Bi-directional actions of estrogen on the renin-angiotensin system

Estrogen stimulates the renin-angiotensin system by augmenting both tissue and circulating levels of angiotensinogen and renin. We show, however, that angiotensin converting enzyme (ACE) activity in the circulation and in tissues is reduced in two animal models of postmenopausal chronic hormone replacement. We observed a reduction of ACE activity in association with a significant increase in plasma angiotensin I (Ang I) and hyperreninemia in ovariectomized monkeys treated with Premarin (conjugated equine estrogen) replacement for 30 months. Plasma angiotensin II (Ang II) levels were not increased in monkeys treated with estrogen, suggesting that the decrease in ACE curtailed the formation of the peptide. The Ang II/Ang I ratio, an in vivo index of ACE activity, was significantly reduced by estrogen treatment, further supporting the biochemical significance of estrogen's inhibition of ACE. In ovariectomized transgenic hypertensive (mRen2)27 rats submitted to estrogen replacement treatment for 3 weeks, ACE activity in plasma and tissue (aorta and kidney) and circulating Ang II levels were reduced, whereas circulating levels of angiotensin-(1-7) (Ang-(1-7) were increased. Ang-(1-7), the N-terminal fragment of Ang II, is a novel vasodilator and antihypertensive peptide. Thus, the net balance of these effects of estrogen on the renin-angiotensin vasoconstrictor/vasodilator system is to promote the antihypertensive effect.

Apoptosis in parasites and parasite-induced apoptosis in the host immune system: a new approach to parasitic diseases

Apoptosis, a form of programmed cell death (PCD), has been described as essential for normal organogenesis and tissue development, as well as for the proper function of cell-renewal systems in adult organisms. Apoptosis is also pivotal in the pathogenesis of several different diseases. In this paper we discuss, from two different points of view, the role of apoptosis in parasitic diseases. The description of apoptotic death in three different species of heteroxenic trypanosomatids is reviewed, and considerations on the phylogenesis of apoptosis and on the eventual role of PCD on their mechanism of pathogenesis are made. From a different perspective, an increasing body of evidence is making clear that regulation of host cell apoptosis is an important factor on the definition of a host-pathogen interaction. As an example, the molecular mechanisms by which Trypanosoma cruzi is able to induce apoptosis in immunocompetent cells, in a murine model of Chagas' disease, and the consequences of this phenomenon on the outcome of the experimental disease are discussed.

Modulation of fibronectin expression in the central nervous system of Lewis rats with experimental autoimmune encephalomyelitis

Fibronectin (FN), a large family of plasma and extracellular matrix (ECM) glycoproteins, plays an important role in leukocyte migration. In normal central nervous system (CNS), a fine and delicate mesh of FN is virtually restricted to the basal membrane of cerebral blood vessels and to the glial limitans externa. Experimental autoimmune encephalomyelitis (EAE), an inflammatory CNS demyelinating disease, was induced in Lewis rats with a spinal cord homogenate. During the preclinical phase and the onset of the disease, marked immunolabelling was observed on the endothelial luminal surface and basal lamina of spinal cord and brainstem microvasculature. In the paralytic phase, a discrete labelling was evident in blood vessels of spinal cord and brainstem associated or not with an inflammatory infiltrate. Conversely, intense immunolabelling was present in cerebral and cerebellar blood vessels, which were still free from inflammatory cuffs. Shortly after clinical recovery minimal labelling was observed in a few blood vessels. Brainstem and spinal cord returned to normal, but numerous inflammatory foci and demyelination were still evident near the ventricle walls, in the cerebral cortex and in the cerebellum. Intense expression of FN in brain vessels ascending from the spinal cord towards the encephalon preceded the appearance of inflammatory cells but faded away after the establishment of the inflammatory cuff. These results indicate an important role for FN in the pathogenesis of CNS inflammatory demyelinating events occurring during EAE.

