Rhesus prophylaxis--history and current status]

The essential problem of the vicious circle leading to end-stage cardiovascular disease is atherosclerosis. This paper focuses on the functional changes centred on the endothelium that accompany the development of atherosclerosis, examining in particular pathological alterations in the L-arginine/nitric oxide (NO) pathway. Changes in the NO system are associated with altered platelet and monocyte interactions with the vessel wall, abnormal vasoconstriction and altered vascular structure. Diabetes, hyperglycaemia, hypertension and hypercholesterolaemia are all involved in this process. Endothelin is a vasoconstrictor peptide produced by endothelial cells which is upregulated under these conditions. Normalising endothelial function could involve platelet inhibition, lipid-lowering agents to prevent foam cell formation and decrease the lipid load of the blood vessel wall, and agents to interfere with some of the mechanisms involved in vasoconstriction, proliferation and migration, including ACE-inhibitors and angiotensin receptor antagonists, and possibly new tools such as endothelin receptor antagonists.     

Differential regulation of cytokine production by nitric oxide

Nitric oxide (NO) has recently been identified as a potent and pleiotropic intracellular mediator produced by and acting on many cells of the body. Although considerable attention has been devoted to the regulation of NO by inflammatory cytokines, and also to the role of NO as an important effector molecule in immune function, there is very little information on the role of this mediator in modulating T-cell-dependent cytokine production. In this study we show that physiological levels of NO (either produced by activated macrophages or by the addition of exogenous NO donors) can selectively down-regulate interleukin-3 (IL-3) production by spleen cells from contact-sensitized mice, while leaving IL-2 activity unaffected. Thus NO may have an important role as an immunomodulatory as well as effector molecule in the immune system.     

Gaseous transmitters and neuroendocrine regulation

Recent work has demonstrated that the brain has the capacity to synthesize impressive amounts of the gases nitric oxide (NO) and carbon monoxide (CO). There is growing evidence that these gaseous molecules function as novel neural messengers in the brain. This article reviews the pertinent literature concerning the putative role of NO and CO as critical neurotransmitters and biological mediators of the neuroendocrine axis. Abundant evidence is presented which suggests that NO has an important role in the control of reproduction due to its ability to control GnRH secretion from the hypothalamus. NO potently stimulates GnRH secretion and also appears to mediate the action of one of the major transmitters controlling GnRH secretion, glutamate. Evidence is presented which suggests that NO stimulates GnRH release due to its ability to modulate the heme-containing enzyme, guanylate cyclase, which leads to enhanced production of the second messenger molecule, cGMP. A physiological role for NO in the preovulatory LH surge was also evidenced by findings that inhibitors and antisense oligonucleotides to nitric oxide synthase (NOS) attenuate the steroid-induced and preovulatory LH surge. CO may also play a role in stimulating GnRH secretion as heme molecules stimulate GnRH release in vitro, an effect which requires heme oxygenase activity and is blocked by the gaseous scavenger molecule, hemoglobin. Evidence is also reviewed which suggests that NO acts to restrain the hypothalamic-pituitary-adrenal (HPA) axis, as it inhibits HPA stimulation by various stimulants such as interleukin-1 beta, vasopressin, and inflammation. This effect fits a proinflammatory role of NO as it leads to suppression of the release of the anti-inflammatory corticosteroids from the adrenal. Although not as intensely studied as NO, CO has been shown to suppress stimulated CRH release and may also function to restrain the HPA axis. Evidence implicating NO in the control of prolactin and growth hormone secretion is also reviewed and discussed, as is the possible role of NO acting directly at the anterior pituitary. Taken as a whole, the current data suggest that the diffusible gases, NO and CO, act as novel transmitters in the neuroendocrine axis and mediate a variety of important neuroendocrine functions.     

