Location and secretion of brain angiotensinogen

The Renin Angiotensin System as a Therapeutic Target in Traumatic Brain Injury

Traumatic brain injury (TBI) is a major public health problem, with limited pharmacological options available beyond symptomatic relief. The renin angiotensin system (RAS) is primarily known as a systemic endocrine regulatory system, with major roles controlling blood pressure and fluid homeostasis. Drugs that target the RAS are used to treat hypertension, heart failure and kidney disorders. They have now been used chronically by millions of people and have a favorable safety profile. In addition to the systemic RAS, it is now appreciated that many different organ systems, including the brain, have their own local RAS. The major ligand of the classic RAS, Angiotensin II (Ang II) acts predominantly through the Ang II Type 1 receptor (AT1R), leading to vasoconstriction, inflammation, and heightened oxidative stress. These processes can exacerbate brain injuries. Ang II receptor blockers (ARBs) are AT1R antagonists. They have been shown in several preclinical studies to enhance recovery from TBI in rodents through improvements in molecular, cellular and behavioral correlates of injury. ARBs are now under consideration for clinical trials in TBI. Several different RAS peptides that signal through receptors distinct from the AT1R, are also potential therapeutic targets for TBI. The counter regulatory RAS pathway has actions that oppose those stimulated by AT1R signaling. This alternative pathway has many beneficial effects on cells in the central nervous system, bringing about vasodilation, and having anti-inflammatory and anti-oxidative stress actions. Stimulation of this pathway also has potential therapeutic value for the treatment of TBI. This comprehensive review will provide an overview of the various components of the RAS, with a focus on their direct relevance to TBI pathology. It will explore different therapeutic agents that modulate this system and assess their potential efficacy in treating TBI patients.

The proteome of the human endolymphatic sac endolymph

The endolymphatic sac (ES) is the third part of the inner ear, along with the cochlea and vestibular apparatus. A refined sampling technique was developed to analyse the proteomics of ES endolymph. With a tailored solid phase micro-extraction probe, five ES endolymph samples were collected, and six sac tissue biopsies were obtained in patients undergoing trans-labyrinthine surgery for sporadic vestibular schwannoma. The samples were analysed using nano-liquid chromatography-tandem mass spectrometry (nLC-MS/MS) to identify the total number of proteins. Pathway identification regarding molecular function and protein class was presented. A total of 1656 non-redundant proteins were identified, with 1211 proteins detected in the ES endolymph. A total of 110 proteins were unique to the ES endolymph. The results from the study both validate a strategy for in vivo and in situ human sampling during surgery and may also form a platform for further investigations to better understand the function of this intriguing part of the inner ear.

Serum proteomic analysis of novel predictive serum proteins for neurological prognosis following cardiac arrest

Early prognostication of neurological outcome in comatose patients after cardiac arrest (CA) is vital for clinicians when assessing the survival time of sufferers and formulating appropriate treatment strategies to avoid the withdrawal of life‐sustaining treatment (WLST) from patients. However, there is still a lack of sensitive and specific serum biomarkers for early and accurate identification of these patients. Using an isobaric tag for relative and absolute quantitation (iTRAQ)‐based proteomic approach, we discovered 55 differentially expressed proteins, with 39 up‐regulated secreted serum proteins and 16 down‐regulated secreted serum proteins between three comatose CA survivors with good versus poor neurological recovery. Then, four proteins were selected and were validated via an enzyme‐linked immunosorbent assay (ELISA) approach in a larger‐scale sample containing 32 good neurological outcome patients and 46 poor neurological outcome patients, and it was confirmed that serum angiotensinogen (AGT) and alpha‐1‐antitrypsin (SERPINA1) were associated with neurological function and prognosis in CA survivors. A prognostic risk score was developed and calculated using a linear and logistic regression model based on a combination of AGT, SERPINA1 and neuron‐specific enolase (NSE) with an area under the curve of 0.865 (P < .001), and the prognostic risk score was positively correlated with the CPC value (R = 0.708, P < .001). We propose that the results of the risk score assessment not only reveal changes in biomarkers during neurological recovery but also assist in enhancing current therapeutic strategies for comatose CA survivors.

Role of the Renin Angiotensin System in Blood Pressure Allostasis-induced by Severe Food Restriction in Female Fischer rats

Severe food restriction (FR) is associated with blood pressure (BP) and cardiovascular dysfunction. The renin-angiotensin system (RAS) regulates BP and its dysregulation contributes to impaired cardiovascular function. Female Fischer rats were maintained on a control (CT) or severe FR (40% of CT) diet for 14 days. In response to severe FR, BP allostasis was achieved by up-regulating circulating Ang-[1–8] by 1.3-fold through increased angiotensin converting enzyme (ACE) activity and by increasing the expression of AT₁Rs 1.7-fold in mesenteric vessels. Activation of the RAS countered the depressor effect of the severe plasma volume reduction (≥30%). The RAS, however, still underperformed as evidenced by reduced pressor responses to Ang-[1–8] even though AT₁Rs were still responsive to the depressor effects of an AT₁R antagonist. The aldosterone (ALDO) response was also inadequate as no changes in plasma ALDO were observed after the large fall in plasma volume. These findings have implications for individuals who have experienced a period(s) of severe FR (e.g., anorexia nervosa, dieters, natural disasters) and suggests increased activity of the RAS in order to achieve allostasis contributes to the cardiovascular dysfunction associated with inadequate food intake.

Locus Coeruleus Dysfunction in Transgenic Rats with Low Brain Angiotensinogen

AIMS

Transgenic TGR(ASrAOGEN)680 (TGR) rats with specific downregulation of glial angiotensinogen (AOGEN) synthesis develop cardiovascular deficits, anxiety, altered response to stress, and depression. Here, we evaluated whether these deficits are associated with alteration of the integrity of the noradrenergic system originating from locus coeruleus (LC) neurons.

METHODS

Adult TGR rats were compared to control Sprague Dawley rats in terms of the following: tissue levels of transcripts encoding noradrenergic markers, tissue tyrosine hydroxylase (TH) protein level, in vivo TH activity, density of TH-containing fibers, behavioral response to novelty, locomotor activity, and polysomnography.

RESULTS

TH expression was increased in the LC of TGR rats compared to controls. In LC terminal fields, there was an increase in density of TH-containing fibers in TGR rats that was associated with an elevation of in vivo TH activity. TGR rats also displayed locomotor hyperactivity in response to novelty. Moreover, polysomnographic studies indicated that daily paradoxical sleep duration was increased in TGR rats and that the paradoxical sleep rebound triggered by total sleep deprivation was blunted in these rats.

CONCLUSIONS

Altogether, these results suggest that disruption of astroglial AOGEN synthesis leads to cardiovascular, cognitive, behavioral, and sleep disorders that might be partly due to LC dysfunction.

