., neural (nNOS) and endothelial (eNOS) isoforms). Antibodies raised against cNOS and an antibody raised against rat cerebellar nNOS labeled ICs along the submucosal surface of the circular muscle layer (IC-SM), along the surface of septa that separate the circular muscle into fiber bundles (IC-SM), and in the myenteric region between the circular and longitudinal muscle layers (IC-MY). Another antibody raised against rat cerebellar nNOS failed to label ICs. Cultured IC-SM also expressed NOS-LI, suggesting that this feature of the IC phenotype survives culture conditions. Arteriolar endothelial cells in the canine colon were labeled with the same 2 antibodies that labeled ICs, suggesting there are significant structural similarities between NO synthases in ICs and endothelial cells. The data suggest that IC-SM and IC-MY express a constitutive form of NOS. Synthesis of NO by ICs may influence electrical rhythmicity and may serve to amplify and even propagate enteric inhibitory neurotransmission.

Upregulation of neuronal nitric oxide synthase and mRNA, and selective sparing of nitric oxide synthase-containing neurons after focal cerebral ischemia in rat

Nitric oxide synthase-containing neurons are presumed to be resistant to neurodegeneration and neurotoxicity, however this resistance has not been demonstrated after focal cerebral ischemia. We therefore measured the temporal profile of neuronal nitric oxide synthase (NOS-I) mRNA and immunoreactivity and NADPH-diaphorase reactivity over a one week period after permanent middle cerebral artery (MCA) occlusion in 48 male Wistar rats and compared these data to ischemic cell damage as evaluated on hematoxylin and eosin (H & E) stained sections by light microscopy. NOS-I mRNA increased as early as 15 min after MCA occlusion in the ipsilateral striatum and maximal expression of NOS-I was found in the ipsilateral cortex and striatum 1 h after MCA occlusion. The numbers of NOS-I-containing neurons in the ipsilateral cortex and striatum were significantly greater (P < 0.05) than NOS-I-containing neurons in the contralateral hemisphere at 2-48 h after the onset of ischemia. The number of NOS-I-containing neurons peaked at 4 h after MCA occlusion. Neurons exhibited shrinkage or were swollen at 1 to 4 h after MCA occlusion. At 24-48 h after ischemia, neurons in the ischemic lesion appeared to be eosinophilic or ghost like on H & E stained sections. However, some of these neurons retained morphological integrity on the NOS-I immunohistochemical sections. At 168 h after ischemia, all neurons within the lesion appeared necrotic on H & E stained sections; however, scatterred neurons expressed NOS-I and NADPH-diaphorase. The rapid upregulation of NOS-I and mRNA in the ischemic lesion suggests that NOS-I is involved in focal cerebral ischemic injury; the expression of NOS-I by neurons that retain their morphological structure in the area of the infarct suggests that NOS-I-containing neurons are more resistant to the ischemic insult. Our data also indicate a close association of NOS-I immunoreactivity and NADPH-diaphorase reactivity in ischemic brain.

Functional coupling of a Ca2+/calmodulin-dependent nitric oxide synthase and a soluble guanylyl cyclase in vertebrate photoreceptor cells

Electrophysiological recordings on retinal rod cells, horizontal cells and on-bipolar cells indicate that exogenous nitric oxide (NO) has neuromodulatory effects in the vertebrate retina. We report here endogenous NO formation in mammalian photoreceptor cells. Photoreceptor NO synthase resembled the neuronal NOS type I from mammalian brain. NOS activity utilized the substrate L-arginine (Km = 4 microM) and the cofactors NADPH, FAD, FMN and tetrahydrobiopterin. The activity showed a complete dependence on the free calcium concentration ([Ca2+]) and was mediated by calmodulin. NO synthase activity was sufficient to activate an endogenous soluble guanylyl cyclase that copurified in photoreceptor preparations. This functional coupling was strictly controlled by the free [Ca2+] (EC50 = 0.84 microM). Activation of the soluble guanylyl cyclase by endogenous NO was up to 100% of the maximal activation of this enzyme observed with the exogenous NO donor compound sodium nitroprusside. This NO/cGMP pathway was predominantly localized in inner and not in outer segments of photoreceptors. Immunocytochemically, we localized NO synthase type I mainly in the ellipsoid region of the inner segments and a soluble guanylyl cyclase in cell bodies of cone photoreceptor cells. We conclude that in photoreceptors endogenous NO is functionally coupled to a soluble guanylyl cyclase and suggest that it has a neuromodulatory role in visual transduction and in synaptic transmission in the outer retina.