Overproduction of nitric oxide in pathophysiology of blood vessels

Sustained production of large amounts of nitric oxide (NO) is induced in blood vessels by inflammatory stimuli as a result of the expression of the inducible form of NO-synthase (NOS-2). This happens in systemic inflammatory reactions like septic shock and in local reactions produced by endothelium denudation and atherosclerosis. NOS-2 activity in blood vessels may protect tissues by virtue of the vasodilating, anti-thrombotic and leukocyte adhesion inhibitory effects of NO. It may also participate in vascular remodeling as a result of the antiproliferative and pro-apoptotic actions of NO. However excessive production of NO in blood vessels is involved in circulatory failure that takes place in systemic inflammatory reactions and it may be cytotoxic for surrounding tissues. For these reasons, inhibition of NO overproduction has been proposed in the treatment of septic shock. Selective inhibitors of NOS-2 activity or NO trapping agent, or both, might prove to be valuable drugs in the treatment of some inflammatory diseases. The conditions in which NO shifts from a tissue protective to a damaging role are not well elucidated. Recent findings suggest that the interactions with superoxide radicals, thiols, and metals (particularly with Fe2+) may be important not only in buffering excess NO produced by NOS-2, but also in channeling it from physiologically to pathophysiologically relevant targets. It has also been found recently that adventitial cells may play an important part in vascular NO production and generation of NO stores in the media layer. The ultimate effect of NO in blood vessels might depend on its site of production, local concentration, and interactions with other tissue components.     

Neuroendocrine perspectives on social attachment and love

The purpose of this paper is to review existing behavioral and neuroendocrine perspectives on social attachment and love. Both love and social attachments function to facilitate reproduction, provide a sense of safety, and reduce anxiety or stress. Because social attachment is an essential component of love, understanding attachment formation is an important step toward identifying the neurobiological substrates of love. Studies of pair bonding in monogamous rodents, such as prairie voles, and maternal attachment in precocial ungulates offer the most accessible animal models for the study of mechanisms underlying selective social attachments and the propensity to develop social bonds. Parental behavior and sexual behavior, even in the absence of selective social behaviors, are associated with the concept of love; the analysis of reproductive behaviors, which is far more extensive than our understanding of social attachment, also suggests neuroendocrine substrates for love. A review of these literatures reveals a recurrent association between high levels of activity in the hypothalamic pituitary adrenal (HPA) axis and the subsequent expression of social behaviors and attachments. Positive social behaviors, including social bonds, may reduce HPA axis activity, while in some cases negative social interactions can have the opposite effect. Central neuropeptides, and especially oxytocin and vasopressin have been implicated both in social bonding and in the central control of the HPA axis. In prairie voles, which show clear evidence of pair bonds, oxytocin is capable of increasing positive social behaviors and both oxytocin and social interactions reduce activity in the HPA axis. Social interactions and attachment involve endocrine systems capable of decreasing HPA reactivity and modulating the autonomic nervous system, perhaps accounting for health benefits that are attributed to loving relationships.     

Diffusion of nitric oxide and scavenging by blood in the vasculature

It has been deduced (Lancaster, Proc. Natl. Acad. Sci. USA 91 (1994) 8137-8141), from a consideration of Fick's law of diffusion, that the very effective scavenging of nitric oxide (NO) by haemoglobin in red blood cells prevents any NO from endothelial cells migrating outwards into vascular smooth muscle. This conclusion has led some authors to suggest that endothelium-derived relaxing factor (EDRF) is not free NO. We have reconsidered the application of Fick's law to the migration of NO in the vasculature, making allowance for the reaction of NO with guanylate cyclase and for the layer of red blood-free plasma next to the endothelium. The source of NO is taken as an infinite cylinder. Calculations for vessels of various diameters indicate that a substantial amount of NO migrates outwards in spite of very effective scavenging by haemoglobin and that the relative amount of NO migrating outwards depends upon the radius of the vessel. The view that locally produced NO is not responsible for vascular dilation has not been sustained.     

Anterograde signaling by nitric oxide: characterization and in vitro reconstitution of an identified nitrergic synapse

Nitric oxide (NO) is recognized as a signaling molecule in the CNS where it is a candidate retrograde neurotransmitter. Here we provide direct evidence that NO mediates slow excitatory anterograde transmission between the NO synthase (NOS)-expressing B2 neuron and an NO-responsive follower neuron named B7nor. Both are motoneurons located in the buccal ganglia of the snail Lymnaea stagnalis where they participate in feeding behavior. Transmission between B2 and B7nor is blocked by inhibiting NOS and is suppressed by extracellular scavenging of NO. Furthermore, focal application of NO to the cell body of the B7nor neuron causes a depolarization that mimics the effect of B2 activity. The slow interaction between the B2 and B7nor neurons can be re-established when the two neurons are cocultured, and it shows the same susceptibility to NOS inhibition and NO scavenging. In cell culture we have also examined spatial aspects of NO signaling. We show that before the formation of an anatomical connection, the presynaptic neuron can cause depolarizing potentials in the follower neuron at distances up to 50 micro(m). The strength of the interaction increases when the distance between the cells is reduced. Our results suggest that NO can function as both a synaptic and a nonsynaptic signaling molecule.     

