Levels of angiotensin and molecular biology of the tissue renin angiotensin systems

In situ hybridization and immunohistochemistry of renal angiotensinogen in neonatal and adult rat kidneys

Recent evidence suggests that a local renin-angiotensin system is operational in the kidney and that it mediates some of the actions of angiotensin II on renal tubules. In this study the ontogeny and renal distribution of the unique precursor to angiotensin II formation, angiotensinogen, was investigated in rats by use of immunohistochemistry, immuno-electron microscopy and non-isotopic hybridization histochemistry. At the light-microscopic level, intense staining for angiotensinogen was found in the proximal convoluted tubules of the cortex, with lighter staining in the straight proximal tubules of the outer stripe. The strongest immunostaining was found in the kidneys of neonatal rats, where glomerular mesangial cells and medullary vascular bundles were also immunopositive. The angiotensinogen content of the kidneys in late gestation embryos and neonates showed the presence of angiotensinogen by day E18 and a peak content in the neonate. Non-isotopic hybridization histochemistry with biotinylated oligodeoxynucleotide probes confirmed the presence of angiotensinogen mRNA expression in the proximal convoluted tubules of the renal cortex. Electron-microscopic immunohistochemistry showed staining of relatively few electron-dense structures close to the apical membrane of proximal convoluted tubule cells in the adult kidney. In the neonatal rat kidney, angiotensinogen immunostaining at the electron-microscopic level was found throughout the proximal tubule cells and was markedly stronger than that seen in adult kidney. The presence of angiotensinogen, from embryonic day 18, in the proximal tubules, mesangial cells and vasculature of the kidney suggests multiple potential sites of intrarenal angiotensin II generation with an ontogeny in late gestation.

Molecular basis of human hypertension: the role of angiotensin

On the basis of recent advances in molecular biology and statistical genetics, it has become possible to search for chromosome regions that contain genes predisposing to hypertension and to directly link specific mutations on candidate genes to hypertension. As the human genome has been extensively mapped, highly informative, polymorphic markers are available, which can be used to detect genes in their proximity with 'hypertensinogenic' alleles. Some of these markers have been shown to be tightly linked to the genes of the renin-angiotensin system. Furthermore, the coding and regulatory regions of the genes encoding for renin, ACE, angiotensinogen and the AT1 receptor have been partially characterized. This provides a basis for further definition of specific polymorphisms within these genes that are of functional importance and that can be used to examine their contribution to the inheritance of primary hypertension. The first studies of these links have already emerged and have been reviewed in this article. Several problems arise in performing such linkage studies in human primary hypertension, however. It is difficult to define the genetic background of heterogeneous, multigenetic and multifactorial diseases such as human hypertension. Extensive studies of population genetics, including the analysis of large numbers of generations and controlled breeding experiments, cannot be performed, for obvious reasons. Blood pressure is not a convenient study trait, because it exhibits great intraindividual variance and also because of the relatively low reliability of just a few indirect measurements obtained under loosely controlled environmental conditions. Twenty-four-hour ambulatory blood pressure measurements may improve such investigations in the near future. Ravogli et al (1990) reported that the 24-hour ambulatory systolic blood pressure is higher in normotensive subjects of hypertensive parents than in normotensive subjects of normotensive parents--a finding that had not been previously reported using the conventional method of measurement. Hypertension as a trait per se is also problematic: its classification (above 140/90 mmHg) is purely artefactual, and its aetiology is highly heterogeneous. Thus, we have to keep in mind that even strong gene effects, if present in only a small subgroup of hypertensives, may not be detected in these studies. Attempts are being made to strengthen the analysis by characterizing physiologically distinct subgroups. In addition, the investigation of intermediate phenotypes, such as plasma parameters, which are more reliable and less subject to variations, may be helpful.(ABSTRACT TRUNCATED AT 400 WORDS)

Opposing actions of angiotensin-(1-7) and angiotensin II in the brain of transgenic hypertensive rats