Subpopulations of GABAergic neurons in laminae I-III of rat spinal dorsal horn defined by coexistence with classical transmitters, peptides, nitric oxide synthase or parvalbumin

GABAergic neurons in laminae I-III of the spinal dorsal horn may contain one or more of the following compounds: glycine, acetylcholine, neuropeptide Y, enkephalin, nitric oxide synthase or parvalbumin. Although the pattern of co-localization of some of these compounds is understood, it is not known which types of GABAergic neurons contain parvalbumin, or whether nitric oxide synthase coexists with peptides, acetylcholine or parvalbumin in any of these neurons, and in this study we have used immunocytochemistry and enzyme histochemistry to resolve these issues. Parvalbumin-immunoreactivity was restricted to those GABA-immunoreactive neurons that also showed glycine-immunoreactivity and was not co-localized with neuropeptide Y-immunoreactivity or NADPH diaphorase activity. By combining NADPH diaphorase histochemistry with immunocytochemistry with an antiserum to nitric oxide synthase, we were able to show that NADPH diaphorase activity was a reliable marker for nitric oxide synthase in the spinal cord. Neurons that possess GABA- but not glycine-immunoreactivity may contain neuropeptide Y, enkephalin, acetylcholine or NADPH diaphorase, and all of the cholinergic neurons appear to contain NADPH diaphorase. By combining immunofluorescent detection of neuropeptide Y or enkephalin with NADPH diaphorase histochemistry, we showed that peptide-immunoreactivity did not coexist with NADPH diaphorase. This suggests that neither of these peptides coexists with nitric oxide synthase or with acetylcholine in neurons in the superficial dorsal horn. Several phenotypically distinct groups of GABA-immunoreactive neuron can therefore be identified in laminae I-III of the dorsal horn, and these may represent different functional types of inhibitory neuron.

Nitric oxide synthase expression reveals compartments of cerebellar granule cells and suggests a role for mossy fibers in their development

The developmental expression and cellular distribution of nitric oxide synthase was investigated in the murine cerebellum and in cerebellar neurons developing under controlled in vitro conditions. Cerebellar granule cells expressed nitric oxide synthase only after migration to the internal granule cell layer. Initially, the nascent internal granule cell layer throughout the cerebellum stained uniformly for nitric oxide synthase, but during the second postnatal week, a pattern emerged consisting of clusters of heavily stained granule cells separated by areas of unstained granule cells. This pattern persisted into adulthood. There was a close temporal correlation between innervation of the granule cell layer by mossy fibers and the emergence of granule cell compartments as defined by levels of nitric oxide synthase expression. Granule cells in dissociated cultures derived from cerebellar anlagen prior to mossy fiber innervation also express nitric oxide synthase. The time-course of nitric oxide expression was independent of electrical activity of the neuronal network forming in vitro. However, suppression of spontaneous electrical activity resulted in enhanced nitric oxide synthase expression. These findings indicate that granule cell precursors are endowed with an intrinsic program which regulates nitric oxide synthase induction and which is executed independently of correct positional cues. The data also suggest that electrical activity of ingrowing mossy fibers down regulates nitric oxide synthase expression and plays an important role in the generation of granule cell compartments. These compartments may contribute to the functional organization of the cerebellar cortex.

Co-localization of nitric oxide synthase and NGF receptor in neurons in the medial septal and diagonal band nuclei of the rat

The relationship of neurons that express nitric oxide synthase type I (NOS-I), the synthetic enzyme of the free radical nitric oxide (NO), with cells that contain the low affinity p75 nerve growth factor receptor (NGFr) was examined in the basal forebrain region of the rat using double immunohistofluorescence. NOS and NGFr were found to be co-localized in a neuronal population that displayed a selective distribution. Double immunopositive neurons were evident in the medial septum and in rostral levels of the diagonal band nuclei where the vast majority (more than 80%) of NOS-immunoreactive cells were also NGFr-positive; the two cell populations were separate at more caudal levels of the basal forebrain. These findings support the chemical heterogeneity of septal and basal forebrain neurons which contain NGFr and indicate that in the rat a subset of neurons of the septum-diagonal band complex may release NO.