Expression of extracellular matrix components and their receptors in the central nervous system during experimental Toxoplasma gondii and Trypanosoma cruzi infection

Alterations in extracellular matrix (ECM) expression in the central nervous system (CNS) usually associated with inflammatory lesions have been described in several pathological situations including neuroblastoma and demyelinating diseases. The participation of fibronectin (FN) and its receptor, the VLA-4 molecule, in the migration of inflammatory cells into the CNS has been proposed. In Trypanosoma cruzi infection encephalitis occurs during the acute phase, whereas in Toxoplasma infection encephalitis is a chronic persisting process. In immunocompromised individuals such as AIDS patients, T. cruzi or T. gondii infection can lead to severe CNS damage. At the moment, there are no data available regarding the molecules involved in the entrance of inflammatory cells into the CNS during parasitic encephalitis. Herein, we characterized the expression of the ECM components FN and laminin (LN) and their receptors in the CNS of T. gondii- and T. cruzi-infected mice. An increased expression of FN and LN was detected in the meninges, leptomeninges, choroid plexus and basal lamina of blood vessels. A fine FN network was observed involving T. gondii-free and T. gondii-containing inflammatory infiltrates. Moreover, perivascular spaces presenting a FN-containing filamentous network filled with a4+ and a5+ cells were observed. Although an increased expression of LN was detected in the basal lamina of blood vessels, the CNS inflammatory cells were a6-negative. Taken together, our results suggest that FN and its receptors VLA-4 and VLA-5 might be involved in the entrance, migration and retention of inflammatory cells into the CNS during parasitic infections.

Extracellular matrix molecules play diverse roles in the growth and guidance of central nervous system axons

Axon growth and guidance represent complex biological processes in which probably intervene diverse sets of molecular cues that allow for the appropriate wiring of the central nervous system (CNS). The extracellular matrix (ECM) represents a major contributor of molecular signals either diffusible or membrane-bound that may regulate different stages of neural development. Some of the brain ECM molecules form tridimensional structures (tunnels and boundaries) that appear during time- and space-regulated events, possibly playing relevant roles in the control of axon elongation and pathfinding. This short review focuses mainly on the recognized roles played by proteoglycans, laminin, fibronectin and tenascin in axonal development during ontogenesis.

Diagnosing dementia and normal aging: clinical relevance of brain ratios and cognitive performance in a Brazilian sample

The main objective of the present study was to evaluate the diagnostic value (clinical application) of brain measures and cognitive function. Alzheimer and multiinfarct patients (N = 30) and normal subjects over the age of 50 (N = 40) were submitted to a medical, neurological and cognitive investigation. The cognitive tests applied were Mini-Mental, word span, digit span, logical memory, spatial recognition span, Boston naming test, praxis, and calculation tests. The brain ratios calculated were the ventricle-brain, bifrontal, bicaudate, third ventricle, and suprasellar cistern measures. These data were obtained from a brain computer tomography scan, and the cutoff values from receiver operating characteristic curves. We analyzed the diagnostic parameters provided by these ratios and compared them to those obtained by cognitive evaluation. The sensitivity and specificity of cognitive tests were higher than brain measures, although dementia patients presented higher ratios, showing poorer cognitive performances than normal individuals. Normal controls over the age of 70 presented higher measures than younger groups, but similar cognitive performance. We found diffuse losses of tissue from the central nervous system related to distribution of cerebrospinal fluid in dementia patients. The likelihood of case identification by functional impairment was higher than when changes of the structure of the central nervous system were used. Cognitive evaluation still seems to be the best method to screen individuals from the community, especially for developing countries, where the cost of brain imaging precludes its use for screening and initial assessment of dementia.