Lack of specific antagonists to the amino-terminal heptapeptide angiotensin-(1-7) [Ang-(1-7)] prompted us to evaluate the central effects of delivering a specific affinity-purified Ang-(1-7) antibody on the blood pressure and heart rate of 12-week-old conscious homozygous female rats (n = 12) expressing the mouse submandibular Ren-2d gene [(mRen-2d)27] in their genome. Another group of transgenic hypertensive and strain-matched Sprague-Dawley controls were injected with a specific Ang II monoclonal antibody (KAA8). Cerebroventricular administration of the affinity-purified Ang-(1-7) antibody in conscious transgenic hypertensive rats caused significant dose-related elevations in blood pressure associated with tachycardia. The hypertensive response was augmented in transgenic rats studied 7 to 10 days after cessation of lisinopril therapy. Neutralization of Ang II with the Ang II antibody caused a hemodynamic response opposite to that obtained with the Ang-(1-7) antibody. All doses of the Ang II antibody produced hypotension and bradycardia. The magnitude of the depressor response was significantly augmented in transgenic rats weaned off lisinopril therapy. In contrast, central administration of either the Ang-(1-7) or Ang II antibodies had no effect on normotensive rats. Central injections of an affinity-purified IgG fraction were ineffective in both control and transgene-positive rats. These data suggest that in the brain of transgenic hypertensive rats, Ang-(1-7) opposes the action of Ang II on the central mechanism or mechanisms that contribute to the maintenance of this model of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Intrarenal angiotensin II formation in humans. Evidence from renin inhibition

The intrarenal production of angiotensin II (Ang II) as a local hormone, suggested by multiple lines of investigation, has been difficult to buttress with evidence of functional significance in humans. During studies designed to assess the renal vascular responses to the renin inhibitor enalkiren, an agent (like others in its class) with great substrate specificity, we noted in some subjects that the time course of the effect of enalkiren on renal plasma flow was not congruent with the time course of its influence on the renin-angiotensin system in the plasma compartment. We pursued this discrepancy in the current study of 18 healthy men and 9 men with essential hypertension, who each received one or more doses of enalkiren while on a fixed sodium diet. Plasma enalkiren and Ang II concentration and renal plasma flow were measured in each subject at intervals during and after discontinuation of the enalkiren infusion. Plasma enalkiren concentration fell progressively in each subject after administration was discontinued, the fall becoming evident 10 minutes after discontinuation without exception. In plasma samples obtained 90 minutes after the end of the infusion, drug levels were generally less than half of their peak value. Plasma Ang II concentration, at nadir levels by the end of the enalkiren administration, rose consistently during recovery. Renal plasma flow, in contrast, rose during infusion but did not begin to fall when enalkiren was discontinued.(ABSTRACT TRUNCATED AT 250 WORDS)

The distribution of angiotensin II type 1 receptors, and the tissue renin-angiotensin systems

Since its discovery, the functions of the renin-angiotensin system (RAS) have attracted a great deal of attention, and the roles it plays under normal conditions, and in disease, acquire a deepening significance with every year. In general, the RAS has been considered largely in terms of its roles in sodium and potassium homeostasis and the regulation of blood pressure. The continued acquisition of information on the distribution of angiotensin receptors, however, emphasizes that our interpretation needs to be widened, and it is now clear that angiotensin II has an array of functions in the tissues, which are unrelated to its systemic roles. This paracrine function is brought about by the existence of complete, localized tissue RASs, which respond to physiological demand independently from the systemic system.

Human seminal fluid contains significant quantities of prorenin: its correlation with the sperm density

The relevance of the tissue prorenin-renin-angiotensin system (PRAS) to male reproduction has been suggested by several investigators in the past. Although the presence of angiotensin converting enzyme in semen has been demonstrated, unequivocal evidence for the presence of prorenin and renin in the semen is not yet available. We have used a specific immunoradiometric assay based on an antibody directed against the pro-segment of the prorenin molecule to demonstrate that significant quantities of prorenin are present in human semen samples. Although semen is a rich source of proteases and protease inhibitors, the assay used by us, unlike the usual enzymatic renin assay, is not affected by such proteases, and their inhibitors. Furthermore, Western blotting data clearly demonstrated that prorenin is present in semen as a 48 kDa protein. In a majority of semen samples, the prorenin content was found to be several fold greater than that measured in EDTA-plasma samples. Interestingly, the level of prorenin was found to be directly proportional to the sperm density in semen samples. Our results suggest that seminal prorenin is produced locally within the male reproductive system, although its exact origin is yet to be defined, that a complete prorenin-renin-angiotensin system exists in human semen and that this system may be relevant to sperm function.

