Developmental expression of the angiotensinogen gene in rat embryos

Subcellular characteristics of functional intracellular renin-angiotensin systems

The renin-angiotensin system (RAS) is now regarded as an integral component in not only the development of hypertension, but also in physiologic and pathophysiologic mechanisms in multiple tissues and chronic disease states. While many of the endocrine (circulating), paracrine (cell-to-different cell) and autacrine (cell-to-same cell) effects of the RAS are believed to be mediated through the canonical extracellular RAS, a complete, independent and differentially regulated intracellular RAS (iRAS) has also been proposed. Angiotensinogen, the enzymes renin and angiotensin-converting enzyme (ACE) and the angiotensin peptides can all be synthesized and retained intracellularly. Angiotensin receptors (types I and 2) are also abundant intracellularly mainly at the nuclear and mitochondrial levels. The aim of this review is to focus on the most recent information concerning the subcellular localization, distribution and functions of the iRAS and to discuss the potential consequences of activation of the subcellular RAS on different organ systems.

Development of fetal brain renin-angiotensin system and hypertension programmed in fetal origins

Since the concept of fetal origins of adult diseases was introduced in 1980s, the development of the renin-angiotensin system (RAS) in normal and abnormal patterns has attracted attention. Recent studies have shown the importance of the fetal RAS in both prenatal and postnatal development. This review focuses on the functional development of the fetal brain RAS, and ontogeny of local brain RAS components in utero. The central RAS plays an important role in the control of fetal cardiovascular responses, body fluid balance, and neuroendocrine regulation. Recent progress has been made in demonstrating that altered fetal RAS development as a consequence of environmental insults may impact on "programming" of hypertension later in life. Given that the central RAS is of equal importance to the peripheral RAS in cardiovascular regulation, studies on the fetal brain RAS development in normal and abnormal patterns could shed light on "programming" mechanisms of adult cardiovascular diseases in fetal origins.

ANG II-stimulated DNA synthesis is mediated by ANG II receptor-dependent Ca2+/PKC as well as EGF receptor-dependent PI3K/Akt/mTOR/p70S6K1 signal pathways in mouse embryonic stem cells

Effect of angiotensin II (ANG II) on mouse embryonic stem (ES) cell proliferation was examined. ANG II increased [(3)H] thymidine incorporation in a time- (>4 h) and dose- (>10(-9) M) dependent manner. The ANG II-induced increase in [(3)H] thymidine incorporation was blocked by inhibition of ANG II type 1 (AT(1)) receptor but not by ANG II type 2 (AT(2)) receptor, and AT(1) receptor was expressed. ANG II increased inositol phosphates formation and [Ca(2+)](i), and translocated PKC alpha, delta, and zeta to the membrane fraction. Consequently, the inhibition of PLC/PKC suppressed ANG II-induced increase in [(3)H] thymidine incorporation. The inhibition of EGF receptor kinase or tyrosine kinase prevented ANG II-induced increase in [(3)H] thymidine incorporation. ANG II phosphorylated EGF receptor and increased Akt, mTOR, and p70S6K1 phosphorylation blocked by AG 1478 (EGF receptor kinase blocker). ANG II-induced increase in [(3)H] thymidine incorporation was blocked by the inhibition of p44/42 MAPKs but not by p38 MAPK inhibition. Indeed, ANG II phosphorylated p44/42 MAPKs, which was prevented by the inhibition of the PKC and AT(1) receptor. ANG II increased c-fos, c-jun, and c-myc levels. ANG II also increased the protein levels of cyclin D1, cyclin E, cyclin-dependent kinase (CDK) 2, and CDK4 but decreased the p21(cip1/waf1) and p27(kip1), CDK inhibitory proteins. These proteins were blocked by the inhibition of AT(1) receptor, PLC/PKC, p44/42 MAPKs, EGF receptor, or tyrosine kinase. In conclusion, ANG II-stimulated DNA synthesis is mediated by ANG II receptor-dependent Ca(2+)/PKC and EGF receptor-dependent PI3K/Akt/mTOR/p70S6K1 signal pathways in mouse ES cells.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