Role of neurons and glia in the CNS actions of the renin-angiotensin system in cardiovascular control

Despite tremendous research efforts, hypertension remains an epidemic health concern, leading often to the development of cardiovascular disease. It is well established that in many instances, the brain plays an important role in the onset and progression of hypertension via activation of the sympathetic nervous system. Further, the activity of the renin-angiotensin system (RAS) and of glial cell-mediated proinflammatory processes have independently been linked to this neural control and are, as a consequence, both attractive targets for the development of antihypertensive therapeutics. Although it is clear that the predominant effector peptide of the RAS, ANG II, activates its type-1 receptor on neurons to mediate some of its hypertensive actions, additional nuances of this brain RAS control of blood pressure are constantly being uncovered. One of these complexities is that the RAS is now thought to impact cardiovascular control, in part, via facilitating a glial cell-dependent proinflammatory milieu within cardiovascular control centers. Another complexity is that the newly characterized antihypertensive limbs of the RAS are now recognized to, in many cases, antagonize the prohypertensive ANG II type 1 receptor (AT1R)-mediated effects. That being said, the mechanism by which the RAS, glia, and neurons interact to regulate blood pressure is an active area of ongoing research. Here, we review the current understanding of these interactions and present a hypothetical model of how these exchanges may ultimately regulate cardiovascular function.

The renin angiotensin system and the metabolic syndrome

The renin angiotensin system (RAS; most well-known for its critical roles in the regulation of cardiovascular function and hydromineral balance) has regained the spotlight for its potential roles in various aspects of the metabolic syndrome. It may serve as a causal link among obesity and several co-morbidities. Drugs that reduce the synthesis or action of angiotensin-II (A-II; the primary effector peptide of the RAS) have been used to treat hypertension for decades and, more recently, clinical trials have determined the utility of these pharmacological agents to prevent insulin resistance. Moreover, there is evidence that the RAS contributes to body weight regulation by acting in various tissues. This review summarizes what is known of the actions of the RAS in the brain and throughout the body to influence various metabolic disorders. Special emphasis is given to the role of the RAS in body weight regulation. The paper represents an invited review by a symposium, award winner or keynote speaker at the Society for the Study of Ingestive Behavior [SSIB] Annual Meeting in Portland, July 2009.

Ang II and Ang IV: unraveling the mechanism of action on synaptic plasticity, memory, and epilepsy

The central angiotensin system plays a crucial role in cardiovascular regulation. More recently, angiotensin peptides have been implicated in stress, anxiety, depression, cognition, and epilepsy. Angiotensin II (Ang II) exerts its actions through AT(1) and AT(2) receptors, while most actions of its metabolite Ang IV were believed to be independent of AT(1) or AT(2) receptor activation. A specific binding site with high affinity for Ang IV was discovered and denominated "AT(4) receptor". The beneficiary effects of AT(4) ligands in animal models for cognitive impairment and epileptic seizures initiated the search for their mechanism of action. This proved to be a challenging task, and after 20 years of research, the nature of the "AT(4) receptor" remains controversial. Insulin-regulated aminopeptidase (IRAP) was first identified as the high-affinity binding site for AT(4) ligands. Recently, the hepatocyte growth factor receptor c-MET was also proposed as a receptor for AT(4) ligands. The present review focuses on the effects of Ang II and Ang IV on synaptic transmission and plasticity, learning, memory, and epileptic seizure activity. Possible interactions of Ang IV with the classical AT(1) and AT(2) receptor subtypes are evaluated, and other potential mechanisms by which AT(4) ligands may exert their effects are discussed. Identification of these mechanisms may provide a valuable target in the development in novel drugs for the treatment of cognitive disorders and epilepsy.

Baroreflex control of heart rate and renal sympathetic nerve activity in rats with low brain angiotensinogen

The main objective of the present study was to evaluate baroreceptor control of heart rate (HR) and renal sympathetic nerve activity (RSNA) in transgenic rats (TG) with low angiotensinogen production in glial cells, TGR(ASrAogen)-680. In addition, the sympathetic and vagal autonomic tonus to the heart was investigated. As previously shown, TG rats presented a lower arterial pressure (AP) and HR. However, TG rats had decreased AP variability during the night (8.9+/-0.4 mmHg vs 9.8+/-0.3 mmHg, in SD) accompanied by an increase in HR variability (39+/-1 beats/min vs 35+/-1 beats/min, in SD) and augmented locomotor activity during the night (3.5+/-0.3 counts/min vs 2.5+/-0.2 counts/min, in SD). In addition, TG rats presented increased baroreflex sensitivity for the RSNA (slope of line that correlates decreases in RSNA and increases in AP=1.36+/-0.18 vs 0.77+/-0.1, in SD) and an increased sensitivity for both the baroreflex bradycardia (0.79+/-0.04 ms/mmHg vs 0.52+/-0.04 ms/mmHg, in SD) and tachycardia (1.46+/-0.1 ms/mmHg vs 0.93+/-0.01 ms/mmHg, in SD). Further, TG rats had increased vagal tonus (25+/-3 beats/min vs 11+/-4 beats/min in SD) without significant change in the sympathetic tonus to the heart. These results confirm and extend previous observations showing that glial angiotensinogen, the main source of brain RAS peptides, importantly modulates sympathetic tonus, at least to the renal nerve, and vagal tonus to the heart.

Enzymatic pathways of the brain renin-angiotensin system: unsolved problems and continuing challenges

The brain renin-angiotensin system continues to be enigmatic more than 40 years after the brain was first recognized to be a site of action of angiotensin II. This review focuses on the enzymatic pathways for the formation and degradation of the growing number of active angiotensins in the brain. A brief description and nomenclature of the peptidases involved in the processing of angiotensin peptides in the brain is given. Of primary interest is the array of enzymes that degrade radiolabeled angiotensins in receptor binding assays. This poses major challenges to studies of brain angiotensin receptors and it is debatable whether an accurate determination of brain angiotensin receptor binding kinetics has yet been made. The quandary facing the investigator of brain angiotensin receptors is the need to protect the radioligand from metabolic alteration while maintaining the characteristics of the receptors in situ. It is the tenet of this review that we have yet to fully understand the binding characteristics of brain angiotensin receptors and the extent of their distribution in the brain because of our inability to fully protect the angiotensins from metabolic alteration until equilibrium binding conditions can be attained.

Specific receptor for angiotensinogen on human renal cells

BACKGROUND

We recently demonstrated the existence of an angiotensinogen (AGT) receptor on placental cells. It has been established that there is a tissue-specific renin-angiotensin system (RAS) in the human kidney. This study focused on whether human renal proximal tubule epithelial cells possessed an AGT receptor.

METHODS

Human renal proximal tubule epithelial cells were cultured in plastic wells. Binding assays were carried out by adding iodinated angiotensinogen ((125)I-AGT) to each culture well, with or without unlabeled AGT. The cells were washed, lysed, and the radioactivity was measured.

RESULTS

Human renal proximal tubule epithelial cells bound (125)I-AGT in a time-dependent manner. This binding was competitively and specifically inhibited by unlabeled AGT. Bound (125)I-AGT was competitively displaced by AGT. Acid washing removed 30% at 8 h, indicating that 70% bound AGT had been internalized. Scatchard plot binding analysis showed that the identified AGT receptor possessed a single class of high-affinity binding sites (K(d)=1.73 nmol, B(max)=23.39 pmol/10(6) cells).