Antisense inhibition of hypertension in the spontaneously hypertensive rat

Phosphorothioated antisense oligodeoxynucleotide (ASODN) targeted to angiotensinogen mRNA was administered intracerebroventricularly in spontaneously hypertensive rats to test whether angiotensinogen reduction would lower their hypertensive blood pressures. The ASODN lowers hypertensive blood pressures to normotensive levels in spontaneously hypertensive rats; sense oligodeoxynucleotide had no effect. Administration of phosphorothioated ASODN produced a prolonged duration of lowered blood pressure. Injections of ASODN at the same dose that decreased hypertension when administered centrally did not result in blood pressure decreases when administered intra-arterially. Furthermore, angiotensinogen production was decreased in the brain stem and significantly decreased in the hypothalamus of the ASODN-treated rats (P < .05), supporting the concept of centrally mediated regulation of hypertension by an overactive brain angiotensin system. To determine the distribution of centrally administered oligodeoxynucleotides, fluorescein isothiocyanate-conjugated oligodeoxynucleotides were injected directly into the lateral ventricles. One hour later, oligodeoxynucleotides were distributed throughout the lateral and third ventricles, with tissue and cellular uptake observed in discrete cells at the injection site. This indicates that the oligodeoxynucleotides are taken up rapidly by brain cells and that they permeate the areas surrounding brain nuclei involved in central blood pressure regulation and volume homeostasis. The results confirm and extend our previous study with phosphodiester ASODN and show that phosphorothioation modification increases the duration of the response and is taken up in vivo. We conclude that with modification, ASODN inhibition of angiotensinogen mRNA translation can be used for a prolonged, profound decrease in mean arterial pressure in the spontaneously hypertensive rat through a central mechanism.

Evidence that angiotensin II is present in human monocytes

BACKGROUND

The purpose of the present study was to determine whether human monocytes and polymorphonuclear leukocytes contain angiotensins I and II.

METHODS AND RESULTS

Human mononuclear and polymorphonuclear leukocytes were isolated from blood. To identify angiotensins in human leukocytes, we performed immunocytochemistry using both alkaline phosphatase and fluorescence methods. With light microscopy immunocytochemistry with alkaline phosphatase, prominent staining of angiotensin II was observed in mononuclear leukocytes. Angiotensin I was also demonstrated in mononuclear leukocytes, but the signal was less pronounced than for angiotensin II. Polymorphonuclear leukocytes showed very little staining for angiotensin II. Fluorescence immunocytochemistry also demonstrated angiotensin II in mononuclear leukocytes. Angiotensins I and II in homogenate of leukocytes were quantified by radioimmunoassay. The concentration of angiotensins I and II in mononuclear leukocytes was 355 +/- 216 (mean +/- SEM) and 2331 +/- 106 fmol/mg protein, respectively, and the concentration in polymorphonuclear leukocytes was 36 +/- 10 and 336 +/- 120 fmol/mg protein.

CONCLUSIONS

These findings suggest that human mononuclear leukocytes contain large amounts of angiotensin II and lesser amounts of angiotensin I. Human polymorphonuclear leukocytes contain small amounts of angiotensin I and II.

Structural characterization of a diuretic peptide from the central nervous system of the leech Erpobdella octoculata. Angiotensin II Amide

Purification of a material immunoreactive to an antiserum against angiotensin II and present in the central nervous system of the pharyngobdellid leech Erpobdella octoculata was performed by reversed-phase high pressure liquid chromatography combined with both enzyme-linked immunosorbent assay and dot immunobinding assays for angiotensin II. Establishment of the amino acid sequence by Edman degradation, electrospray, and fast atom bombardement mass spectrometry measurements and enzymatic treatment by carboxypeptidase A indicated that this "central" angiotensin II-like material, the first one fully characterized in the animal kingdom, is an angiotensin II amide. This finding constitutes also the first biochemical characterization of a peptide of the angiotensin family in an invertebrate. Synthetic angiotensin II amide exerts, when injected in leeches, a diuretic effect and is, 1 and 2 h postinjection, 100-fold more potent than vertebrate angiotensin II. An identification of the proteins immunoreactive to an antiserum against angiotensin II performed at the level of both central nervous system extracts and in vitro central nervous system-translated RNA products indicated that in the two cases, two proteins were detected. Their molecular masses, which were, respectively, approximately 14 and approximately 18 kDa for the central nervous system extracts and approximately 15 and approximately 19 kDa for in vitro central nervous system-translated RNA products, differ from that of angiotensinogen (approximately 60 kDa), the precursor of vertebrate angiotensin II.