ANG II increases 2-deoxyglucose uptake in mouse embryonic stem cells

It is now suggested that all components of the renin-angiotensin system are present in many tissues, including the embryo and may play a major role in embryo development and differentiation. However, little is known regarding whether ANG II regulates glucose transport in mouse embryonic stem (ES) cells. Thus, the effects of ANG II on [3H]-2-deoxyglucose (2-DG) uptake and its related signal pathways were examined in mouse ES cells. ANG II significantly increased cell proliferation and 2-DG uptake in concentration- and time-dependent manner (>18 h, >10(-8) M) and increased mRNA and protein level of GLUT1 by 31+/-7% and 22+/-5% compared to control, respectively. Actinomycin D and cycloheximide completely blocked the effect of ANG II on 2-DG uptake. ANG II-induced increase of 2-DG uptake was blocked by losartan, an ANG II type 1 (AT1) receptor blocker, but not by PD 123319, an ANG II type 2 (AT2) receptor blocker. In addition, ANG II-induced stimulation of 2-DG uptake was attenuated by phospholipase C (PLC) inhibitors, neomycin and U 73122 and ANG II increased inositol phosphates (IPs) formation by 37+/-8% of control. Protein kinase C (PKC) inhibitors, staurosporine, bisindolylmaleimide I, and H-7 also blocked ANG II-induced stimulation of 2-DG uptake. Indeed, ANG II activated a PKC translocation from the cytosolic to membrane fraction, suggesting a role of PKC. A 23187 (Ca2+ ionophore) increased 2-DG uptake and nifedifine (L-type Ca2+ channel blocker) blocked it. In conclusion, ANG II increased 2-DG uptake by PKC activation via AT1 receptor in mouse ES cells.

Multiple angiotensin receptor subtypes in normal and tumor astrocytes in vitro

A role for neuropeptide receptors in glial tumorigenesis has recently been proposed. Although angiotensin receptors are known to mediate proliferative effects in many cell types, including brain astrocytes, the possible participation of these receptors in glial tumorigenesis remains unknown. In the present study, we have examined the expression of the molecularly defined angiotensin receptor subtypes AT(1a), AT(1b), and AT(2) in normal perinatal rat astrocytes and in a panel of tumor adult astrocytoma cells, using the reverse transcriptase-polymerase chain reaction (RT-PCR). Subsequently, we compared the mitogenic effect of the angiotensins A(1-8), A(2-8), A(3-8) and the heptapeptide "metabolite" A(1-7), on both normal and tumor astrocytes, measured in terms of the incorporation of tritiated thymidine. Our results indicate that AT(1a), AT(1b), and AT(2) angiotensin receptor mRNA is commonly expressed by many of these cells. Of notable exception is the astrocytoma U373 which was not found to express AT(1) or AT(2) mRNA. Chronic (24-h) incubation of cells with A(1-8) and A(1-7) lead to the induction of mitogenesis, even in the AT(1) and AT(2) mRNA negative astrocytoma cell line U373. Moreover, pharmacological analysis indicated that the observed mitogenic effects are not mediated by the AT(1) or AT(2) type receptors, but rather by a novel, specific A((1-7)) angiotensin receptor, since mitogenesis was shown to be partially blocked by the A(1-7) analogue D-Ala(7)A(1-7) and by the protease inhibitor orthophenanthroline (100 microM). Using Fura-2 spectrophotometry, we found that activation of this receptor does not alter intracellular calcium levels; however, preincubation with the protein kinase kinase inhibitor U0126 (10 microM) was found to inhibit these mitogenic effects partially. Overall, these results which demonstrate that normal and tumor astrocytes express a greater variety of angiotensin receptor subtypes than previously thought, support the idea that A(1-7) and its receptor signaling system may play an important role in shaping the astrocyte population during development. Moreover, the untimely expression of this A((1-7)) receptor may represent an important etiological component in the development of brain astrocytomas.

Angiotensin II is a growth factor in the peri-implantation rat embryo

Angiotensin II (ANG II) is increasingly recognised as a growth factor, both in its own right and through interactions with other growth factors. There is a high density of ANG II receptors in the rat fetus, especially the AT2 receptor, the function of which is still uncertain. We have now studied the effects of ANG II on growth and development in the rat embryo in vitro between d 9.5 and 11.5, and characterised the receptor subtype mediating these effects. Embryos were cultured in whole rat serum, a high molecular weight retenate after ultrafiltration of whole rat serum, retenate with angiotensin II and retenate with ANG II and AT1 or AT2 receptor blockers. Growth and development were scored using conventional methods. Culture in retenate was associated with a marked reduction in growth and development by comparison with whole rat serum. This was partly, and significantly (P < 0.001), reversed by angiotensin II. The optimum concentration of angiotensin II was found to be angiotensin II 10(-11) M, within the physiological range. Angiotensin II had highly significant effects on both somatic (P < 0.001) and yolk sac/allantoic (P < 0.005) development. The latter effects suggest a role for angiotensin II in placentation. The effects of angiotensin II were blocked by PD123319, an AT2 blocker, but not by GR117289, an AT1 blocker. Interestingly, culture in retenate with GR117289 without added angiotensin II was also associated with some increase in growth (P < 0.05). Angiotensin II in low concentrations was measurable in the retenate, presumably arising from the action of endogenous renin on angiotensinogen. We therefore postulate that this effect of GR117289 was due to the action of endogenous angiotensin II on 'uncovered' AT2 receptors. This study has thus demonstrated a direct growth promoting effect of angiotensin II during organogenesis in the whole rat embryo in vitro. This effect is mediated through the AT2 receptors.