CONCLUSION

The results of this study provide evidence for the presence of an AGT receptor on human renal proximal tubule epithelial cells. Our finding suggests that the AGT receptor may be an integral component of the renal RAS.

Mammalian embryonic cerebrospinal fluid proteome has greater apolipoprotein and enzyme pattern complexity than the avian proteome

During early stages of embryo development, the brain cavity is filled with Embryonic Cerebro-Spinal Fluid, which has an essential role in the survival, proliferation and neurogenesis of the neuroectodermal stem cells. We identified and analyzed the proteome of Embryonic Cerebro-Spinal Fluid from rat embryos (Rattus norvegicus), which includes proteins involved in the regulation of Central Nervous System development. The comparison between mammalian and avian Embryonic Cerebro-Spinal Fluid proteomes reveals great similarity, but also greater complexity in some protein groups. The pattern of apolipoproteins and enzymes in CSF is more complex in the mammals than in birds. This difference may underlie the greater neural complexity and synaptic plasticity found in mammals. Fourteen Embryonic Cerebro-Spinal Fluid gene products were previously identified in adult human Cerebro-Spinal Fluid proteome, and interestingly they are altered in patients with neurodegenerative diseases and/or neurological disorders. Understanding these molecules and the mechanisms they control during embryonic neurogenesis may contribute to our understanding of Central Nervous System development and evolution, and these human diseases.

Interleukin-1β enhances the angiotensin-induced expression of plasminogen activator inhibitor-1 through angiotensin receptor upregulation in human astrocytes

Plasminogen activator inhibitor-1 (PAI-1) regulates not only fibrinolysis but extracellular matrix remodeling, and angiotensin II is known to play an important role in controlling the expression of PAI-1 in astrocytes. We have studied the effect of interleukin-1beta (IL-1beta), one of major cytokines also active in the nervous system, on the angiotensin II-induced expression of PAI-1 in human astrocytes. Cultures of normal human astrocytes were stimulated with IL-1beta and angiotensin II, and the expression of mRNAs for angiotensin II type 1 receptor (AT1) and PAI-1 was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) or real-time quantitative PCR. PAI-1 protein in astrocyte-conditioned medium was measured by enzyme-linked immunosorbent assay (ELISA). IL-1beta enhanced the expression of AT1 in astrocytes in time- and concentration-dependent manners. After 24-h stimulation, 10 ng/ml IL-1beta and 10 nM angiotensin II increased the levels of PAI-1 protein in astrocyte-conditioned medium by 1.9-fold and 1.8-fold of the basal value, respectively. There was no synergistic effect when the cells were stimulated simultaneously with IL-1beta and angiotensin II. When the cells were stimulated, with angiotensin II, 16 h after the stimulation with IL-1beta, the production of PAI-1 was enhanced by 1.4-fold as compared to the cells stimulated only with IL-1beta. CV-11794, an AT1 antagonist, inhibited the enhanced PAI-1 production in response to angiotensin II. We conclude that IL-1beta increases angiotensin II-induced PAI-1 secretion by astrocytes through the induction of AT1, and the enhanced secretion of PAI-1 may modulate functions of plasminogen activators in the nervous system.

Glial-specific ablation of angiotensinogen lowers arterial pressure in renin and angiotensinogen transgenic mice

Angiotensinogen (AGT) is mainly expressed in glial cells in close proximity to renin-expressing neurons in the brain. We previously reported that glial-specific overexpression of ANG II results in mild hypertension. Here, we tested the hypothesis that glial-derived AGT plays an important role in blood pressure regulation in hypertensive mice carrying human renin (hREN) and human AGT transgenes under the control of their own endogenous promoters. To perform a glial-specific deletion of AGT, we used an AGT transgene containing loxP sites (hAGT(flox)), so the gene can be permanently ablated in the presence of cre-recombinase expression, driven by the glial fibrillary acidic protein (GFAP) promoter. Triple transgenic mice (RAC) containing a: 1) systemically expressed hREN transgene, 2) systemically expressed hAGT(flox) transgene, and 3) GFAP-cre-recombinase were generated and compared with double transgenic mice (RA) lacking cre-recombinase. Liver and kidney hAGT mRNA levels were unaltered in RAC and RA mice, as was the level of hAGT in the systemic circulation, consistent with the absence of cre-recombinase expression in those tissues. Whereas hAGT mRNA was present in the brain of RA mice (lacking cre-recombinase), it was absent from the brain of RAC mice expressing cre-recombinase, confirming brain-specific elimination of AGT. Immunohistochemistry revealed a loss of AGT immunostaining glial cells throughout the brain in RAC mice. Arterial pressure measured by radiotelemetry was significantly lower in RAC than RA mice and unchanged from nontransgenic control mice. These data suggest that there is a major contribution of glial-AGT to the hypertensive state in mice carrying systemically expressed hREN and hAGT genes and confirm the importance of a glial source of ANG II substrate in the brain.

Presynaptic Angiotensin II AT1 Receptors Enhance Inhibitory and Excitatory Synaptic Neurotransmission to Motoneurons and Other Ventral Horn Neurons in Neonatal Rat Spinal Cord

In neonatal spinal cord, we previously reported that exogenous angiotensin II (ANG II) acts at postsynaptic AT1 receptors to depolarize neonatal rat spinal ventral horn neurons in vitro. This study evaluated an associated increase in synaptic activity. Patch clamp recordings revealed that 38/81 thoracolumbar (T7–L5) motoneurons responded to bath applied ANG II (0.3–1 μM; 30 s) with a prolonged (5–10 min) and reversible increase in spontaneous postsynaptic activity, selectively blockable with Losartan ( n = 5) but not PD123319 ( n = 5). ANG-II-induced events included both spontaneous inhibitory (IPSCs; n = 6) and excitatory postsynaptic currents (EPSCs; n = 5). While most ANG induced events were tetrodotoxin-sensitive, ANG induced a significant tetrodotoxin-resistant increase in frequency but not amplitude of miniature IPSCs ( n = 7/13 cells) and EPSCs ( n = 2/7 cells). In 35/77 unidentified neurons, ANG II also induced a tetrodotoxin-sensitive and prolonged increase in their spontaneous synaptic activity that featured both IPSCs ( n = 5) and EPSCs ( n = 4) when tested in the presence of selective amino acid receptor antagonists. When tested in the presence of tetrodotoxin, ANG II was noted to induce a significant increase in the frequency but not the amplitude of mIPSCs ( n = 9) and mEPSCs ( n = 8). ANG also increased spontaneous motor activity from isolated mouse lumbar ventral rootlets. Collectively, these observations support the existence of a wide pre- and postsynaptic distribution of ANG II AT1 receptors in neonatal ventral spinal cord that are capable of influencing both inhibitory and excitatory neurotransmission.