Angiotensin as neuromodulator/neurotransmitter in central control of body fluid and electrolyte homeostasis

Stimulation of central angiotensin receptors promotes, among others, drinking behaviour, stimulation of natriuresis and increased release of vasopressin. Angiotensin (ANG II)-containing pathways in the lamina terminalis and the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei, brain areas involved in the regulation of body fluid homeostasis, have been described. All these areas express predominantly AT1 receptors. The drinking response and the vasopressin release to centrally administered ANG II are mediated by AT1 receptors, while AT2 receptors exert inhibitory effects. Evidence for the involvement of the catecholaminergic and angiotensinergic pathways in the PVN and SON in mediating the ANG II-induced release of vasopressin is presented. ANG II is released in the PVN upon local osmotic stimulation and water deprivation. Finally, we present evidence that activation of central angiotensinergic receptors, water deprivation, or hypertonicity induce transcription of immediate-early genes and expression of the respective proteins in the lamina terminalis and in the PVN and SON. The summarized data implicate ANG II as a neuromodulator/neurotransmitter in central control of body fluid and electrolyte homeostasis.

Brain angiotensin and the female reproductive cycle

The results consistently show from experiment to experiment that there is a surge of brain Ang II prior to the well known preovulatory LH surge. It should be pointed out that these experiments have been carried out by two different laboratories and with the help of different experimenters and some of the experiments have been repeated. Therefore, the consistency of the results is reassuring. It does appear that Ang II increases in the brain, specifically in the hypothalamus, probably in cells of the paraventricular nucleus about 1 hour before the LH levels in plasma rise to a peak. Since LH release from the anterior pituitary gland is stimulated by the release of LHRH from the arcuate nucleus into the median eminence, the results would suggest that Ang II stimulates the release of LHRH. The peak in the OVX of Ang II treated rats is sharp and short-lasting with a second, later peak. The LH surge follows the first peak and a second rise in LH follows the second Ang II peak. These data suggest that brain Ang II synthesized and stored in the brain plays a critical role in the female reproductive cycle by initiating the LH surge. The regulation of Ang II may be by estrogen and progesterone, but as the increase in angiotensinogen mRNA was not marked, the surge of Ang II appears to result more from the sudden release of stored Ang II than its synthesis. Thus, the question is what releases Ang II. Earlier studies showed that catecholamines release Ang II from neurons and not from glia involving alpha 2 receptor blockade to increase norepinephrine by inhibiting reuptake (7). An interaction between catecholamines, Ang II and LH had also been suggested earlier (18, 19). Therefore, a series of events triggered by steroids in proestrus may begin with increases in norepinephrine activating neuronal alpha 2 receptors and precipitating release of brain Ang II. This is represented diagrammatically in Figure 15. The Ang II surge stimulates the cells containing GnRH (gonadotropin releasing hormone) in the arcuate nucleus. The effect of Ang II on multiple GnRH cells amplifies the effect and GnRH is released into the portal vessels of the pituitary to stimulate the large LH release, from gonadotrope cells in the anterior pituitary, into the plasma that produces the LH surge. The effect of the LH surge is ovulation which ends the estrogen build up.(ABSTRACT TRUNCATED AT 400 WORDS)

Antisense oligonucleotide to AT1 receptor mRNA inhibits central angiotensin induced thirst and vasopressin

Antisense oligodeoxynucleotides (AS-ODN) to AT1 receptor mRNA inhibit high blood pressure in Spontaneously Hypertensive Rats (SHR) when injected into the brain. The effect is presumably through inhibition of the actions of brain angiotensin II (Ang II). Central injection of Ang II elicits several physiological responses including release of vasopressin and motivation to drink. The angiotensin II type-I (AT1) receptor is located in brain regions which have been implicated in mediating these effects. Therefore we hypothesized that AS-ODN to AT1 mRNA would inhibit the drinking and AVP response to central administration of Ang II in adult male SHR. AS-ODN were constructed to bases +63 to +77 (15-mer) of the AT1 receptor RNA. 24 h after AS-ODN treatment (50 micrograms/4 microliters) (intracerebroventricularly, i.c.v.), the drinking response to Ang II (50 ng, i.c.v.) was significantly reduced in the SHR (P < 0.05). The drinking response to Ang II (i.c.v.) was also reduced in the Sprague-Dawley rats (P < 0.05). There was no reduction of water intake in the control animals treated with scrambled ODN (SC-ODN). Repeated injection of AS-ODN did not produce a greater reduction in drinking response. Arginine vasopressin (AVP) release to central Ang II was significantly decreased after AS-ODN treatment when compared to vehicle (P < 0.05) and to SC-ODN injections (P < 0.05). Radioligand binding assays of the hypothalamic block after AS-ODN treatment showed a significant decrease of AT1 receptor binding (P < 0.05). The results show that the antisense inhibition of brain AT1 receptor gene expression decreases the Ang II induced drinking and AVP release responses.