Development of functional zonation in the rat adrenal cortex

In an attempt to elucidate the mechanism(s) through which the functional adrenal cortex is established, we analyzed immunohistochemically the expression of various markers for the adrenocortical zones, i.e. the zona glomerulosa (zG), the zona fasciculata (zF), and the zona reticularis (zR), as well as markers for the medulla, and further examined the distribution and behavior of DNA-synthesizing cells in rat adrenal glands during development. The results showed that 1) separation of the cortex and medulla, and the development of functional zonation in the cortex began at around the time of birth, 2) at fetal stages when cortical zonation was not established, DNA-synthesizing cells were found scattered throughout the gland, where they proliferated without significant migration, and 3) after birth in the adrenal cortex with established cortical zonation, DNA-synthesizing cells were localized near the undifferentiated zone between zG and zF, and then they migrated centripetally. Cell death appeared to occur in the innermost portion of the cortex, where many resident macrophages are present. These findings illustrate basic processes underlying adrenal development and suggest that the undifferentiated region is apparently the stem cell zone of the adrenal cortex that maintains the cortical zonation.

Developmental expression of human angiotensinogen in transgenic mice

Transgenic mice containing the human angiotensinogen (HAGT) gene were utilized to determine the developmental regulation of HAGT expression. RNase protection assay on total RNA obtained from whole transgenic fetuses revealed that HAGT expression was first detected at embryonic day 8.5 (E8.5) and was abundant from E9.5 onward. The earliest expression of the HAGT transgene appeared to precede the earliest expression of the endogenous mouse AGT gene by 1-2 days. Northern blot analysis revealed moderate levels of HAGT mRNA in liver and kidney and low levels of HAGT mRNA in heart and brain from E16.5 (day 16.5 of gestation) onward. HAGT mRNA in liver, although abundant during late gestation and in 2-wk-old and adult mice, decreased transiently around birth. In situ hybridization performed on sections from whole fetuses revealed that HAGT mRNA was restricted to the developing liver and heart between E9.5 and E11.5 but became more widespread to include the developing aorta, brain, subcutaneous tissues, and vertebra at E13.5. In situ hybridization analysis on fetal kidneys from late gestation, newborn, and 2-wk-old mice demonstrated a progressive restriction of HAGT mRNA to developing cortical proximal tubular cells. These data illustrate the developmental tissue-specific regulation of HAGT expression and demonstrate that sequences present in the transgene can confer an appropriate developmental expression profile.

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.

Gene expression of central and peripheral renin-angiotensin system components upon dietary sodium intake in rats

The effects of dietary sodium intake on the gene expression of the renin-angiotensin system (RAS) were investigated in rat central and peripheral tissues in a single set of experiment. Northern and reverse transcriptase-polymerase chain reaction (RT-PCR) techniques were used to detect mRNA expression in rats fed a low- or a high-sodium diet (5 or 500 mmol Na+/kg diet) for 20 days. Plasma and renal renin levels were elevated in rats maintained on the low-sodium diet. Sodium deprivation enhanced the expression of angiotensinogen, renin, AT1A and AT1B receptor subtypes in the hypothalamus, but suppressed them in the brainstem. Kidney and adrenal levels of those mRNAs were also enhanced in the sodium-restricted rats. Both AT1A and AT1B mRNAs changed in a similar magnitude in each tissue examined upon dietary sodium intake. AT1A was the predominant receptor subtype of AT1 in all the tissues examined in the present study except the adrenal gland. The present study demonstrated that dietary sodium modulated the gene expression of the RAS components in the central and peripheral tissues. It also showed that the RAS components in the brainstem and hypothalamus were differentially expressed upon sodium deprivation. This suggests different roles of the RAS in these tissues in maintaining body fluid homeostasis in response to different sodium intakes.