Nuclear localization of angiotensinogen in astrocytes

In the brain, angiotensinogen (AGT) is primarily expressed in astrocytes; brain ANG II derived from locally produced AGT has been shown to influence blood pressure. To better understand the molecular basis of AGT expression in the brain, we identified a human astrocytoma cell line, CCF-STTG1, that expresses endogenous AGT mRNA and produces AGT protein. Studies examining CCF-STTG1 cell AGT after N- and O-glycosidase suggest that AGT may not be posttranslationally modified by glycosylation in these cells as it is in plasma. Small amounts of AGT (5% of HepG2) were detected in the culture medium, suggesting a low rate of AGT secretion. Immunocytochemical examination of AGT in CCF-STTG1 cells revealed mainly nuclear localization. Although this has not been previously reported, it is consistent with nuclear localization of other serpin family members. To examine this further, we generated a fusion protein consisting of green fluorescent protein (GFP) and human AGT and examined subcellular localization by confocal microscopy after confirming expression of the fusion protein by Western blot. In CCF-STTG1 cells, a control GFP construct lacking AGT was mainly localized in the cytoplasm, whereas the GFP-AGT fusion protein was primarily localized in the nucleus. To map the location of a potential nuclear localization signal, overlapping 500-bp fragments of human AGT cDNA were fused in frame downstream of GFP. Although four of the fusion proteins exhibited either perinuclear or cytoplasmic localization, one fusion protein encoding the COOH terminus of AGT was localized in the nucleus. Importantly, nuclear localization of human AGT was confirmed in primary cultures of glial cells isolated from transgenic mice expressing the human AGT under the control of its own endogenous promoter. Our results suggest that AGT may have a novel intracellular role in the brain apart from its predicted endocrine function.

Genetic targeting of the brain renin-angiotensin system in transgenic rats: Impact on stress-induced renin release

The advance of genetic technologies to permit tissue-specific targeted gene manipulation allowed the development of transgenic models with alterations of the renin-angiotensin (RAS) solely in the brain. We have used such methodology to develop a transgenic rat with a brain specific alteration of the RAS [TGR(ASrAOGEN)], in order to elucidate a causative role for the brain RAS and its relevance in different pathophysiological processes. The TGR(ASrAOGEN) rats have decreased levels of angiotensinogen (AOGEN) throughout the brain because of an antisense inhibition of the astroglial AOGEN synthesis. In this review we aimed at summarizing the experience obtained from utilizing the TGR(ASrAOGEN) rat model to study the brain RAS and present novel results providing evidence for the involvement of this system in stress-induced renin release.

Localization of components of the renin-angiotensin system in the suprachiasmatic nucleus of normotensive Sprague-Dawley rats: part A. angiotensin I/II, a light and electron microscopic study

The central pacemaker of the mammalian circadian clock, identified in the suprachiasmatic nucleus (SCN), is of special interest for many chronomedical studies on neuropeptides. Based on its role in the modulation of blood pressure and vasopressin release, the distribution and function of the neuropeptide angiotensin II (ANG II) in the SCN became a target for several immunohistological studies. At the light microscopic level, the distribution of ANG II in the SCN is well known, but detailed information about the localization of ANG II in the SCN at the ultrastructural level is missing. To gain further insight in the functional aspects of ANG II in the SCN, we investigated on the subcellular localization of the neuropeptide ANG II and its precursor ANG I in the SCN. The current report presents a light and electron microscopic study on ANG I/II-immunoreactivity in the suprachiasmatic nucleus of normotensive Sprague-Dawley rats.

Neuroendocrine control of body fluid metabolism

Mammals control the volume and osmolality of their body fluids from stimuli that arise from both the intracellular and extracellular fluid compartments. These stimuli are sensed by two kinds of receptors: osmoreceptor-Na+ receptors and volume or pressure receptors. This information is conveyed to specific areas of the central nervous system responsible for an integrated response, which depends on the integrity of the anteroventral region of the third ventricle, e.g., organum vasculosum of the lamina terminalis, median preoptic nucleus, and subfornical organ. The hypothalamo-neurohypophysial system plays a fundamental role in the maintenance of body fluid homeostasis by secreting vasopressin and oxytocin in response to osmotic and nonosmotic stimuli. Since the discovery of the atrial natriuretic peptide (ANP), a large number of publications have demonstrated that this peptide provides a potent defense mechanism against volume overload in mammals, including humans. ANP is mostly localized in the heart, but ANP and its receptor are also found in hypothalamic and brain stem areas involved in body fluid volume and blood pressure regulation. Blood volume expansion acts not only directly on the heart, by stretch of atrial myocytes to increase the release of ANP, but also on the brain ANPergic neurons through afferent inputs from baroreceptors. Angiotensin II also plays an important role in the regulation of body fluids, being a potent inducer of thirst and, in general, antagonizes the actions of ANP. This review emphasizes the role played by brain ANP and its interaction with neurohypophysial hormones in the control of body fluid homeostasis.

Localization of renin expressing cells in the brain, by use of a REN-eGFP transgenic model

Immunoreactive renin has been reported in the hypothalamus and cerebellar cortex in the rodent brain and in neurons in all areas of the human brain. Despite these observations and the clear documentation of the expression of the other renin-angiotensin system genes in the brain, the notion that renin is endogenously expressed in the brain remains very controversial and undefined. This controversy no doubt arises because the level of renin expression in the brain is below the detection threshold of most standard assays. A transgenic mouse expressing enhanced green fluorescence protein (eGFP) under the control of the mouse renin promoter was recently reported. This model expresses eGFP in the kidney, which responds appropriately to both developmental and physiological stimuli. We therefore used eGFP as a sensitive marker to identify renin-expressing cells in the brain. We identified eGFP-containing cells in specific areas of the brain, including cerebellum, hippocampus, dorsal motor nucleus of the vagus, inferior olivary nucleus, reticular formation, rostral ventrolateral medulla, central nucleus of the amygdala, lateral parabrachial nucleus, mesencephalic trigeminal nucleus, bed nucleus of stria terminalis, and subfornical organ. By colabeling with neuron- or glia (astrocytes or oligodendrocytes)-specific antisera, we have determined the eGFP-positive cells to be mainly neuronal. These findings therefore strongly support the primary expression of renin mRNA in the brain in regions controlling cardiovascular function.

Delayed maturation of catecholamine phenotype in nucleus tractus solitarius of rats with glial angiotensinogen depletion

Cerebral catecholamines and angiotensins are both involved in the regulation of cardiovascular function. Recent in vitro studies have suggested that angiotensin II modulates noradrenergic neurotransmission by controlling both the expression and neuritic trafficking of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. To assess the potential existence of such mechanisms in vivo, we compared TH phenotype ontogeny in the nucleus tractus solitarius (NTS), which is the first central relay of the baroreflex, between control Sprague-Dawley rats and TGR(ASrAOGEN) rats (TG) with glial specific angiotensinogen (AOGEN) depletion. TG displayed a delayed increase in both TH-mRNA and TH protein levels, which sharply rises in the NTS of control rats within the fourth week. The delayed maturation of TH phenotype also affected the presence of TH protein in the neuropil, not only within the NTS region but also within the ventrolateral medulla. This was evidenced by a large decrease in the density of TH-containing neuronal processes in TG at 4 weeks only, without noticeable modification of the labeling of the neuritic marker MAP2, suggesting that neuritic trafficking of TH protein was transiently altered. These results indicate that glial AOGEN is crucial to coordinate within the fourth week the mechanisms driving the maturation of NTS catecholaminergic neurons and suggest that impairment of the central angiotensinergic system early in development can lead to cardiovascular dysfunction related to altered maturation of catecholaminergic neurons located in both the dorsal and the ventrolateral medulla.