The effects of positive end-expiratory pressure on respiratory system mechanics and hemodynamics in postoperative cardiac surgery patients

We prospectively evaluated the effects of positive end-expiratory pressure (PEEP) on the respiratory mechanical properties and hemodynamics of 10 postoperative adult cardiac patients undergoing mechanical ventilation while still anesthetized and paralyzed. The respiratory mechanics was evaluated by the inflation inspiratory occlusion method and hemodynamics by conventional methods. Each patient was randomized to a different level of PEEP (5, 10 and 15 cmH2O), while zero end-expiratory pressure (ZEEP) was established as control. PEEP of 15-min duration was applied at 20-min intervals. The frequency dependence of resistance and the viscoelastic properties and elastance of the respiratory system were evaluated together with hemodynamic and respiratory indexes. We observed a significant decrease in total airway resistance (13.12 ± 0.79 cmH2O l-1 s-1 at ZEEP, 11.94 ± 0.55 cmH2O l-1 s-1 (P<0.0197) at 5 cmH2O of PEEP, 11.42 ± 0.71 cmH2O l-1 s-1 (P<0.0255) at 10 cmH2O of PEEP, and 10.32 ± 0.57 cmH2O l-1 s-1 (P<0.0002) at 15 cmH2O of PEEP). The elastance (Ers; cmH2O/l) was not significantly modified by PEEP from zero (23.49 ± 1.21) to 5 cmH2O (21.89 ± 0.70). However, a significant decrease (P<0.0003) at 10 cmH2O PEEP (18.86 ± 1.13), as well as (P<0.0001) at 15 cmH2O (18.41 ± 0.82) was observed after PEEP application. Volume dependence of viscoelastic properties showed a slight but not significant tendency to increase with PEEP. The significant decreases in cardiac index (l min-1 m-2) due to PEEP increments (3.90 ± 0.22 at ZEEP, 3.43 ± 0.17 (P<0.0260) at 5 cmH2O of PEEP, 3.31 ± 0.22 (P<0.0260) at 10 cmH2O of PEEP, and 3.10 ± 0.22 (P<0.0113) at 15 cmH2O of PEEP) were compensated for by an increase in arterial oxygen content owing to shunt fraction reduction (%) from 22.26 ± 2.28 at ZEEP to 11.66 ± 1.24 at PEEP of 15 cmH2O (P<0.0007). We conclude that increments in PEEP resulted in a reduction of both airway resistance and respiratory elastance. These results could reflect improvement in respiratory mechanics. However, due to possible hemodynamic instability, PEEP should be carefully applied to postoperative cardiac patients.

Gap junctions in cells of the immune system: structure, regulation and possible functional roles

Gap junction channels are sites of cytoplasmic communication between contacting cells. In vertebrates, they consist of protein subunits denoted connexins (Cxs) which are encoded by a gene family. According to their Cx composition, gap junction channels show different gating and permeability properties that define which ions and small molecules permeate them. Differences in Cx primary sequences suggest that channels composed of different Cxs are regulated differentially by intracellular pathways under specific physiological conditions. Functional roles of gap junction channels could be defined by the relative importance of permeant substances, resulting in coordination of electrical and/or metabolic cellular responses. Cells of the native and specific immune systems establish transient homo- and heterocellular contacts at various steps of the immune response. Morphological and functional studies reported during the last three decades have revealed that many intercellular contacts between cells in the immune response present gap junctions or "gap junction-like" structures. Partial characterization of the molecular composition of some of these plasma membrane structures and regulatory mechanisms that control them have been published recently. Studies designed to elucidate their physiological roles suggest that they might permit coordination of cellular events which favor the effective and timely response of the immune system.

Role of sympathetic nervous system and neuropeptides in obesity hypertension

Obesity is the most common cause of human essential hypertension in most industrialized countries. Although the precise mechanisms of obesity hypertension are not fully understood, considerable evidence suggests that excess renal sodium reabsorption and a hypertensive shift of pressure natriuresis play a major role. Sympathetic activation appears to mediate at least part of the obesity-induced sodium retention and hypertension since adrenergic blockade or renal denervation markedly attenuates these changes. Recent observations suggest that leptin and its multiple interactions with neuropeptides in the hypothalamus may link excess weight gain with increased sympathetic activity. Leptin is produced mainly in adipocytes and is believed to regulate energy balance by acting on the hypothalamus to reduce food intake and to increase energy expenditure via sympathetic activation. Short-term administration of leptin into the cerebral ventricles increases renal sympathetic activity, and long-term leptin infusion at rates that mimic plasma concentrations found in obesity raises arterial pressure and heart rate via adrenergic activation in non-obese rodents. Transgenic mice overexpressing leptin also develop hypertension. Acute studies suggest that the renal sympathetic effects of leptin may depend on interactions with other neurochemical pathways in the hypothalamus, including the melanocortin-4 receptor (MC4-R). However, the role of this pathway in mediating the long-term effects of leptin on blood pressure is unclear. Also, it is uncertain whether there is resistance to the chronic renal sympathetic and blood pressure effects of leptin in obese subjects. In addition, leptin also has other cardiovascular and renal actions, such as stimulation of nitric oxide formation and improvement of insulin sensitivity, which may tend to reduce blood pressure in some conditions. Although the role of these mechanisms in human obesity has not been elucidated, this remains a fruitful area for further investigation, especially in view of the current "epidemic" of obesity in most industrialized countries.