Ontogeny of hormonal and excretory function of the meso- and metanephros in the ovine fetus

Using reverse-transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry we investigated the ontogeny of renin, angiotensinogen and angiotensin converting enzyme (ACE) in the mesonephros at 27 and 41 days of gestation, and the metanephros at 41 and 64 days of gestation in ovine fetuses (term is 145 to 150 days). The volume and composition of fetal urine, stored as allantoic fluid were measured in 12 fetuses at 27 days, and 13 fetuses at 41 days. Renin, angiotensinogen and ACE were identified in both meso- and metanephroi at 41 days but not in the mesonephros at 27 to 30 days. Allantoic fluid volumes were 21 +/- 3 and 45 +/- 5 ml at 27 to 30 days and 41 days, respectively. This fluid was significantly different in composition to that of amniotic fluid or maternal plasma. The results suggest that the mesonephros can substantially modify its glomerular filtrate by 27 days of gestation, and can produce local angiotensin II by 41 days.

Angiotensin II and its different receptor subtypes in placenta and fetal membranes

The recent discovery of a local renin-angiotensin system in trophoblastic tissues has raised many questions regarding its role in the physiology of normal gestation and its implications in the pathophysiology of hypertension during pregnancy. In this article, the authors first review the most interesting aspects of the chorioplacental renin-angiotensin system, dwelling on the tissue distribution of angiotensin II and its receptor subtypes in the placenta and fetal membranes of different species. The relationship between angiotensin II and other locally synthesized chorioplacental substances is also analysed and the therapeutic implications of phenomena observed in pregnancy-associated hypertension are discussed.

Developmental consequences of the renin-angiotensin system

Molecular, cellular, and physiological studies indicate that the renin-angiotensin system (RAS) is highly expressed during early kidney development. We propose that a major function of the RAS during early embryonic development is the modulation of growth processes that lead the primitive kidney into a properly differentiated and architecturally organized organ suited for independent extrauterine life. As development progresses, the RAS acquires new and overlapping functions such as the endocrine and paracrine regulation of blood pressure and renal hemodynamics. Disease states in adult mammals often result in expression of RAS genes and phenotypic changes resembling the embryonic pattern, emphasizing the importance of undertaking developmental studies. Because of their importance in health and disease, the immediate challenge is to identify the mechanisms that regulate the unique development of the RAS and its role(s) in normal and abnormal growth processes.

Immunocytochemical localization of angiotensinogen in the fetal and neonatal rat brain

The aim of this study was to define the temporal appearance and regional distribution of angiotensinogen in the fetal and neonatal rat brain. This was done by immunocytochemical localization of angiotensinogen in brains from embryonic day 16 to postnatal day 12. Immunostaining was first observed on embryonic day 18, and persisted to postnatal day 2, in the choroid plexus and ependymal cells lining the third ventricle. This initial expression of angiotensinogen at embryonic day 18 was followed at postnatal day 20 by a rapid progression of angiotensinogen staining appearing in astrocytes in the paraventricular nucleus, medial preoptic area, ventromedial and arcuate hypothalamic nuclei; these areas showed the highest astrocyte staining intensity in the brain. This was followed sequentially by staining in areas of the thalamus, midbrain, forebrain and brainstem. In general, neuroglial staining was higher in regions proximal to the cerebral ventricles and cerebral aqueduct. Neuronal angiotensinogen was observed at day postnatal day 0 and later. The most consistent immunopositive areas were in the forebrain and thalamus; in particular, the hippocampus, anterior and posterior cingulate cortex, basal and lateral amygdala, the caudate-putamen, globus pallidus, lateral septum, medial habenular nuclei and lateral thalamic nuclei. Most of the immunopositive cells in the hypothalamus and brainstem were astrocytes, while those in the cortex were almost exclusively neurons. Staining in thalamic regions was both neuronal and neuroglial. From the intensity of staining and cell density, it was determined that a rapid increase in angiotensinogen occurs between embryonic day 20 and postnatal day 0, followed by further, smaller increases postnatally. In conclusion, this study has shown that angiotensinogen, the protein from which angiotensin II is generated, is present in the rat fetal brain. The timing of its appearance supports the establishment of a renin-angiotensin system by late gestation. Its predominance in fetal hypothalamic nuclei and in thalamic, cerebellar and cortical neurons suggests major roles in prenatal fluid and electrolyte balance, in sensorimotor development and in brain maturation.