Angiotensin type 1 receptor immunoreactivity in the thoracic spinal cord

The angiotensin II type 1 receptor (AT1R) in the central nervous system (CNS) plays a pivotal role in determining blood pressure. However, the relationship of the receptor to neurones in the spinal cord which are the final CNS contribution to sympathetic outflow is unknown. Here we first use RT-PCR to show that AT1A, AT1B and AT2 receptors are expressed in thoracic spinal cord of the rat. Using light microscopic immunohistochemistry we find that the AT1 receptor in the thoracic spinal cord is located on neurones and ependymal cells. Neurones with extensive immunostaining of somata and dendrites were located in the intermediolateral cell column (IML) and lamina X (the central autonomic area), regions associated with autonomic outflow, as well as in lamina V. Retrograde labelling and dual immunolabelling with nNOS revealed that those AT1R-immunopositive cells in the IML were sympathetic preganglionic neurones, while those in lamina X were unlikely to be. Punctate labelling resembling that of axonal fibres and terminals was evident in lamina II of the dorsal horn and throughout the cord. Electron microscopy in the IML and lamina X revealed that these puncta were presynaptic terminals, but also astrocyte processes. Immunolabelling was also evident beneath the plasma membrane in neuronal somata. These data show that the AT1R in the spinal cord is ideally located to influence autonomic outflow and hence participate in the CNS determination of blood pressure.

Presence of cellular renin-angiotensin system in chromaffin cells of bovine adrenal medulla

The presence of a local renin-angiotensin system has been established in organs that serve as angiotensin targets. In this study, the expression of angiotensinogen mRNA and subcellular localization of renin, angiotensin-converting enzyme, and angiotensin II were investigated in bovine adrenal medullary cells in primary culture. By light microscopy, expression of angiotensinogen mRNA, immunoreactive renin, angiotensin-converting enzyme, and angiotensin II were readily detectable only in the chromaffin cells. The density distribution of renin and angiotensin II in sucrose gradients suggested a concentration in chromaffin granules, a localization directly confirmed by immunoelectron microscopy. Reverse transcriptase-polymerase chain reaction and sequencing confirmed the expression of angiotensinogen in bovine chromaffin cells and the adrenal medulla. In addition, in vitro autoradiography indicated that both angiotensin-converting enzyme and angiotensin type 1 receptors were present in the adrenal medulla. These results provide the first direct evidence that chromaffin cells in the adrenal medulla are not only the target for angiotensin but should also be considered as potential local angiotensin-generating and -storing cells.

Pigment epithelium-derived factor is elevated in CSF of patients with amyotrophic lateral sclerosis

Pigment epithelium-derived factor (PEDF), a recently defined retinal trophic factor and anti-angiogenic factor for the eye, is also present in the CNS and is a motor neuron protectant. We asked whether PEDF levels in CSF are altered in patients with amyotrophic lateral sclerosis (ALS). Pigment epithelium-derived factor protein was detected by quantitative western blot analysis with a PEDF-specific antiserum. Levels of PEDF in CSF, expressed as a ratio to total CSF protein, were significantly elevated 3.4-fold in 15 patients with ALS compared with neurologic disease controls (p < 0.0003). This increase does not seem likely to reflect up-regulation of PEDF synthesis in muscle in response to denervation, as CSF PEDF was not elevated in severe denervating diseases other than ALS. Nor does the increase represent some non-specific release in neurodegeneration, as CSF PEDF was not elevated in other neurodegenerative diseases. While the mechanism of this presumably reactive increase is not known, the distinctive, surprisingly elevated level of PEDF in the CSF may be an autoprotective reaction in ALS.

Enhancement of angiotensinogen expression in angiotensin II-dependent hypertension

Chronic infusion of angiotensin (Ang) II leads to the development of hypertension and enhances intrarenal Ang II content to levels greater than can be explained from the circulating concentrations of the peptide. We previously reported that renal angiotensinogen (Ao) mRNA is enhanced in Ang II-dependent hypertension and may contribute to augmented intrarenal Ang II levels, but the Ao protein levels were not significantly increased. Because a high-salt diet (H/S) has been shown to suppress renal expression of Ao mRNA, we examined the effects of chronic Ang II infusion on kidney and liver Ao mRNA and protein levels in male Sprague-Dawley rats (n=12) maintained on an 8% salt diet. Ang II was administered via osmotic minipumps (40 ng/min) to 1 group (n=6) while the remaining rats were sham-operated. A H/S diet alone did not alter systolic blood pressure in sham animals (109+/-6 mm Hg at day 12); however, Ang II infusions to the H/S rats significantly increased systolic blood pressure (167+/-7 at day 12) and intrarenal Ang II content (459+/-107 fmol/g versus 270+/-42) despite a marked suppression of plasma renin activity (0.9+/-0.2 ng Ang I. mL(-1). h(-1) versus 2.8+/-1.3). Ang II infusions significantly increased kidney Ao mRNA compared with the H/S diet alone by 1.9+/-0.1-fold. Western blot analysis of kidney protein extracts showed that the Ang II-infused rats had increased kidney Ao protein levels compared with the H/S diet alone (1.9+/-0.1-fold). Liver Ao mRNA and protein and plasma Ao protein were also significantly increased by Ang II infusions. These data demonstrate the effects of Ang II infusion to stimulate Ao mRNA and protein. Thus, the augmented intrarenal Ang II in Ang II-dependent hypertension may result, in part, by a positive amplification mechanism to activate renal expression of AO:

Expression of angiotensinogen mRNA and protein in angiotensin II-dependent hypertension

Chronic elevations in circulating angiotensin II (AngII) levels produce sustained hypertension and increased intrarenal AngII contents through multiple mechanisms, which may include sustained or increased local production of AngII. This study was designed to test the hypothesis that chronic AngII infusion increases renal angiotensinogen mRNA and protein levels, thus contributing to the increase in intrarenal AngII levels. AngII (80 ng/min) was infused subcutaneously for 13 d into Sprague-Dawley rats, using osmotic minipumps. Control rats underwent sham operations. By day 12, systolic arterial BP increased to 184 +/- 3 mmHg in AngII-treated rats, whereas values for sham-treated rats remained at control levels (125 +/- 1 mmHg). Plasma renin activity was markedly suppressed (0.2 +/- 0.1 versus 5.3 +/- 1.2 ng AngI/ml per h); however, renal AngII contents were significantly increased in AngII-treated rats (273 +/- 29 versus 99 +/- 18 fmol/g). Western blot analyses of plasma and liver protein using a polyclonal anti-angiotensinogen antibody demonstrated two specific immunoreactive bands, at 52 and 64 kD, whereas kidney tissue exhibited one band, at 52 kD. Densitometric analyses demonstrated that AngII infusion did not alter plasma (52- or 64-kD), renal (52-kD), or hepatic (52-kD) angiotensinogen protein levels; however, there was a significant increase in hepatic expression of the highly glycosylated 64-kD angiotensinogen protein, of almost fourfold (densitometric value/control value ratios of 3.79 +/- 1.16 versus 1.00 +/- 0.35). Renal and hepatic expression of angiotensinogen mRNA, which was examined by semiquantitative reverse transcription-PCR, was significantly increased in AngII-treated rats, compared with shamtreated rats (kidney, densitometric value/glyceraldehyde-3-phosphate dehydrogenase mRNA value ratios of 0.82 +/- 0.11 versus 0.58 +/- 0.04; liver, densitometric value/glyceraldehyde-3-phosphate dehydrogenase mRNA value ratios of 2.34 +/- 0.07 versus 1.32 +/- 0.15). These results indicate that increases in circulating AngII levels increase intrarenal angiotensinogen mRNA levels, which may contribute to the sustained renal AngII-generating capacity that paradoxically occurs in AngII-treated hypertensive rats.