Physiological and physiopathological aspects of nitric acid in mammalian tissues

In recent years, nitric oxide (NO), a single but highly reactive molecule has become known as the central point of many researchs. NO is synthesized by the enzyme nitric oxide synthase (NOS) in mammals from the amino-acid L-arginine. The products of L-arginine oxidation by NOS are L-citrulline and NO. Nitric oxide has a very short half life, is lipid soluble, reacts easily with several enzymatic systems, and is produced by a wide amount of cells. At least, three kinds of enzymes NOS have been described: two of them are calcium-dependent and continuously present in select cells (constitutive NOS, cNOS). One cNOS isoform is present in the cytosol of neuronal cells, while the other isoform is present in membrane-bound form, in endothelial cells. cNOS produces small quantities of NO, following stimulation by specific agonist. NO produced by cNOS frequently mediates cellular communications and cellular signaling. A third isoform is calcium-independent, is not present in unstimulated cells, and produces large quantities of NO following stimulation of the appropriate cell with cytokines or LPS (inducible NOS, iNOS). NO is a mediator of both physiological and pathological process. It acts directly on its targets, one of them, maybe the most important, is the soluble guanylate cyclase, and produces a variety of biological effects, ranged from cytoprotection to cytotoxicity. An analysis of the biochemistry and physiology of NO is the focus of this review, together with its biological action and potential therapeutical implications.     

Oral reconstruction using the peroneal flap

1. Recent studies have indicated that nitric oxide (NO) production in the kidney contributes to the regulation of renal haemodynamics and excretory function. Inhibition of nitric oxide synthase (NOS) reduces renal blood flow by approximately 25% and markedly reduces sodium excretion without reductions in filtered load. In particular, inhibition of NO synthesis markedly suppresses the slope of the arterial pressure-mediated response in sodium excretion. 2. Further studies have shown that constant intrarenal infusion of a NO donor in dogs treated with a NOS inhibitor produced diuretic and natriuretic responses but failed to restore the slope of the pressure-induced natriuretic response. These data indicate that an alteration in intrarenal NO activity, rather than the simple presence of NO during changes in arterial pressure is required for full expression of pressure natriuretic responses. 3. In support of the hypothesis that NO is involved in the mediation of pressure natriuresis, we also recently demonstrated a direct relationship between changes in arterial pressure and urinary excretion rate of sodium as well as nitrate and nitrite (a marker for endogenous NO activity) in the presence of efficient autoregulation of cortical and medullary blood flow. 4. The direct inhibitory actions of NO on tubular sodium reabsorption have also been observed in cultured tubular cells as well as isolated, perfused cortical collecting duct segments. 5. Thus, the collective data suggest that acute changes in arterial pressure induce changes in intrarenal NO production, which may directly alter tubular reabsorptive function to manifest the phenomenon of pressure natriuresis.     

Neuroendocrine properties of adrenocortical cells

Recent data suggest that adrenocortical cells under pathological as well as under physiological conditions show neuroendocrine properties. Within the normal adrenal, this neuroendocrine differentiation seems to be restricted to cells of the zona glomerulosa and might be important for an autocrine regulation of adrenocortical function. In addition, such neuroendocrine differentiation is a common phenomenon in adrenocortical carcinomas and is therefore of clinical importance. In our studies, the expression of neuronal cell adhesion molecule (NCAM) could be shown in the zona glomerulosa of the normal human adrenal and in the human adrenocortical cell line NCI-H295 that also produces synaptophysin, a synaptic vesicle associated protein. In this chapter, data on neuroendocrine characteristics of adrenocortical cells are summarized and discussed.     