Converting enzyme inhibition and renal tissue angiotensin II in the rat

Multiple observations suggest local control of renal function via an intrarenal renin-angiotensin system, including evidence for local angiotensin (Ang) II production. Our first goal was to examine renal tissue Ang I:Ang II relations to ascertain whether Ang II formation differs in the circulation and in renal tissue. We have recently shown an authentic Ang II/Ang I ratio of 1.5:1 in renal lymph, the opposite of the Ang II:Ang I relation in plasma. Our second goal was to examine the influence of maximal angiotensin converting enzyme inhibition on these relations in plasma and in renal tissue. We used two converting enzyme inhibitors with differing lipid solubility, on the premise that tissue penetration and action might differ on that basis. We measured Ang I and Ang II in plasma and renal tissue of rats given an intravenous dose of either vehicle, enalapril, or ramipril, over a wide dose range, from 0.1 to 10.0 mg/kg i.v. Renal and plasma angiotensin concentrations were measured by high-performance liquid chromatography and radioimmunoassay. Whereas the Ang I concentration in normal rat plasma (273 +/- 84 fmol/mL) was over threefold the plasma Ang II concentration (83 +/- 12 fmol/mL), the ratio was reversed in the kidney (Ang II, 178 +/- 12 versus Ang I, 91 +/- 3 fmol/g; P < .001). Although ramipril and enalapril induced an indistinguishable dose-related acute fall in blood pressure and plasma Ang II concentration, lower enalapril doses were less effective in reducing renal tissue Ang I:Ang II conversion and Ang II concentration (P < .025).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin receptors in cardiovascular diseases

1. Angiotensin II (AII) plays a major role in cardiovascular function via direct actions on the vasculature, kidney, adrenal, heart, brain and sympathetic nerves. The cellular effects of AII are extensive and encompass hypertrophy, hyperplasia and the deposition of extracellular matrix. 2. The actions of AII are mediated by the AT1 and AT2 membrane receptor subtypes, and additional forms of each subtype. Evidence is emerging that selective changes in AII receptor subtypes occur in cardiovascular diseases. 3. Thyroid dysfunction increased cardiac, liver and kidney AII receptor density but decreased adrenal gland receptor density. In the heart, there was a selective increase in AT2 receptor density. 4. Diabetes increased cardiac, liver and adrenal gland AII receptor densities but decreased kidney receptor density. 5. Hypertension increased AII receptor density in the heart and kidney. A corresponding increase in receptor mRNA was prevented by selective AT1 receptor antagonists. 6. The human heart contained AII receptors in all chambers; right atrial receptor density was increased in coronary artery bypass graft patients. 7. The presence of AII receptor changes in these models of cardiac hypertrophy and hypertension raises the possibility of using orally active, subtype-selective agonists and antagonists to treat particular forms of cardiovascular diseases.

AT1 receptor subtype mediates the inhibitory effect of central angiotensin II on cerebrospinal fluid formation in the rat

The effect of central administration of angiotensin II (AII) on cerebrospinal fluid (CSF) formation was studied in pentobarbital-anesthetized, artificially-ventilated rats. CSF production was measured by the ventriculocisternal perfusion method with Blue Dextran 2000 as the indicator. Baseline value of CSF production was 3.35 +/- 0.08 microliters/min. Intracerebroventricular (i.c.v.) infusion of AII at rates of 0.5 and 5 pg/min significantly lowered (P < 0.01) CSF formation by 23% and 16%, respectively. In comparison, high peptide doses (50 and 500 pg/min) did not alter this parameter. The inhibitory effect of low AII doses on CSF formation was blocked by the i.c.v. AT1 receptor subtype antagonists, losartan and SK&F 108566 (2.4 and 2.7 ng/min, respectively), but not by the AT2 receptor subtype-specific agent, PD 123319 (3.8 ng/min). Peptide AII antagonists, [Sar1,Ile8]AII (5 ng/min), which binds to both AT1 and AT2 receptors, had a similar effect to those of AT1-specific blockers. It is concluded that AII, by controlling CSF formation, may influence the water and electrolyte balance in the brain.