Hormonal and neurotransmitter roles for angiotensin in the regulation of central autonomic function

In this review we present the case for both hormonal and neurotransmitter actions of angiotensin II (ANG) in the control of neuronal excitability in a simple neural pathway involved in central autonomic regulation. We will present both single-cell and whole-animal data highlighting hormonal roles for ANG in controlling the excitability of subfornical organ (SFO) neurons. More controversially we will also present the case for a neurotransmitter role for ANG in SFO neurons in controlling the excitability of identified neurons in the paraventricular nucleus (PVN) of the hypothalamus. In this review we highlight the similarities between the actions of ANG on these two populations of neurons in an attempt to emphasize that whether we call such actions "hormonal" or "neurotransmitter" is largely semantic. In fact such definitions only refer to the method of delivery of the chemical messenger, in this case ANG, to its cellular site of action, in this case the AT1 receptor. We also described in this review some novel concepts that may underlie synthesis, metabolic processing, and co-transmitter actions of ANG in this pathway. We hope that such suggestions may lead ultimately to the development of broader guiding principles to enhance our understanding of the multiplicity of physiological uses for single chemical messengers.

Glial angiotensinogen regulates brain angiotensin II receptors in transgenic rats TGR(ASrAOGEN)

TGR(ASrAOGEN)680, a newly developed transgenic rat line with specific downregulation of astroglial synthesis of angiotensinogen, exhibits decreased brain angiotensinogen content associated with a mild diabetes insipidus and lower blood pressure. Autoradiographic experiments were performed on TGR(ASrAOGEN) (TG) and Sprague-Dawley (SD) control rats to quantify AT(1) and AT(2) receptor-binding sites in different brain nuclei and circumventricular organs. Dose-response curves for drinking response to intracerebroventricular injections of ANG II were compared between SD and TG rats. In most of the regions inside the blood-brain barrier [paraventricular nucleus (PVN), piriform cortex, lateral olfactory tract (LOT), and lateral preoptic area (LPO)], AT(1) receptor binding (sensitive to CV-11974) was significantly higher in TG compared with SD. In contrast, in the circumventricular organs investigated [subfornical organ (SFO) and area postrema], AT(1) receptor binding was significantly lower in TG. AT(2) receptors (binding sensitive to PD-123319) were detected at similar levels in the inferior olive (IO) of both strains. Angiotensin-binding sites sensitive to both CV-11974 and PD-123319 were detected in the LPO of SD rats and specifically upregulated in LOT, IO, and most notably PVN and SFO of TG. The dose-response curve for water intake after intracerebroventricular injections showed a higher sensitivity to ANG II of TG (EC(50) = 3.1 ng) compared with SD (EC(50) = 11.2 ng), strongly suggesting that the upregulation of AT(1) receptors inside the blood-brain barrier of TG rats is functional. Finally, we showed that downregulation of angiotensinogen synthesized by astroglial cells differentially regulates angiotensin receptor subtypes inside the brain and in circumventricular organs.

Secretion of renin-angiotensin system (RAS) components by normal and tumoral lactotropes. A comparative study using reverse hemolytic plaque assay (RHPA) and immunoelectron microscopy

Immunodetection of renin-angiotensin system (RAS) components indicates that there is a local RAS in anterior pituitary cells, particularly in lactotropes. We have attempted to determine if RAS molecules are secreted by lactotropes and the secretory pathways and intracellular sites of maturation. We investigated the secretory activity of individual lactotropes, using the reverse hemolytic plaque assay (RHPA), with GH3B6 tumor cells and normal male rat pituitary cells. We also determined the subcellular distributions of RAS components in these cells. Both tumor and normal cells secreted angiotensinogen, prorenin, renin, angiotensin I, angiotensin-converting enzyme, and angiotensin II, although at different levels. The percentage of secretory cells was generally higher in tumor lactotropes than in normal cells. The subcellular distribution of RAS components obtained by immunoperoxidase was very similar in both cell types, although the intensities of immunoreactivity differed. Cleaved and uncleaved components were found in rough endoplasmic reticulum (RER), Golgi saccules, and secretory granules, all compartments of the secretory pathway. The cleaved components in the RER suggest the existence of early maturation, whereas the presence of uncleaved products in the secretory granules of normal lactotropes might indicate late maturation sites.

Angiotensinogen and angiotensin converting enzyme gene polymorphisms and the risk of bipolar affective disorder in humans

A possible participation of the renin-angiotensin system (RAS) components with mood disturbances has been suggested in both animal and pharmacological models. In this cross-sectional study, we examined the association between functional polymorphisms in the angiotensin converting enzyme (ACE) and angiotensinogen (AGT) genes in 115 bipolar affective disorder (BPAD) patients and 323healthy control subjects. The ACE I/D variant did not show any difference in allelic frequencies and genotypic distribution between the groups. In contrast, when studying the AGT M235T polymorphism we found that the M allele was more frequently observed in BPAD patients than in controls (chi(2)=6.766, d.f.=1, P=0.009). Using multivariate logistic models the strongest odds ratio resulted from a dominant genetic model (OR=3.0; CI (95%) 1.7-5.3] Our data suggest an association between the AGT M235 genotype and increased susceptibility for BPAD in these Brazilian patients. These findings are consistent with the hypothesis that the RAS system plays a role in regulating the mood

Characterization of apelin, the ligand for the APJ receptor

The apelin peptide was recently discovered and demonstrated to be the endogenous ligand for the G protein-coupled receptor, APJ. A search of the GenBank databases retrieved a rat expressed sequence tag partially encoding the preproapelin sequence. The GenBank search also revealed a human sequence on chromosome Xq25-26.1, containing the gene encoding preproapelin. We have used the rat sequence to screen a rat brain cDNA library to obtain a cDNA encoding the full-length open reading frame of rat preproapelin. This cDNA encoded a protein of 77 amino acids, sharing an identity of 82% with human preproapelin. Northern and in situ hybridization analyses revealed both human and rat apelin and APJ to be expressed in the brain and periphery. Both sequence and mRNA expression distribution analyses revealed similarities between apelin and angiotensin II, suggesting they that share related physiological roles. A synthetic apelin peptide was injected intravenously into male Wistar rats, resulting in immediate lowering of both systolic and diastolic blood pressure, which persisted for several minutes. Intraperitoneal apelin injections induced an increase in drinking behavior within the first 30 min after injection, with a return to baseline within 1 h.