Effect of a nitric oxide synthase inhibitor, S-ethylisothiourea, on cultured cells and cardiovascular functions of normal and lipopolysaccharide-treated rabbits

Nitric oxide (NO) is synthesized from L-arginine by three isoforms of NO synthase (NOS). It is essential to suppress the function of the inducible isoform (macNOS) for amelioration of some inflammatory diseases in which the cytotoxic effect of NO is involved. S-Ethylsiothiourea (S-EIU) was reported to be a potent and specific inhibitor of macNOS. We also confirmed that it rather specifically inhibited the activity of the purified macNOS and the formation of nitrite by RAW264.7 cells compared to NG-monomethyl-L-arginine (L-NMA) and NG-nitro-L-arginine (L-NNA), the other isoforms being less effective. S-EIU suppressed the release of nitrite and lactate dehydrogenase from rat vascular smooth muscle cells treated with interleukin-1 beta and forskolin more potently than L-NMA or L-NNA. S-EIU also slightly suppressed internucleosomal DNA cleavage in pancreatic beta-cells induced by NO produced by macNOS. Intravenous administration of either S-EIU at 0.1 mg/kg/min or L-NMA at 1 mg/kg/min increased the blood pressure but decreased the heart rate in normal rabbits, while aminoguanidine at 1 mg/kg/min affected neither cardiovascular function. These inhibitors at these doses caused recovery of the blood pressure in lipopolysaccharide-treated rabbits that exhibited lowered blood pressure similar to that in the case of septic shock. Although S-EIU seemed not to be an adequate inhibitor for therapeutic use in vivo due to its side effects on cardiovascular functions, it is one of the most potent inhibitors of macNOS among reported inhibitors in vitro.     

A randomized trial to assess the efficacy of surgery in addition to radiotherapy in patients with a single cerebral metastasis

1. A comparison of the effects of dietary and genetically-induced hypercholesterolaemia on the vasodilator and antiaggregatory capacity of the endothelium was made in rabbit isolated subclavian artery rings. 2. Dietary-induced hypercholesterolaemia in NZW rabbits decreased the maximum relaxation to carbachol (0.01-10 microM) and calcimycin (0.01-0.1 microM) in vessel rings precontracted with 5-hydroxytryptamine (5-HT), 0.1 microM), when compared to responses observed in rings obtained from control normocholesterolaemic NZW rabbits. The relaxant responses to SIN-1 (3-(4-morpholinyl)-sydnonimine hydrochloride) were attenuated but were not significantly different from controls. In Froxfield genetically hypercholesterolaemic (FHH) rabbits, the maximum relaxations to carbachol, calcimycin and SIN-1 were all reduced significantly. 3. Neither genetic nor dietary-induced hypercholesterolaemia modified the contractile responses of vessel rings to either KCl (10-100 mM) or 5-HT (0.01-10 microM). 4. Endothelium-dependent inhibition of collagen-induced platelet aggregation in whole blood was demonstrated by stimulation of a vessel ring, incorporated into the blood sample, with carbachol (10 microM, final blood concentration). This effect was inhibited by NG-nitro-L-arginine (L-NOARG, 100 microM). SIN-1 (10 microM, final blood concentration) also decreased whole blood platelet aggregation, but only in the presence of an unstimulated vessel ring, and this was unaffected by L-NOARG. Superoxide dismutase (150 u ml-1) did not influence the inhibition of aggregation by either a carbachol-stimulated vessel ring or by SIN-1. 5. Carbachol-stimulated artery rings from FHH rabbits inhibited platelet aggregation to a similar extent to that seen with rings from control normocholesterolaemic rabbits. Rings from hypercholesterolaemic NZW rabbits, however, did not significantly inhibit platelet aggregation when stimulated with carbachol. SIN-1 inhibited platelet aggregation in the presence of rings from either group of hypercholesterolaemic rabbits. 6. Hypercholesterolaemia induced by dietary modification induces changes in endothelial function which are characteristically different from those seen in genetically hypercholesterolaemic rabbits. It appears that dietary-induced hypercholesterolaemia primarily decreases NO release from the endothelium, while in genetically-induced hypercholesterolaemic vessel rings NO is released but there is a decreased responsiveness of the vascular smooth muscle cells to NO. This may reflect differences in the age and severity of the atherosclerotic lesions in the two groups of rabbits.     