Location and secretion of brain angiotensinogen

Angiotensinogen is a glycoprotein with intriguing structural similarities to the serine proteinase inhibitors but with only one known function: to act as a substrate in the enzymatic generation of angiotensin peptides. It is expressed as a constitutive protein by the liver and various other tissues, including the brain. It is in this tissue that the expression of angiotensinogen attains its most complex and controversial manifestations. In late gestation, an unfolding of cellular expression occurs, starting at an epicentre in the eppendymal and astroglia cells of the hypothalamus, which rapidly and sequentially spreads to sub-cortical and then cortical regions, concentrating at sites of electrolyte, fluid and pressure regulation. This initial burgeoning of astroglial angiotensinogen is trailed by a wave of neuronal expression in various limbic and sensorimotor regions of the brain. The predominance of AT2 receptors in these regions suggests that the RAS actions are mediated by AT2 receptors. The angiotensinogen found in the CSF and secreted by cultures of glia and neurones is similar to the two major molecular sizes found in plasma. However, by electrophoretic separation on the basis of charge imparted by differential glycosylation, it can be shown that glia and neurones secrete distinct forms. The expression of different forms is under hormonal regulation. If these structural forms are shown to affect function, then the resulting ramifications may extend to pathological conditions, such as hypertension. Primary cell cultures of astrocytes secrete angiotensinogen constitutively and in a region-specific manner related to the size of the sub-population of secretory cells. Neurone cultures secrete angiotensinogen at about 25% the rate of hypothalamic astrocytes. The use of RT-PCR shows that both cell types express angiotensinogen mRNA. There is still an unresolved mismatch between these data and in situ hybridization histochemistry which shows expression limited to astrocytes but it is suggested that changes to more appropriate techniques will resolve any outstanding discrepancies.

Human angiotensinogen is highly expressed in astrocytes in human cortical grafts

Human fetal parietal cortical tissue was transplanted to cortical cavities in immunosuppressed rats. Protoplasmic astrocytes in the human cortical grafts highly expressed human angiotensinogen mRNA as identified with 35S-labeled and digoxigenin-labeled riboprobes combined with immunohistochemistry for glial fibrillary acidic protein. Antibodies to human specific neurofilament protein 70 KD were used to characterize neurons in the graft and fiber outgrowth into the host brain. Immunohistochemistry revealed human angiotensinogen-like immunoreactivity in many small protoplasmic astrocytes and very few large neurons. These results demonstrate that human angiotensinogen mRNA and protein is synthesized in immature human glia. We assume that angiotensinogen is transformed into angiotensin peptides, which may participate in the regulation of growth processes. The results suggest that human angiotensinogen may play a role during human embryogenesis.

Differences between perinatal angiotensin binding in the brains of SHR and WKY rats

A growing body of evidence suggests that angiotensin may have a functional role in growth and development, in addition to its classical role in the maintenance of body water homeostasis. Components of the renin-angiotensin system have been identified in the rat fetus. Because of the association between the renin-angiotensin system and hypertension, we quantified angiotensin receptor binding sites in the brains of spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats during perinatal development. Using in vitro receptor autoradiography we identified specific 125I-Sar1,Ile8 AII binding in several areas of the brains of perinatal rats of both strains and observed significant differences in the concentration of binding sites, at different ages in several brain nuclei. With the knowledge that components of the renin-angiotensin system appear early in development and are known to have an association with cellular growth, it is possible that an irregularity in this system occurring during neurogenesis could contribute to developmental abnormalities, as well as subsequent hypertension.

Regional expression of angiotensinogen mRNA in the brain of one-week-old, adult and old male rats

The purpose of this study was to investigate possible regional differences in the distribution of angiotensinogen-mRNA in the postnatal versus the aging animal using in situ hybridization and computer-assisted microdensitometry. An essentially identical regional distribution pattern of angiotensinogen-mRNA in the brains of postnatal, adult and old rats was demonstrated. Substantial differences in angiotensinogen expression were observed in brain areas of postnatal versus adult and old animals. Also large differences were seen in the ratios of angiotensinogen-mRNA levels in different brain areas within one age. The medulla of young animals contained the largest amounts of angiotensinogen-mRNA compared to hypothalamus and midbrain. In contrast, adult and old animals showed approximately the same expression levels in midbrain and medulla, whereas the largest amounts of angiotensinogen-mRNA were expressed in the hypothalamus.

The renin-angiotensin system and blood pressure regulation during infancy and childhood

The renin-angiotensin system plays multiple roles in the maintenance of normal blood pressure and renal function. The balance and integration of these roles change during development in ways that we do not yet fully understand. This article reviews the ways in which the renin-angiotensin system maintains normal cardiovascular homeostasis during development and its participation in physiologic and biochemical events.