Immunocytochemical localization of distinct isoforms of nitric oxide synthase in the juxtaglomerular apparatus of normal rat kidney

Nitric oxide (NO) is a messenger molecule that functions as a vasodilator and accounts for the biologic activity of endothelium-derived relaxing factor (EDRF). The enzyme responsible for NO production, NO synthase (NOS), exists in different isoforms. Some are expressed constitutively in various tissues, whereas others require induction by endotoxin and cytokines. There is evidence that NO plays an important role in the regulation of basal renal vascular resistance and in the tubuloglomerular feedback response. Specific antibodies to a constitutive NOS isolated from rat brain (B-NOS) and an inducible NOS isolated from rat aortic smooth muscle (VSM-NOS) were used to establish the cellular and subcellular distribution of NOS in the kidney. Kidneys from normal rats were preserved and processed for light and electron microscopic immunohistochemical studies using both a preembedding and a postembedding horseradish peroxidase technique. By light microscopy, strong immunostaining for B-NOS was observed in the juxtaglomerular apparatus, where it was located in cells of the macula densa. In contrast, immunostaining for VSM-NOS was specifically located in the terminal afferent arteriole and occasionally also in the initial efferent arteriole in the juxtaglomerular apparatus. In addition, faint immunostaining was present in the entire distal tubule. There was no labeling of arcuate or interlobular arteries. The injection of lipopolysaccharide was associated with increased immunostaining for VSM-NOS in the afferent arteriole but had no effect on B-NOS staining. By electron microscopy, B-NOS immunostaining was present throughout the cytoplasm of the macula densa cells, where it appeared to be associated mainly with small vesicles. Immunostaining for VSM-NOS in the afferent arteriole exhibited a patchy distribution in some cells, whereas other cells were stained throughout the cytoplasm. These results indicate that two distinct isoforms of NOS are present in the juxtaglomerular apparatus and support the hypothesis that NOS is involved in the regulation of tubuloglomerular feedback and glomerular capillary pressure.

[In vitro modification of plasma viscosity and erythrocyte aggregation by four plasma substitutes]

We tested the haemorheological effects of the addition of 3.5% oxypolygelatine, 10% dextran 40, 6% dextran 75 or 5% albumin, respectively, to fresh donor blood of 25 healthy young persons. We examined the aggregation and the viscosity of substituent plasma mixtures in such various, but constant volume relations as may be present during intravenous infusion. Albumin reduced viscosity and aggregation, but especially dextran 75 increased both parameters significantly.

[Hemorheologic effects of hydroxyethyl starch 200/0.5, dextran 40, oxypolygelatine and full electrolyte solution over 48 hours]

Four patient groups (n = 28 patients) received in a randomised clinical trial a single intravenous infusion of 500 ml of 10% dextran 40, 3.5% oxypolygelatine, 6% hydroxyethyl starch 200/0.5 or saline solution, respectively. The haemorheological parameters haematocrit, plasma viscosity and erythrocyte aggregation were followed up during 48 hours. In our study oxypolygelatine showed better rheological results than HAES 200/0.5. Dextran 40 especially increased the plasma viscosity and erythrocyte aggregation, so that we cannot recommend this plasma substituent for hypervolemic haemodilution.

Neurons in rat cerebral cortex that synthesize nitric oxide: NADPH diaphorase histochemistry, NOS immunocytochemistry, and colocalization with GABA

Neurons that stain for NADPH diaphorase, which colocalizes with nitric oxide synthase (NOS), are scattered uniformly across neocortex, and denser in entorhinal cortex. In the primary sensorimotor cortex, 0.5-2% of neurons contain NOS. These are most numerous in layers II-III, whereas NOS-positive fibers are concentrated in layers IV and VI. Most stained neurons are aspiny bipolar cells. Some in deep layers are multipolar; very few are pyramidal-shaped. In layer IV, NOS-positive neurons and their dendrites are confined to the septa between barrels. Retrograde tracing experiments demonstrate that NOS-positive cells are local circuit neurons. Double staining demonstrates that NOS-positive neurons also contain GABA.