Lipopolysaccharide a virulence factor of Helicobacter pylori: effect of antiulcer agents

Following its benchmark discovery, nitric oxide (NO) is now known to play important functional roles in a variety of physiological systems. Within the vasculature, NO induces vasodilation, inhibits platelet aggregation, prevents neutrophil/platelet adhesion to endothelial cells, inhibits smooth muscle cell proliferation and migration, regulates programmed cell death (apoptosis) and maintains endothelial cell barrier function. NO generated by neurons acts as a neurotransmitter, whereas NO generated by macrophages in response to invading microbes acts as an antimicrobial agent. Because neurons, blood vessels and cells of the immune system are integral parts of the reproductive organs, and in view of the important functional role that NO plays in those systems, it is likely that NO is an important regulator of the biology and physiology of the reproductive system. Indeed, in the past 10 years, NO has established itself as a polyvalent molecule which plays a decisive role in regulating multiple functions within the female as well as the male reproductive system. This review provides an overview of the role of NO in various reproductive organs under physiological and pathological conditions.     

Nitric oxide mediates angiogenesis in vivo and endothelial cell growth and migration in vitro promoted by substance P

We evaluated the effects of nitric oxide (NO) generators and endogenous production of NO elicited by substance P (SP) in the angiogenesis process. Angiogenesis was monitored in the rabbit cornea in vivo and in vitro by measuring the growth and migration of endothelial cells isolated from coronary postcapillary venules. The angiogenesis promoted in the rabbit cornea by [Sar9]-SP-sulfone, a stable and selective agonist for the tachykinin NK1 receptor, and by prostaglandin E1 (PGE1), was potentiated by sodium nitroprusside (SNP). Conversely, the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME), given systemically, inhibited angiogenesis elicited by [Sar9]-SP-sulfone and by PGE1. Endothelial cells exposed to SNP exhibited an increase in thymidine incorporation and in total cell number. Exposure of the cells to NO generating drugs, such as SNP, isosorbide dinitrate, and glyceryl trinitrate, produced a dose-dependent increase in endothelial cell migration. Capillary endothelial cell proliferation and migration produced by SP were abolished by pretreatment with the NO synthase inhibitors N omega-mono-methyl-L-arginine (L-NMMA), N omega-nitro-L-arginine (L-NNA), and L-NAME. Exposure of the cells to SP activated the calcium-dependent NO synthase. Angiogenesis and endothelial cell growth and migration induced by basic fibroblast growth factor were not affected by NO synthase inhibitors. These data indicate that NO production induced by vasoactive agents, such as SP, functions as an autocrine regulator of the microvascular events necessary for neovascularization and mediates angiogenesis.     

The beta adrenoreceptor antagonist, nipradilol, preserves the endothelial nitric oxide response in atherosclerotic vessels of rabbit

We evaluated the effects of nipradilol, a beta-adrenoreceptor antagonist which contains a nitroxy residue, for vascular response in atherosclerosis of rabbits. Four groups of rabbits received different diets (standard diet; standard diet plus 10 mg/kg/day nipradilol; atherogenic diet [standard diet plus 1% cholesterol]; atherogenic diet plus 10 mg/kg/day nipradilol) for 9 weeks. Plasma lipids, blood pressure, vascular function, nitric oxide (NO), activity of NO synthase, cGMP, and histological atherosclerotic changes were evaluated. Neither the atherogenic diet nor nipradilol treatment affected significantly the animals' body weight, blood pressure, or heart rate. The atherogenic diet increased total cholesterol and triglycerides, which were not altered by nipradilol. The atherogenic diet diminished the acetylcholine-induced NO mediated relaxation. Nipradilol treatment restored this relaxation. Analyses using a NO-sensitive selective electrode showed that nipradilol released NO in the presence of cells and that NO release was greater in atherosclerotic aorta with than without nipradilol treatment. Nipradilol treatment increased the basal NO release as evaluated by the aortic tissue cyclic GMP (cGMP) levels in atherosclerotic vessel, and reduced the esterified cholesterol levels in atherosclerotic vessel. Conclusively, NO released by nipradilol may protect endothelium derived relaxation in atherosclerotic vessels, and may partially inhibit the accumulation of cholesterol in the atherosclerotic lesions.     