Intracardiac detection of angiotensinogen and renin: a localized renin-angiotensin system in neonatal rat heart

There is increasing evidence that the renin-angiotensin system (RAS) modulates cardiovascular function through both blood-borne and tissue-derived components. The existence of a local RAS has been proposed in the heart based on biochemical and molecular biological studies that identify angiotensinogen and renin. We conducted the present study to determine the chamber localization of angiotensinogen and renin mRNA in neonatal rat heart and whether these components could be identified in cultured cardiomyocytes and fibroblasts obtained from neonatal rat heart. Experiments using polymerase chain reaction (PCR) indicated that whole hearts obtained from neonatal rats contained both angiotensinogen and renin mRNA. With the use of radiolabeled cDNA probes and in situ hybridization, angiotensinogen and renin transcripts were localized both in the atria and ventricles of neonatal rat hearts. Relative signal strengths for angiotensinogen were highest in the left and right ventricles. In contrast, renin signal strength was overall much lower and preferentially localized in the left ventricle. To investigate the cellular source of angiotensinogen and renin, cultured neonatal heart cardiomyocytes and ventricular fibroblasts were screened for angiotensinogen and renin messenger RNA and protein using PCR and indirect immunofluorescent staining, respectively. These experiments demonstrated that both cell types produce transcripts and the respective translation products for angiotensinogen and renin. These data suggest that the site of angiotensin II synthesis can occur at the level of the individual cardiomyocyte and fibroblast, where it may serve to directly and/or indirectly regulate cardiac rate, force, growth, and development in the neonate.

Angiotensinogen is secreted by pure rat neuronal cell cultures

Previous studies are divided between those which support a neuroglial (astrocyte) source for brain angiotensinogen and those which indicate that both astrocytes and neurones synthesize the precursor of angiotensin II. In this study, separate cultures of astrocytes and neuronal cells were prepared and established as being essentially pure by appropriate immunocytochemical cell markers. Angiotensinogen production by these cultures, as measured by a direct radioimmunoassay, was 20.74 +/- 3.62 ng angiotensinogen/10(6) cells/24 h (mean +/- S.D., n = 8) for astrocytes and 4.39 +/- 0.94 ng/10(6) cells/24 h (mean +/- S.D., n = 29) for neurones. Angiotensinogen secretion from both cell types was unaffected by treatments which stimulate the regulatory secretory pathway by modulating intracellular cAMP levels. In contrast, it was reduced from 23.20 +/- 2.14 to 8.14 +/- 1.31 ng/10(6) cells/24 h (S.E.M., n = 7) in astrocyte cultures by the constitutive pathway inhibitor, monensin. Angiotensinogen secreted by astrocytes and neurones was compared to pure angiotensinogen and that in plasma and cerebrospinal fluid (CSF) by cation-exchange mono S column chromatography. Pure angiotensinogen eluted as two separate peaks corresponding to the major forms of plasma angiotensinogen, whereas angiotensinogen in CSF and culture media coeluted with a third minor form of plasma angiotensinogen. It was concluded that neuronal cells as well as astrocytes secrete angiotensinogen which is distinctly different from plasma angiotensinogen.

The mas proto-oncogene is developmentally regulated in the rat central nervous system

The mas proto-oncogene encodes a protein with a predicted structure similar to members of the family of seven transmembrane domain spanning receptors. These receptors are thought to transduce extracellular signals to G-proteins. Angiotensin II and III have been reported to be the functional ligands for the mas oncogene-encoded receptor (Jackson et al., 1988). We show here using in situ hybridization histochemistry and RNase protection assays that mas mRNA is expressed in a subpopulation of neurons in both the adult and developing rat CNS. In the adult CNS, mas mRNA is most abundant in hippocampal pyramidal neurons and dentate granule cells; mas transcripts are also present at low levels in the cortex and thalamus. mas is first expressed in the developing rat CNS at postnatal day 1 (P1). Even at this early stage in CNS development the pattern of mas expression is similar to that seen in the adult. Although at P1 most neurons of the dentate gyrus are not yet generated and cells of the hippocampal CA fields are undergoing migration and synaptogenesis (Bayer 1980; Altman and Bayer, 1990a, 1990b, 1990c), mas is specifically expressed in these cell populations. This extremely restricted pattern of expression suggests that mas may function in determining the morphology and connections of specific cell types in the hippocampus. This function may in part be carried out by the ability of mas to link external cues to intracellular processes.