Transcriptional regulation of angiotensinogen gene expression

The renin--angiotensin system (RAS) is an extracellular hormonal system implicated in acute, homeostatic control of peripheral vascular resistance and electrolyte homeostasis. In this tightly regulated system, physiological regulators of blood pressure and fluid balance induce the production of the potent vasoactive angiotensin peptides by sequential proteolysis of the angiotensinogen (AGT) prohormone. AGT is the only known precursor of the angiotensin peptides, whose circulating concentrations influence the tonic activity of the RAS. AGT abundance is regulated at the transcriptional level through hormonal and cell-type specific regulators. In this review, we will discuss the identified mechanisms controlling AGT expression separately for the rodent and human genes. The most intensively investigated gene (rodent AGT) is regulated constitutively by multiple positive- and negative-acting cis factors that function in a cell-type dependent fashion. Inducible rodent AGT expression is mediated through a multihormone-inducible enhancer that integrates signals from steroid and cytokine hormones into AGT transcription. We review recent advances in understanding the mechanism of the nuclear factor-kappa B (NF-kappa B) family in mediating cytokine-induced AGT expression and our recent discoveries on the existence of differentially inducible pools of cytoplasmic NF-kappa B. Constitutive control of the human AGT gene will be discussed; there is surprisingly little information on the cis- and trans-acting regulators controlling inducible expression of human AGT. Finally, we will explore some of the recent developments in gene linkage studies where human AGT alleles have been associated with hypertensive phenotypes through a mechanism that may involve enhanced transcription. These studies have provided a molecular explanation for a subset of heritable hypertensive disorders in humans.

The ontogeny of salt hunger in the rat

Salt hunger is the behaviour of an animal suffering sodium deficiency. It is characterised by an increased motivation to seek and ingest sodium, and the ability to distinguish between sodium and other salts. Here I review the development of salt hunger in the rat. Salt hunger develops rapidly between birth and weaning. It can first be demonstrated 72 h postnatally when an intracerebroventricular injection of renin elicits greater swallowing of NaCl solution than water and greater mouthing of solid fragments of NaCl than of an artificial sweetener. However, sodium deficit per se cannot arouse the hunger at this age, and first elicits increased intake of NaCl only at 12 days-of-age. The next landmark is at 17 days-of-age when the hormonal synergy of aldosterone and central angiotensin II first elicits salt hunger, as it does in the adult. The specificity of the hunger for the sodium ion also develops postnatally: the 72 h-old sodium-hungry neonate does not distinguish between NaCl and other mono- and di-valent chloride salts but, increasingly during development, the sodium hungry pup distinguishes salts and by weaning age NaCl is clearly preferred to other salts almost as it is in adults. Early development may also be a sensitive period for determining lifelong preferences, and indeed, acute perinatal sodium depletion induces a lifelong enhancement of salt intake. Taken together, these findings demonstrate how a behaviour develops precociously and how, when the behaviour becomes important at weaning, the rat pup is competent to meet its sodium requirements, and may be adapted to anticipate sodium deficit.

Angiotensin II-induced calcium signalling in neurons and astrocytes of rat circumventricular organs

The subfornical organ and organum vasculosum laminae terminalis represent neuroglial circumventricular organ structures bordering the anterior third cerebral ventricle. Owing to the absence of the blood-brain barrier, the cellular elements of the subfornical organ and the organum vasculosum laminae terminalis can be reached by circulating messenger molecules transferring afferent information. As demonstrated for the control of extracellular fluid composition, the circulating hormone angiotensin II acts on these sensory circumventricular organs to induce drinking, elevated peripheral resistance and neurohypophyseal hormone release via interaction with membrane-spanning receptor proteins. To characterize the cell-specific distribution of angiotensin II receptors within the circumventricular organs, primary cell cultures derived from the subfornical organ or organum vasculosum laminae terminalis of five- to six-day-old rat pups were used to measure alterations in intracellular calcium at the single cell level. Neurons and astrocytes were identified by immunocytochemical staining for specific marker proteins. Bath application of angiotensin II (10(-10)-10(-6) M) dose-dependently induced calcium transients in neurons (19.6%) and astrocytes (15.7%), and angiotensin II threshold concentrations to elicit intracellular calcium signalling proved to be one order of magnitude higher in astrocytes as compared to neurons (10(-9) M). At angiotensin II concentrations higher than 10(-7) M, pronounced desensitization of the angiotensin II receptor occurred. Employing the angiotensin II receptor antagonists losartan (DUP-753; AT1-receptor) and PD-123319 (AT2-receptor), exclusive expression of the AT1 receptor subtype coupled to intracellular calcium concentration signalling could be demonstrated for neurons and astrocytes. In all cells examined, the angiotensin II-evoked increase in intracellular calcium concentrations could be fully suppressed in the absence of extracellular calcium. Co-activation by angiotensin II and other agents (vasopressin, its fragment 8-arginine-vasopressin(4-9), oxytocin, endothelin) was indicated for subfornical organ neurons and organum vasculosum laminae terminalis astrocytes.

Angiotensinogen, prorenin, and renin are Co-localized in the secretory granules of all glandular cells of the rat anterior pituitary: an immunoultrastructural study

In addition to the circulating renin-angiotensin system (RAS), a local system has been postulated in the anterior pituitary because immunodetection of its components in various mammalian species. However, different cell types appear to be involved in different species, and there is no general consensus on the subcellular localization of prorenin, renin and angiotensinogen. In this ultrastructural study, we investigated and quantified the presence of these components using double or triple immunogold labeling methods, in all the immunologically identified glandular cell types of the rat anterior pituitary. In contrast to previous reports, all these components were identified not only in lactotropes and gonadotropes but also in somatotropes, corticotropes, and thyrotropes. The highest levels were detected in lactotropes and gonadotropes, and renin gave the greatest signal. Angiotensinogen, prorenin, and renin were co-localized in the secretory granules of all rat pituitary glandular cell types. The simultaneous detection of the substrate (angiotensinogen) and both its specific cleavage enzyme and its proenzyme within the same granule suggests intragranular processing of this component. Moreover, the localization of these three constituents in the secretory granules also suggests that, in the rat anterior pituitary, they follow the regulated secretory pathway.

Ontogenic expression of natriuretic peptide mRNAs in postnatal rat brain: implications for development?