Effects of local geometry and fluid dynamics on regional platelet deposition on artificial surfaces

An important aspect of blood-material interactions is the activation, adhesion, and subsequent aggregation of blood platelets on the artificial surface, all of which are directly affected by local fluid dynamics. The objective of this work was to directly correlate changing local fluid dynamic conditions produced by various vessel geometries, including stenosis, aneurysm, and separate contraction and expansion geometries, with quantitative in vitro measurements of regional platelet deposition. We directly measured platelet deposition as a function of axial position along four Lexan flow chambers with axisymmetric models of these geometries using 111In-labeled platelets. Platelet deposition was maximum in observed areas of flow recirculation and reattachment and minimum in locations of high shear and separation. For the stenosis geometry, two distinct regions of increased platelet deposition were apparent, one proximal to and one distal to the stenosis throat. An approximately linear increase in platelet densities was produced in the aneurysm region, increasing in the direction of flow. Through a comparison of platelet deposition with local fluid streamline orientation, we have shown that platelet deposition is increased in certain areas due to the enhanced convective transport of platelets and blood cells to the vessel wall along locally curved streamlines with velocity components perpendicular to the vessel wall.     

Apoptosis and expression of inducible nitric oxide synthase are mutually exclusive in renal mesangial cells

Nitric oxide (NO) is a multipurpose messenger molecule, important for blood vessel relaxation, neuronal communication, and antimicrobial activities. The generation of NO from L-arginine is catalyzed by NO synthase (NOS). An inducible form of NOS, iNOS, was first characterized in macrophages and then in many other tissues and cells, including renal mesangial cells. Mesangial cells play a crucial role in the regulation of the glomerular filtration rate as well as in the pathophysiology of certain forms of glomerulonephritis in which mesangial cells and macrophages produce NO in high amounts. Because reports have associated NO production with apoptotic cell death in macrophages and we recently demonstrated NO-mediated apoptosis in mesangial cells, we searched for the relationship between in situ iNOS induction and apoptosis by iNOS immunocytochemistry and terminal desoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. RAW 264.7 macrophages exhibited homogeneous iNOS expression and apoptotic nuclei in the iNOS-containing cells upon stimulation with interferon-gamma and lipopolysaccharide. In contrast, stimulated rat mesangial cells stained heterogeneously for iNOS, depending on cell passage and iNOS-stimulating pathway. Mesangial cells expressing iNOS did not display signs of apoptosis and, vice versa, cells showing characteristic features of apoptosis did not stain for iNOS. Thus, our study suggests that mesangial cells react to stimulation by interleukin-1 and/or cAMP-elevating compounds with mutually exclusive responses, either by expression of iNOS or by undergoing programmed cell death.     

Nitric oxide in cerebral ischemic neurodegeneration and excitotoxicity

The observation that the free radical nitric oxide (NO) acts as a cell signaling molecule in key physiological processes such as regulation of blood pressure and immunological host-defense responses is probably one of the most important and exciting findings made in biology in the last decade. Likewise, in the brain NO has been implicated in a number of fundamental processes, including memory formation, sexual behavior and the control of cerebral blood flow. This has radically altered the accepted dogma of brain physiology and has placed NO at the center stage of neuroscience research. Evidence suggests that some of the actions of NO in the brain may be intimately linked to those of the classic excitatory neurotransmitter glutamate. The historical view that aberrations in glutamate signal transduction may underlie central neurodegeneration following, for example, cerebral ischemia, has implicated NO, by default, as a potential mediator of neuronal death. Indeed, with the advent of potent and specific compounds that interact with NO synthesizing (NOS) enzymes and with the NO signaling cascade, there is now ample evidence to suggest that NO can mediate neurodegeneration, although its involvement is paradoxical. Its cerebrovascular effects may act to limit ischemic damage by preserving tissue perfusion and preventing platelet aggregation, while NO produced in the parenchyma, either directly following the ischemic insult or at a later stage as part of a neuroinflammatory response, may be deleterious to the outcome of ischemia. Nonetheless, significant efforts are made into the potential therapeutic use of chemical NO donors and specific NOS inhibitors in the treatment of cerebral ischemia and other central neurodegenerative disorders. Here, the latest concepts and developments in our understanding of the role of NO in cerebral ischemic neurodegeneration are discussed.