Ontogeny of angiotensinogen mRNA and angiotensin II receptors in rat brain and liver

The renin-angiotensin-system (RAS) is active in fetal and neonatal life. This study was undertaken to examine the ontogenic regulation of angiotensinogen (AT) gene expression and angiotensin II (A II) receptors in liver and brain. AT gene expression was studied in fetal, neonatal, adult and aged rats, using slot blot hybridization to quantify AT mRNA levels. During fetal life (gestational days 15-20), AT mRNA was more abundant in brain than in liver. Soon after birth, brain AT mRNA levels increased to a concentration 3 fold above fetal levels. In contrast, liver AT mRNA abundance increased 30-fold within 12 h of birth. Aging (3-20 months) resulted in a gradual decrease in AT mRNA in both the brain and liver. Liver A II receptors in the neonate were 2-fold higher than in the fetus, but returned to fetal levels by 8 weeks of age. In the brain, A II receptor abundance increased to a level 75% above fetal levels in 7 days old animals, but returned to fetal levels by 14 days of age. These studies suggest than in the fetus, the liver is not the primary source of AT but that unknown factors at parturition result in a dramatic increase in liver AT mRNA. In contrast, the more modest increases in brain AT mRNA parallel the gradual maturation of the CNS. In both tissues, further aging resulted in a gradual decrease in AT mRNA, reflecting either increased sensitivity to feedback downregulation by A II or age related increases in other extrahepatic sites of AT synthesis. Age related changes were also found in the A II receptor in both the liver and brain.

Expression of AT2 receptors in the developing rat fetus

Angiotensin II is known primarily for its effects on blood pressure and electrolyte homeostasis, but recent studies suggest that angiotensin II may play a role in the regulation of cellular growth. This study was undertaken to identify the angiotensin II receptor subtypes expressed during fetal and neonatal development and to characterize their cellular localization. Using an in situ receptor binding assay on sagittal frozen sections of fetal and neonatal rats, bound 125I-[Sar1,Ile8]-angiotensin II was visualized by film and emulsion autoradiography. Bound radioligand was detected by E11 (embryonic day 11) and maximal binding occurred by E19-21. Radioligand binding remained unaltered 30 min after birth, whereas a noticeable and stable decrease was observed 12 h postparturition. The highly abundant angiotensin II receptors were shown to be AT2 by the marked reduction in radioligand binding achieved with PD123177 (10(-7)M), a specific AT2 receptor antagonist, whereas DuP 753 (10(-5)M), an AT1 receptor antagonist, had little effect. Emulsion autoradiography showed radioligand binding in the undifferentiated mesenchyme of the submucosal layers of the intestine and stomach, connective tissue and choroid surrounding the retina, subdermal mesenchyme adjacent to developing cartilage, diaphragm, and tongue. Residual AT2 receptors were found on the dorsal subdermal region of the tongue 72 h after birth. AT1 receptors were detected in the placenta at E13 and in the aorta, kidney, lung, liver, and adrenal gland at E19-21, consistent with an adult distribution. The transient expression of AT2 receptors in the mesenchyme of the fetus suggests a role of angiotensin II in fetal development.

Changes in angiotensinogen messenger RNA in differentiating 3T3-F442A adipocytes

Angiotensinogen messenger RNA (mRNA) has been identified in both brown and white adipose tissue. Recently we have shown that when 3T3-L1 cells were treated with isobutylmethylxanthine (IBMX) to accelerate differentiation, angiotensinogen mRNA increased markedly in adipocytes as compared with preadipocytes. To determine if a correlation existed between the regulatory events associated with the differentiation process, we compared the change in angiotensinogen mRNA in spontaneously differentiating 3T3-F442A cells with two established parameters of differentiation in adipocyte cell lines. Differentiation was assessed by visual examination of cells for lipid droplets, fluorescent staining of the F-actin fibers, and increases in glycerol phosphate dehydrogenase mRNA. F-actin fibers were highly structured in preadipocytes, becoming disassembled and very disorganized as cells differentiated into adipocytes. The quantity of angiotensinogen mRNA increased as the number of lipid-containing cells increased within a culture. Glycerol phosphate dehydrogenase mRNA accumulated in differentiated adipocytes to about the same extent as angiotensinogen mRNA. Thus, increases in angiotensinogen mRNA were associated with the morphological and biochemical changes that occur during the phenotypic modulation of 3T3-F442A cells.