Nitroxergic autonomic neurones in rat spinal cord

We have used a polyclonal monospecific antibody to rat cerebellum nitric oxide synthase type I (NOS-I, 160 kD) in combination with reduced NADPH-diaphorase histochemical reaction (NADPH-d) to verify colocalization of both NOS protein and NOS enzymatic activity in the rat spinal cord autonomic system. Strong immunoreactivity (IR) of NOS-I was clearly detected in the four main thoracolumbar autonomic nuclei in spinal cord layers of Rexed's laminae VI, VII and X. In all labelled neurones, NOS-I-IR colocalized with NADPH-d activity, suggesting coexistence of brain-specific NOS-I-like protein and its associated enzyme activity. For these neurones the new term 'nitroxergic' (i.e. NO-generating) neurones appears to be justified. Spinal cord nitroxergic neurones are part of a NO-mediated signal transduction pathway for control of the sympathetic 'outflow' to various peripheral target organs.

Nitric oxide synthase immunoreactivity in the rat, mouse, cat and squirrel monkey spinal cord

The distribution of nitric oxide synthase-immunoreactive neurons was examined in the spinal cord of rats, mice, cats and squirrel monkeys at the light microscopic level. Some sections were processed for choline acetyltransferase immunoreactivity. Double-labeling techniques were used to assess possible co-localization of nitric oxide synthase and choline acetyltransferase immunoreactivity in the same spinal neurons. Nitric oxide synthase-immunoreactive neurons were concentrated in three fairly well-defined regions of the spinal cord of all species studied: (i) the intermediolateral cell column of the thoracic and sacral segments, (ii) lamina X of all segments, and (iii) the superficial layers of the dorsal horn of all segments. A few nitric oxide synthase-immunoreactive neurons were scattered in the deeper laminae and the ventral horn. There were fewer nitric oxide synthase-positive neurons in monkey spinal lamina X and dorsal horn than in similar locations of rodents and felines. Double-staining showed that not all choline acetyltransferase-positive neurons in the intermediate cell column and lamina X were nitric oxide synthase-immunoreactive. In the ventral horn, choline acetyltransferase-positive neurons (presumed motoneurons) were nitric oxide synthase-negative. In addition to cell bodies, nitric oxide synthase-positive fibers were scattered in the dorsal, lateral and ventral horns of all species. Finally, punctate nitric oxide synthase-immunoreactive fibers were seen traversing the dorsal, lateral and ventral white matter, and reaching the respective gray matter. The present study shows that, in spite of quantitative differences, the pattern of distribution of nitric oxide synthase-positive neurons in the spinal cord was similar across the four species. The concentration of nitric oxide synthase-positive neurons in the autonomic nuclei and laminae I, II and X of all four species underscores a prominent role of these neurons in visceral and sensory functions.

Neurons in rat hippocampus that synthesize nitric oxide

We studied the distribution and light- and electron-microscopic morphology of neurons in the hippocampal formation containing nitric oxide synthase (NOS), and thus likely to release nitric oxide, a freely diffusible neuromediator implicated in long-term potentiation. Only a small fraction of hippocampal neurons contained NOS or its marker, NADPH diaphorase. Most of the positive neurons were in the pyramidal layer of the subiculum, stratum radiatum of Ammon's horn, and subgranular zone of the dentate gyrus. Positive neurons were also conspicuous in the molecular layer of the dentate gyrus and in the pyramidal layer of CA3, sparse in the pyramidal layer of CA2 and CA1, and almost absent from presubiculum and parasubiculum. Numerous positive fibers were seen, especially in stratum radiatum and stratum lacunosum-moleculare of Ammon's horn. Double staining experiments demonstrated that nearly all NADPH diaphorase-positive neurons in the hippocampus also contained gamma-aminobutyric acid. On the basis of their morphology, distribution, and inhibitory neurotransmitter content, most NOS-positive cells in the hippocampus are probably local circuit neurons. These data suggest that nitric oxide in CA1 may function as a paracrine agent, rather than a spatially precise messenger, in long-term potentiation.

Elevated lipoprotein(a) is lowered by a cholesterol synthesis inhibitor in a normocholesterolaemic patient with premature myocardial infarction

We have identified a 37-year-old patient suffering from two myocardial infarctions, with a markedly elevated lipoprotein(a) [Lp(a)] level and normal levels of cholesterol and triglycerides. Clinically this patient presented with xanthelasma and arcus lipoides corneae. After treatment with a cholesterol synthesis inhibitor (Pravastatin), the Lp(a) concentration in this patient was reduced significantly. This case report supports the hypothesis that elevated Lp(a) is an independent risk factor for coronary artery disease. The effect of the cholesterol synthesis inhibitor on Lp(a) may be due to the upregulation of the LDL-receptor, suggesting a role for LDL receptor in Lp(a) catabolism.