Changes in renal angiotensin II receptors in spontaneously hypertensive rats by early treatment with the angiotensin-converting enzyme inhibitor captopril

We tested the hypothesis that in utero treatment with the angiotensin-converting enzyme inhibitor captopril could change the affinity, density, and/or subtypes of angiotensin II (Ang II) receptors in the kidneys of spontaneously hypertensive rats (SHR). Newborn, 7-day-old, and 4-month-old SHR and Wistar-Kyoto (WKY) rats were used. SHR and WKY rat breeders were treated with captopril (0.4 mg/mL, 100 mg/kg per day) in drinking water, and their pups were maintained on captopril treatment until experimentation. Control groups were untreated, age-matched SHR and WKY rats. The density, affinity, and subtypes of renal Ang II receptors were determined using radioligand binding techniques and receptor antagonists specific for Ang II receptor subtypes 1 and 2 (losartan, an AT1-specific antagonist, and CGP 42112B, an AT2-specific antagonist). AT1 receptor density in kidneys was higher than AT2 receptor density in both neonatal and adult rats. AT1 receptor density in kidneys increased approximately twofold from birth to 7 days of age in all groups. Newborn and 7-day-old SHR showed significantly greater Ang II receptor densities in kidneys than other rat groups because of significantly greater densities of both AT1 and AT2 receptors. At 4 months of age, there were no significant differences in Ang II receptor densities in kidneys between captopril-treated and control SHR. Our data indicate that the expression of AT1 and AT2 receptors in kidneys is differentially regulated during development. Enhanced activity of the renal renin-Ang II system in newborn and probably fetal SHR may be involved in the pathogenesis of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel inhibitory role for glucocorticoids in the secretion of angiotensinogen by C6 glioma cells

Astrocytes have been identified as the primary source of brain angiotensinogen (Ao), but the regulation of the secretion of this protein from astrocytes is poorly defined. In this study, the rat C6 glioma cell line was used as an astrocyte model to investigate the regulation of Ao secretion. C6 cultures secreted Ao at a rate of 4.05 +/- 1.52 (mean +/- SD) ng of Ao/10(6) cells/24 h as determined by a direct radioimmunoassay. This rate was not significantly altered by the hormones thyroxine, estradiol, angiotensin II, growth hormone, and prostaglandins or by increased levels of intracellular cyclic AMP. Treatment with the synthetic glucocorticoid dexamethasone (DEX; 10(-6) M) reduced the rate of Ao secretion to 1.82 +/- 0.28 ng of Ao/10(6) cells/24 h. By comparison, the basal secretion rate for rat H4 hepatoma cells was 142.4 +/- 10.0 ng of Ao/10(6) cells/24 h, and this increased fourfold (572.4 +/- 173.1 ng/10(6) cells/24 h) in the presence of 10(-6) M DEX. Both these inhibitory (C6) and stimulatory (H4) actions of DEX were dose related. The inhibition observed in C6 cells was mimicked by RU28362, a pure glucocorticoid agonist, and reversed by the antagonist RU486, demonstrating that DEX was functioning as a true glucocorticoid. The action of DEX was also antagonized by the cyclic AMP analogue N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dBcAMP) (control, DEX, and DEX + dBcAMP, 3.58 +/- 0.73, 1.69 +/- 0.82, and 4.93 +/- 1.88 ng of Ao/10(6) cells/24 h, respectively, and by the beta-adrenergic agonist isoprenaline, which stimulates cyclic AMP production.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain angiotensin receptor subtypes in the control of physiological and behavioral responses