Development, morphology, and function of the yolk-sac placenta of laboratory rodents

A review of current knowledge of the unusual structure and several functions of the yolk-sac membranes of common laboratory rodents, viz., rats, mice, hamsters, guinea pigs and gerbils, enables a better assessment of the significance of this maternofetal exchange system in the experimental production of congenital anomalies. The anatomy of both visceral and parietal walls of the rodent yolk-sac placenta--specifically the anatomical relationships of each wall with maternal and with other fetal tissues--depends on the mode of origin and subsequent development of the yolk sac in these several species. Accordingly, the developmental biology of the rodent yolk sac is described. Since both fine structure and anatomical relationships also determine in large measure the functioning of the membrane as a whole in the absorption of selected materials either for intracellular digestion or for cellular translocation and transport to the developing embryo, the anatomy of the yolk sac is considered in detail. Similarly, since available evidence strongly suggests that teratogenic agents induce perturbations in the cellular mechanisms that control these several functions of the yolk-sac placental system in the production of birth defects, additionally an account is given of the cell biology of the membrane, i.e., endocytosis and targeting/trafficking of materials either for digestion within the epithelium at the maternal surface of the visceral yolk sac or for translocation across the yolk-sac membrane as a whole.

Angiotensinogen production by rat astroglial cells in vitro and in vivo

To investigate the production of angiotensinogen by the brain, primary cultures were prepared from the brains of one-day-old rats. Two to four weeks after plating, they were transferred to serum-free medium. The cultures, which contained approximately 15% neurons, 80% astroglia and 5% other types of cells, produced angiotensinogen at a steady rate for three to four days in serum-free medium. Cultures prepared from subcortical tissue produced more angiotensinogen than cultures prepared from cerebral cortical tissue. Angiotensinogen mRNA was also identified in those cultures. Forskolin treatment had no effect on angiotensinogen production. Astroglia-enriched cultures that contained no identifiable neurons also produced angiotensinogen and its mRNA. Astroglial cells from hypothalamus and thalamus produced more of both than astroglial cells from the cerebral cortex. In situ hybridization histochemistry on sections of the hypothalamus of adult male rats showed a diffuse distribution of cells containing angiotensinogen mRNA that was more consistent with a glial than a neuronal distribution. The data indicate that most if not all of the angiotensinogen in rat brain is produced by astrocytes.

Novel sites of expression of functional angiotensin II receptors in the late gestation fetus

In the adult, the peptide hormone angiotensin II (AII) is primarily known as a regulator of circulatory homeostasis, but recent evidence also suggests a role in cell growth. This study of AII in late gestation rat fetuses revealed the unexpected presence of receptors in skeletal muscle and connective tissue, in addition to those in recognized adult target tissues. The AII receptors in this novel location decreased by 80 percent 1 day after birth and were almost undetectable in the adult. Studies in fetal skin fibroblasts showed that the receptors were coupled to phospholipid breakdown, with concomitant increases in inositol phosphate and cytosolic calcium. The abundance, timing of expression, and unique localization of functional AII receptors in the fetus suggest a role for AII in fetal development.

Characterization of angiotensin II receptors in the rat fetus

The presence of AII receptors during early and late embryonic development was studied by binding of 125I[Sar1, Ile8] AII to whole mouse blastocysts and membrane-rich fractions from rat conceptuses, 7 to 21 days in gestation. In early mouse embryos there was no detectable binding under a variety of experimental conditions. However, in late gestation rat fetuses, specific and high affinity binding was observed, with a concentration of sites similar in membranes from whole and eviscerated fetuses. Using less than 100 micrograms of membrane protein, binding was time and temperature dependent, maintaining equilibrium from 30 to 120 min at 23 degrees C and it was enhanced by addition of Mg+2 up to 5 mM, EGTA 2 mM and dithiothreitol up to 2.5 mM. Scatchard analysis of the binding data indicated Kd values ranging between 0.7 and 0.9 nM. Binding was first detectable at day 10 (14.3 +/- 2.3 fmol/mg), increasing to 104 +/- 16, 2,625 +/- 168, 5,993 +/- 152 and 5,902 +/- 92 by days 12, 15, 18, and 21 of gestational age, respectively. Since the functional significance of these binding sites depends on the availability of the agonist ligand, acid extracts from eviscerated 10-day-old fetuses were analyzed for the presence of AII. Measurement of AII by radioimmunoassay revealed immunoreactive AII-like material (845 pg/g of tissue), with an elution pattern identical to that of AII standard in a Sephadex G-50 column. This material was bioactive, as demonstrated by its ability to displace 125I[Sar1, Ile8]AII from adrenal glomerulosa membranes, an effect which was abolished by pretreatment of the extract with AII antibody.(ABSTRACT TRUNCATED AT 250 WORDS)