Towards understanding the kallikrein-kinin system: insights from measurement of kinin peptides

The kallikrein-kinin system is complex, with several bioactive peptides that are formed in many different compartments. Kinin peptides are implicated in many physiological and pathological processes including the regulation of blood pressure and sodium homeostasis, inflammatory processes, and the cardioprotective effects of preconditioning. We established a methodology for the measurement of individual kinin peptides in order to study the function of the kallikrein-kinin system. The levels of kinin peptides in tissues were higher than in blood, confirming the primary tissue localization of the kallikrein-kinin system. Moreover, the separate measurement of bradykinin and kallidin peptides in man demonstrated the differential regulation of the plasma and tissue kallikrein-kinin systems, respectively. Kinin peptide levels were increased in the heart of rats with myocardial infarction, in tissues of diabetic and spontaneously hypertensive rats, and in urine of patients with interstitial cystitis, suggesting a role for kinin peptides in the pathogenesis of these conditions. By contrast, blood levels of kallidin, but not bradykinin, peptides were suppressed in patients with severe cardiac failure, suggesting that the activity of the tissue kallikrein-kinin system may be suppressed in this condition. Both angiotensin converting enzyme (ACE) and neutral endopeptidase (NEP) inhibitors increased bradykinin peptide levels. ACE and NEP inhibitors had different effects on kinin peptide levels in blood, urine, and tissues, which may be accounted for by the differential contributions of ACE and NEP to kinin peptide metabolism in the multiple compartments in which kinin peptide generation occurs. Measurement of the levels of individual kinin peptides has given important information about the operation of the kallikrein-kinin system and its role in physiology and disease states.

A study of the interaction between Helicobacter pylori and components of the human fibrinolytic system

The interaction of plasminogen, tissue plasminogen activator (t-PA) and urokinase with a clinical strain of Helicobacter pylori was studied. Plasminogen bound to the surface of H. pylori cells in a concentration-dependent manner and could be activated to the enzymatic form, plasmin, by t-PA. Affinity chromatography assays revealed a plasminogen-binding protein of 58.9 kDa in water extracts of surface proteins. Surface-associated plasmin activity, detected with the chromogenic substrate CBS 00.65, was observed only when plasminogen and an exogenous activator were added to the cell suspension. The two physiologic plasminogen activators, t-PA and urokinase, were also shown to bind to and remain active on the surface of bacterial cells. epsilon-Aminocaproic acid caused partial inhibition of t-PA binding, suggesting that the kringle 2 structure of this activator is involved in the interaction with surface receptors. The activation of plasminogen by t-PA, but not urokinase, strongly depended on the presence of cells and a 25-fold enhancer effect on the initial velocity of activation by t-PA compared to urokinase was established. Furthermore, a relationship between cell concentration and the initial velocity of activation was demonstrated. These findings support the concept that plasminogen activation by t-PA on the bacterial surface is a surface-dependent reaction which offers catalytic advantages.