The central natriuretic peptide system is composed of at least three structurally homologous and uniquely distributed peptides and receptors which are thought to be involved in the central regulation of cardiovascular and autonomic function and more recently been shown to affect cellular growth and proliferation, processes pertinent to mammalian development. As such, following our initial mapping of preproatrial natriuretic peptide (ppANP) mRNA in adult brain [M.C. Ryan, A.L. Gundlach, Anatomical localization of preproatrial natriuretic peptide mRNA in the rat brain by in situ hybridization histochemistry: in olfactory regions, J. Comp. Neurol., 356 (1995) 168-182], it was of interest to determine the ontogenic expression of natriuretic peptide mRNAs in the developing rat brain. Using in situ hybridization histochemistry of specific [35S]- or [33P]-labeled oligonucleotides, ppANP and preproC-type natriuretic peptide (ppCNP) mRNAs were detected in the developing rat brain from postnatal day 4 to day 60 (adult). PpANP mRNA was observed in many hindbrain, but only some forebrain, regions at postnatal day 4. Regional differences in the temporal expression of ppANP mRNA were apparent with ppANP mRNA detected in the medial preoptic area, mammillary nuclei and medial habenular nucleus at postnatal day 4 and in other areas including the arcuate and dorsomedial hypothalamic nuclei and in olfactory and limbic regions at postnatal day 10. A number of regions also exhibited transient expression of ppANP mRNA such as the bed nucleus of the stria terminalis and the medial cerebellar nucleus. In contrast, ppCNP mRNA was detected at relatively high levels in several regions on postnatal day 4 including olfactory nuclei, the hippocampus and particularly the pontine nucleus. The level of expression appeared to increase markedly in most regions including forebrain olfactory and hippocampal areas and in brainstem regions including the pontine nucleus, the parvocellular and lateral reticular and spinal trigeminal nuclei by postnatal days 10 and 13, but decreased from this peak to equivalent to adult levels by postnatal day 28. The differential and transient expression of the natriuretic peptides during postnatal development, together with previous reports of the ontogenic regulation of natriuretic peptide receptor expression and binding patterns, further suggests their involvement in developmental processes in the rat CNS and provides information relevant to the likely functional development of natriuretic peptide-utilizing pathways.

Essential hypertension and 5' upstream core promoter region of human angiotensinogen gene

The angiotensinogen (AGT) gene M235T variant is associated with essential hypertension and elevated plasma AGT concentrations, although the underlying mechanisms are unknown. Recent studies have suggested that AGCE 1 (human AGT gene core promoter element 1) located in the 5' upstream core promoter region (position -25 to -1) of the human AGT gene has an important part in the expression of AGT mRNA by binding with transcription factor AGCF 1 (human AGT gene core promoter element binding factor 1), and a mutation at -20 from adenine to cytosine (A-20C) increases the level of expression of this transcript. We therefore examined subjects with this mutation to study the association with increased plasma AGT concentrations and with essential hypertension. One hundred eighty-eight subjects receiving no antihypertensive medication were examined with regard to the correlation between A-20C and plasma AGT concentrations, and 234 subjects were studied with respect to the association between A-20C and essential hypertension. A-20C was determined by polymerase chain reaction-restriction fragment length polymorphism analysis with EcoOR 109I. Multiple regression analysis showed a weak but significant correlation between A-20C and plasma AGT concentrations (P=.047) and essential hypertension (P=.049). The results suggest that A-20C may underlie the increase in plasma AGT concentrations and be involved in the development of essential hypertension.

Aminopeptidase A: distribution in rat brain nuclei and increased activity in spontaneously hypertensive rats

Aminopeptidase A is a membrane-bound zinc metalloprotease which cleaves angiotensin II into angiotensin III. Using a new specific aminopeptidase A inhibitor, EC33, we evaluated its enzymatic activity in several microdissected brain nuclei involved in the control of cardiovascular functions and in the pituitary. We compared this distribution with that of the angiotensin I-converting enzyme which converts angiotensin I to angiotensin II. Aminopeptidase A activity was heterogenously distributed with a 150-fold difference between the lowest and the highest levels. The pituitary and the circumventricular organs were the richest source of enzyme, followed by the median eminence, the arcuate nucleus, the area postrema, the choroid plexus and the supraotic and paraventricular nuclei. We did not find any close parallel between aminopeptidase A and angiotensin I-converting enzyme distributions. We examined both enzymatic activities in brain nuclei of spontaneously hypertensive rats. Aminopeptidase A activity was higher in the spontaneously hypertensive rats than in age-matched Wistar Kyoto control rats. The difference was up to 2.5-fold in several brain nuclei involved in the blood pressure regulation; in contrast, no differences in angiotensin I-converting enzyme activity were found in the same regions. The close correspondence between the distribution of aminopeptidase A activity and angiotensin receptors and nerve terminals in the brain associated with the observation that aminopeptidase A activity was overactivated in the spontaneously hypertensive rats suggest that this enzyme may contribute, at least in part, to the regulation of cardiovascular functions by its ability to convert angiotensin II to angiotensin III.

Novel perspectives on pituitary and brain angiotensinogen

All the angiotensin peptides originate from angiotensinogen, a glycoprotein synthesized by several tissues, including the brain and the anterior pituitary. In the rat, immunohistochemistry has been used to localize angiotensinogen in gonadotropes and in uncharacterized cells surrounding sinusoids. Both cell types are capable of secreting angiotensinogen in cell culture; only the gonadotropes contain angiotensin II (AngII) and are capable of secreting it in culture. It has been asserted that the perisinusoidal cells are the only source of angiotensinogen for the generation of AngII by gonadotropes. Our current data favor the existence of a complete intracellular renin-angiotensin system (RAS) in gonadotropes and a separate extracellular system which utilizes the high concentration of angiotensinogen from perisinusoidal cells. Furthermore, we postulate that gonadotrope AngII serves mainly reproductive functions, while the proximity of angiotensinogen-secreting cells to folliculostellate cells, and their access to the intercellular sinusoidal and follicular spaces, places the extracellular RAS in a strategic position to affect pituitary growth and the mediation of acute-phase immune responses. In the rat brain, angiotensinogen is expressed by the 16-18th day of fetal life and by areas generally concerned with vasopressor, electrolyte, and fluid homeostasis. Antisense deoxyoligonucleotides to angiotensinogen mRNA lower blood pressure in hypertensive rats and inhibit in vitro growth of neuroblastoma cells, indicating a significant role for angiotensinogen in mitogenic and homeostatic functions. It is commonly agreed that astrocytes express angiotensinogen. Neuronal angiotensinogen has also been demonstrated by immunohistochemistry, as a secretion from neuronal cell cultures, and by reverse-transcriptase polymerase chain reaction. The fate of secreted astrocytic and neuronal angiotensinogen remains obscure. Angiotensinogen is regulated in a tissue-specific manner with smaller or absent responses observed for brain tissue. By using astrocyte and neuronal cultures the actions on angiotensinogen production of growth hormone, IGF-1, inflammatory lipopolysaccharide, and phorbol ester have been examined. Recent observations show that angiotensinogen is regulated positively or negatively by glucocorticoids and that a positive synergism between cAMP and glucocorticoids exists. On the basis of analogous systems for other proteins, a scheme involving glucocorticoid receptors, CREB, and AP-1 transcription factors is formulated to explain glucocorticoid-cAMP interactions. These transcriptional interactions may form a significant functional link between the RAS and adrenergic mechanisms.