Cloned human brain nitric oxide synthase is highly expressed in skeletal muscle

Complementary DNA clones corresponding to human brain nitric oxide (NO) synthase have been isolated. The deduced amino acid sequence revealed an overall identity with rat brain NO synthase of about 93% and contained all suggested consensus sites for binding of the co-factors. The cDNA transfected COS-1 cells showed significant NO synthase activity with the typical co-factor requirements. Unexpectedly, messenger RNA levels of this isoform of NO synthase was more abundant in human skeletal muscle than human brain. Moreover, we detected high NO synthase activity and the expressed protein in human skeletal muscle by Western blot analysis, indicating a possible novel function of NO in skeletal muscle.

Nitric oxide synthase in macula densa regulates glomerular capillary pressure

Tubular-fluid reabsorption by specialized cells of the nephron at the junction of the ascending limb of the loop of Henle and the distal convoluted tubule, termed the macula densa, releases compounds causing vasoconstriction of the adjacent afferent arteriole. Activation of this tubuloglomerular feedback response reduces glomerular capillary pressure of the nephron and, hence, the glomerular filtration rate. The tubuloglomerular feedback response functions in a negative-feedback mode to relate glomerular capillary pressure to tubular-fluid delivery and reabsorption. This system has been implicated in renal autoregulation, renin release, and longterm body fluid and blood-pressure homeostasis. Here we report that arginine-derived nitric oxide, generated in the macula densa, is an additional intercellular signaling molecule that is released during tubular-fluid reabsorption and counters the vasoconstriction of the afferent arteriole. Antibody to rat cerebellar constitutive nitric oxide synthase stained rat macula densa cells specifically. Microperfusion of the macula densa segment of single nephrons with N omega-methyl-L-arginine (an inhibitor of nitric oxide synthase) or with pyocyanin (a lipid-soluble inhibitor of endothelium-derived relaxation factor) showed that generation of nitric oxide can vasodilate the afferent arteriole and increase glomerular capillary pressure; this effect was blocked by drugs that prevent tubular-fluid reabsorption. We conclude that nitric oxide synthase in macula densa cells is activated by tubular-fluid reabsorption and mediates a vasodilating component to the tubuloglomerular feedback response. These findings imply a role for arginine-derived nitric oxide in body fluid-volume and blood-pressure homeostasis, in addition to its established roles in modulation of vascular tone by the endothelium and in neurotransmission.

Nitric oxide synthase and GABA colocalize in lamina II of rat spinal cord

A dense plexus of fibers in the substantia gelatinosa contains nitric oxide synthase (NOS). Using electron microscopic double-labeling immunocytochemistry for NOS combined with GABA or glutamate, we find that all NOS-positive terminals in this region also contain GABA but are not enriched in glutamate. In an attempt to verify that NOS-positive terminals do not originate from primary afferents, we combined NOS immunocytochemistry with anterograde tracing from the sciatic nerve. An intrinsic spinal origin for the NOS-positive plexus is suggested. The results are discussed in the light of the possible involvement of nitric oxide in hyperalgesia.

Nitric oxide synthase in ferret brain: localization and characterization

1. In the present study, we have investigated the distribution of nitric oxide synthase in the ferret brain. Nitric oxide synthase was determined biochemically and immunochemically. 2. In the rat brain, the highest nitric oxide synthase activity has been detected in the cerebellum. However, in the ferret brain, the highest activity was found in the striatum and the lowest in the cerebellum and cerebral cortex. The enzymatic activity was localized predominantly in the cytosolic fractions, it was dependent on NADPH and Ca2+, and inhibited by NG-nitro-L-arginine or NG-methyl-L-arginine. 3. Western blot analysis revealed that all regions of the ferret brain contained a 160 kD protein crossreacting with an antibody to nitric oxide synthase purified from the rat cerebellum, and the levels of relative intensity of staining by the antibody correlated with the distribution of nitric oxide synthase activity. 4. These results indicate that the ferret brain contains a nitric oxide synthase similar to the rat brain, but the distribution of enzymatic activity in the ferret brain differs markedly from the rat brain.