Evidence of muscarinic acetylcholine receptors in the retinal centrifugal system of the chick

In this study we characterize the presence of muscarinic acetylcholine receptors (mAChR) in the isthmo-optic nucleus (ION) of chicks by immunohistochemistry with the M35 antibody. Some M35-immunoreactive fibers were observed emerging from the retinal optic nerve insertion, suggesting that they could be centrifugal fibers. Indeed, intraocular injections of cholera toxin B (CTb), a retrograde tracer, and double-labeling with M35 and CTb in the ION confirmed this hypothesis. The presence of M35-immunoreactive cells and the possible mAChR expression in ION and ectopic neuron cells in the chick brain strongly suggest the existence of such a cholinergic system in this nucleus and that acetylcholine release from amacrine cells may mediate interactions between retinal cells and ION terminals.

The neuroimmune-endocrine axis: pathophysiological implications for the central nervous system cytokines and hypothalamus-pituitary-adrenal hormone dynamics

Cytokines are molecules that were initially discovered in the immune system as mediators of communication between various types of immune cells. However, it soon became evident that cytokines exert profound effects on key functions of the central nervous system, such as food intake, fever, neuroendocrine regulation, long-term potentiation, and behavior. In the 80's and 90's our group and others discovered that the genes encoding various cytokines and their receptors are expressed in vascular, glial, and neuronal structures of the adult brain. Most cytokines act through cell surface receptors that have one transmembrane domain and which transduce a signal through the JAK/STAT pathway. Of particular physiological and pathophysiological relevance is the fact that cytokines are potent regulators of hypothalamic neuropeptidergic systems that maintain neuroendocrine homeostasis and which regulate the body's response to stress. The mechanisms by which cytokine signaling affects the function of stress-related neuroendocrine systems are reviewed in this article.

A comparative study of aging of the elastic fiber system of the diaphragm and the rectus abdominis muscles in rats

In the present study the age-related changes of the striated muscle elastic fiber system were investigated in the diaphragm and rectus abdominis muscles of 1-, 4-, 8- and 18-month-old rats. The activation patterns of these muscles differ in that the diaphragm is regularly mobilized tens of times every minute during the entire life of the animal whereas the rectus abdominis, although mobilized in respiration, is much less and more irregularly activated. The elastic fibers were stained by the Verhoeff technique for mature elastic fibers. Weigert stain was used to stain mature and elaunin elastic fibers, and Weigert-oxone to stain mature, elaunin and oxytalan elastic fibers. The density of mature and elaunin elastic fibers showed a progressive increase with age, whereas the amount of oxytalan elastic fibers decreased in both diaphragm and rectus abdominis muscles and their muscular fascias. These age-related quantitative and structural changes of the elastic fiber system may reduce the viscoelastic properties of the diaphragm and rectus abdominis muscles, which may compromise the transmission of tensile muscle strength to the tendons and may affect maximum total strength.

Determination of macromolecular exchange and PO2 in the microcirculation: a simple system for in vivo fluorescence and phosphorescence videomicroscopy

We have developed a system with two epi-illumination sources, a DC-regulated lamp for transillumination and mechanical switches for rapid shift of illumination and detection of defined areas (250-750 µm²) by fluorescence and phosphorescence videomicroscopy. The system permits investigation of standard microvascular parameters, vascular permeability as well as intra- and extravascular PO2 by phosphorescence quenching of Pd-meso-tetra (4-carboxyphenyl) porphine (PORPH). A Pechan prism was used to position a defined region over the photomultiplier and TV camera. In order to validate the system for in vivo use, in vitro tests were performed with probes at concentrations that can be found in microvascular studies. Extensive in vitro evaluations were performed by filling glass capillaries with solutions of various concentrations of FITC-dextran (diluted in blood and in saline) mixed with different amounts of PORPH. Fluorescence intensity and phosphorescence decay were determined for each mixture. FITC-dextran solutions without PORPH and PORPH solutions without FITC-dextran were used as references. Phosphorescence decay curves were relatively unaffected by the presence of FITC-dextran at all concentrations tested (0.1 µg/ml to 5 mg/ml). Likewise, fluorescence determinations were performed in the presence of PORPH (0.05 to 0.5 mg/ml). The system was successfully used to study macromolecular extravasation and PO2 in the rat mesentery circulation under controlled conditions and during ischemia-reperfusion.