This review summarizes emerging evidence that supports the notion of a separate brain renin-angiotensin system (RAS) complete with the necessary precursors and enzymes for the formation and degradation of biologically active forms of angiotensins, and several binding subtypes that may mediate their diverse functions. Of these subtypes the most is known about the AT1 site which preferentially binds angiotensin II (AII) and angiotensin III (AIII). The AT1 site appears to mediate the classic angiotensin responses concerned with body water balance and the maintenance of blood pressure. Less is known about the AT2 site which also binds AII and AIII and may play a role in vascular growth. Recently, an AT3 site was discovered in cultured neoblastoma cells, and an AT4 site which preferentially binds AII(3-8), a fragment of AII now referred to as angiotensin IV (AIV). The AT4 site has been implicated in memory acquisition and retrieval, and the regulation of blood flow. In addition to the more well-studied functions of the brain RAS, we review additional less well investigated responses including regulation of cellular function, the modulation of sensory and motor systems, long term potentiation, and stress related mechanisms. Although the receptor subtypes responsible for mediating these physiologies and behaviors have not been definitively identified research efforts are ongoing. We also suggest potential contributions by the RAS to clinically relevant syndromes such as dysfunctions in the regulation of blood flow and ischemia, changes in cognitive affect and memory in clinical depressed and Alzheimer's patients, and angiotensin's contribution to alcohol consumption.

Bioactive peptides in anterior pituitary cells

The anterior pituitary (AP) has been shown to contain a wide variety of bioactive peptides: brain-gut peptides, growth factors, hypothalamic releasing factors, posterior lobe peptides, opioids, and various other peptides. The localization of most of these peptides was first established by immunocytochemical methods and some of the peptides were localized in identified cell types. Although intracellular localization of a peptide may be the consequence of internalization from the plasma compartment, there is evidence for local synthesis of most of these peptides in the AP based on the identification of their messenger-RNA (mRNA). In several cases the release of the peptide from the AP cell has been shown and regulation of synthesis, storage and release have also been described. Because the amount of most of the AP peptides is very low (except for POMC peptides and galanin), endocrine functions are not expected. There is more evidence for paracrine, autocrine, or intracrine roles in growth, differentiation, and regeneration, or in the control of hormone release. To demonstrate such functions, in vitro AP experiments have been designed to avoid the interference of hypothalamic or peripheral hormones. The strategy is first to show a direct effect of the peptide after adding it to the in vitro system and, secondly, to explore if the endogenous AP peptide has a similar action by using blockers of peptide receptors or antisera immunoneutralizing the peptide.

Increased expression of angiotensin peptides in the brain of transgenic hypertensive rats

We determined the levels of angiotensin I (ANG I), angiotensin II (ANG II), and the heptapeptide angiotensin(1-7) [ANG(1-7)] in the blood and brain of female Hannover Sprague-Dawley (SD) and transgenic hypertensive rats [mRen-2]27 by radioimmunoassay and high performance liquid chromatography. Hypertension was accompanied by higher plasma concentrations of ANG II, no statistical changes in ANG(1-7), and no differences in plasma ANG I levels. In the hypothalamus of transgenic rats, concentrations of ANG II and ANG(1-7) averaged 827% and 168% above values in SD rats (p < 0.005) whereas both ANG I and ANG II increased in the medulla oblongata. The data showed that the established phase of hypertension in rats harboring the mouse Ren-2 gene is associated with overexpression of the renin-angiotensin system in brain regions participating in the endocrine regulation of blood pressure.

Insertion/deletion (I/D) polymorphism at the locus for angiotensin I-converting enzyme and myocardial infarction

Male (n = 185) and female (n = 49) survivors of myocardial infarction (MI) below 56 and 61 years of age, respectively, were compared to 366 controls with respect to distribution of genotypes in an insertion/deletion (ID) polymorphism at the angiotensin I-converting enzyme (ACE) locus. The frequency of the DD genotype (homozygosity for the deletion allele) was significantly lower among male patients than controls (22.7% versus 34.9%, p = 0.011). In a "low-risk" group, defined as having less than the sex-specific, age-adjusted median values of body mass index (BMI) and apolipoprotein B (apoB), respectively, and absence of treatment with lipid-lowering drugs, the prevalence of the DD genotype was not statistically different between male patients and controls. In a male "high-risk" group (those individuals who had not been defined as "low-risk" subjects), the prevalence of the DD genotype was 20.9% in patients and 38.3% in controls (p = 0.002). In women, no significant differences in genotype frequencies between patients and controls were found in the whole sample or in any subgroup. These results appear to be at variance with data reported recently by Cambien et al. (1992). The difference may be due to chance, undetected selection biases, different gene-environment interactions between Norway and France or Ireland, or to preferential loss of DD individuals in our male "high-risk" group.