Mapping of neural nitric oxide synthase in the rat suggests frequent co-localization with NADPH diaphorase but not with soluble guanylyl cyclase, and novel paraneural functions for nitrinergic signal transduction

Nitric oxide synthases (NOS Types I-III) generate nitric oxide (NO), which in turn activates soluble guanylyl cyclase (GC-S). The distribution of this NO-mediated (nitrinergic) signal transduction pathway in the body is unclear. A polyclonal monospecific antibody to rat cerebellum NOS-I and a monoclonal antibody to rat lung GC-S were employed to localize the protein components of this pathway in different rat organs and tissues. We confirmed the localization of NOS-I in neurons of the central and peripheral nervous system, where NO may regulate cerebral blood flow and mediate long-term potentiation. GC-S was located in NOS-negative neurons, indicating that NO acts as an intercellular signal molecule or neurotransmitter. However, NOS-I was not confined to neurons but was widely distributed over several non-neural cell types and tissues. These included glia cells, macula densa of kidney, epithelial cells of lung, uterus, and stomach, and islets of Langerhans. Our findings suggest that NOS-I is the most widely distributed isoform of NOS and, in addition to its neural functions, regulates secretion and non-vascular smooth muscle function. With the exception of bone tissue, NADPH-diaphorase (NADPH-d) activity was generally co-localized with NOS-I immunoreactivity in both neural and non-neural cells, and is a suitable histochemical marker for NOS-I but not a selective neuronal marker.

Nitric oxide synthase immunoreactivity and NADPH-diaphorase activity in a subpopulation of intrinsic neurones of the guinea-pig heart

This is the first report of the presence of nitric oxide synthase (NOS) immunoreactivity and NADPH-diaphorase (NADPH-d) activity in a subpopulation of the intrinsic neurones that innervate the heart. A cytochemical technique to detect NADPH-d and antisera raised against purified rat cerebellar NOS were employed to examine the expression of these enzymes by cells in a dissociated cell culture preparation from newborn guinea-pig atria and interatrial septum. Comparison of the results obtained by these two techniques and double-labelling experiments indicate that a subpopulation of intracardiac neurones contain both NADPH-d and NOS. These results indicate that some intracardiac neurones are capable of synthesizing nitric oxide. This raises the possibility that nitric oxide plays a role in the neural control of the heart.

Colocalization of nitric oxide synthase and NADPH-diaphorase in the myenteric plexus of the rat gut

The pattern of distribution and colocalization of nitric oxide-synthase (NOS) and NADPH-diaphorase in the myenteric plexus of whole-mount preparations of the antrum, duodenum, ileum, caecum, proximal colon and distal colon of the rat were investigated using immunohistochemical and histochemical staining techniques. Almost all the myenteric neurons that were NOS-positive in all regions of the gut examined were also stained for NADPH-diaphorase. However, in the stomach, duodenum and ileum, only a few of the NOS-positive nerve fibres in the tertiary and secondary plexuses and circular muscle layer were also stained for NADPH-diaphorase, whereas in the caecum and distal colon almost all the NOS-positive nerve fibres were also stained for NADPH-diaphorase. The results in the present study are consistent with the view that nitric oxide (NO) has a mediating role in gastrointestinal neurotransmission.

Characterization and localization of nitric oxide synthase in non-adrenergic non-cholinergic nerves from bovine retractor penis muscles

1. Partially purified soluble nitric oxide (NO) synthase was isolated from the bovine retractor penis muscle (BRP), a tissue in which the inhibitory response to non-adrenergic non-cholinergic nerve (NANC) stimulation appears to be mediated by NO or NO-like material. 2. NO synthase from BRP used L-arginine as a substrate, required NADPH, tetrahydrobiopterin, and FAD as co-factors and was Ca2+/calmodulin-dependent. The activity of NO synthase was inhibited by NG-methyl-L-arginine and NG-nitro-L-arginine, and haemoglobin blocked the effect of NO formed by the enzyme. 3. On reducing SDS polyacrylamide gel electrophoresis the apparent molecular mass of NO synthase from BRP was 160 +/- 2 kDa, which is similar to that of the cerebellar NO synthase. Protein immunoblot and immunoprecipitation showed that NO synthase from BRP cross-reacted with the selective antiserum to neuronal NO synthase from rat cerebellum. 4. Immunohistochemistry using the same antiserum demonstrated that NO synthase in BRP was located exclusively within nerve fibres. Thus, autonomic nerves synthesizing the NANC neurotransmitter seem to contain an isoform of NO synthase which is similar to that from rat cerebellum.