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Using immunohistochemistry and quantitative in vitro autoradiography, the present study was undertaken to examine whether co-expression of pro-atherosclerotic factors, ACE, the AT(1) receptor, and iNOS, is increased in early and advanced atherosclerotic lesions of human coronary arteries. In normal coronary arteries, ACE and eNOS were strongly co-expressed in endothelial cells (ECs), whereas the AT(1) receptor was expressed in medial smooth muscle cells (SMCs). By contrast, iNOS was not expressed in ECs and SMCs. In early atherosclerotic lesions and atheromatous plaques, ACE, the AT(1) receptor and iNOS immunostaining were primarily co-localized in infiltrated macrophages and SMCs adjacent to macrophages. eNOS expression was lower in ECs than in normal arteries, and absent in accumulated macrophages and SMCs. In fibrosclerotic plaques, ACE, the AT(1) receptor, and iNOS immunostaining were still positive in macrophages as well as new microvessels within the plaques. Interestingly, SMCs in vasa vasorum of the adventitia in atheromatous and fibrosclerotic plaques were also strongly positive for AT(1) receptor and iNOS, while ECs of the vasa vasorum were positive for ACE and eNOS. The present study demonstrates that multiple pro-atherosclerotic factors ACE, AT(1) receptor and iNOS are co-localized almost exclusively in infiltrated macrophages and SMCs that have accumulated in or adjacent to early and advanced atherosclerotic plaques, while the anti-atherosclerotic enzyme eNOS is reduced in ECs. These data therefore suggest that increased formation of Ang II and iNOS in infiltrated macrophages and medial SMCs might well play important roles in the development and progression of human coronary atherosclerosis.

The female athlete triad is an increasingly prevalent condition involving disordered eating, amenorrhea, and osteoporosis. An athlete can suffer from all 3 components of the triad, or just 1 or 2 of the individual conditions. The main element underlying all the aspects of the triad is an adaptation to a negative caloric balance. Screening for these disorders should be an important component of an athlete's care. Prevention and treatment should involve a team approach, including a physician, a nutritionist, and a mental health provider., (Copyright 2010 Elsevier Inc. All rights reserved.)

Approximately one-quarter of people over the age of 65 are estimated to suffer some form of cognitive impairment, underscoring the need for effective cognitive-enhancing agents. Insulin-regulated aminopeptidase (IRAP) is potentially an innovative target for the development of cognitive enhancers, as its peptide inhibitors exhibit memory-enhancing effects in both normal and memory-impaired rodents. Using a homology model of the catalytic domain of IRAP and virtual screening, we have identified a class of nonpeptide, small-molecule inhibitors of IRAP. Structure-based computational development of an initial "hit" resulted in the identification of two divergent families of compounds. Subsequent medicinal chemistry performed on the highest affinity compound produced inhibitors with nanomolar affinities (K(i) 20-700 nM) for IRAP. In vivo efficacy of one of these inhibitors was demonstrated in rats with an acute dose (1 nmol in 1 microl) administered into the lateral ventricles, improving performance in both spatial working and recognition memory paradigms. We have identified a family of specific IRAP inhibitors that is biologically active which will be useful both in understanding the physiological role of IRAP and potentially in the development of clinically useful cognitive enhancers. Notably, this study also provides unequivocal proof of principal that inhibition of IRAP results in memory enhancement.

The angiotensin AT(4) receptor was originally defined as the specific, high-affinity binding site for the hexapeptide angiotensin IV (Ang IV). Subsequently, the peptide LVV-hemorphin 7 was also demonstrated to be a bioactive ligand of the AT(4) receptor. Central administration of Ang IV, its analogues or LVV-hemorphin 7 markedly enhance learning and memory in normal rodents and reverse memory deficits observed in animal models of amnesia. The AT(4) receptor has a broad distribution and is found in a range of tissues, including the adrenal gland, kidney, lung and heart. In the kidney Ang IV increases renal cortical blood flow and decreases Na(+) transport in isolated renal proximal tubules. The AT(4) receptor has recently been identified as the transmembrane enzyme, insulin-regulated membrane aminopeptidase (IRAP). IRAP is a type II integral membrane spanning protein belonging to the M1 family of aminopeptidases and is predominantly found in GLUT4 vesicles in insulin-responsive cells. Three hypotheses for the memory-potentiating effects of the AT(4) receptor/IRAP ligands, Ang IV and LVV-hemorphin 7, are proposed: (i) acting as potent inhibitors of IRAP, they may prolong the action of endogenous promnestic peptides; (ii) they may modulate glucose uptake by modulating trafficking of GLUT4; (iii) IRAP may act as a receptor, transducing the signal initiated by ligand binding to its C-terminal domain to the intracellular domain that interacts with several cytoplasmic proteins.

Using [(125)I]Angiotensin IV (Ang IV) for the autoradiographic localisation of oxytocinase/insulin-regulated aminopeptidase (IRAP), we demonstrate for the first time that IRAP is distributed throughout the female reproductive tract. The highest concentration of IRAP was detected in the outer myometrial layer of the uterus with lower levels in the inner myometrial layer and in the luminal epithelium. High levels of the enzyme was also detected in the inner mucosal lining of the ampulla segment of the fallopian tubes with lower levels in the interstitial and isthmus. In the ovary, a high level of IRAP was found in the corpus albicans with lower levels throughout the ovarian cortex and the surrounding connective tissue. In the uterine body of ovariectomised (OVX) ewes, oestrogen treatment resulted in a significant decrease (P<0.05) in the level of IRAP in the outer myometrium. These findings indicate an important role for IRAP in reproductive physiology in regulating the action of peptide hormones.

Central administration of angiotensin IV (Ang IV) analogues attenuates scopolamine-induced amnesia. Ang IV mediates its effects by binding to a high affinity, binding site, AT(4) receptor, that has recently been identified as insulin regulated aminopeptidase (IRAP). The purpose of this study was to examine the effect of the distinct AT(4) ligand, LVV-hemorphin-7 (LVV-H7), on scopolamine-induced learning deficits, one which involves fear-conditioning and the other spatial learning. Rats were pretreated with an intracerebroventricular (ICV) dose of scopolamine hydrobromide followed by treatment with 1 nmol LVV-H7 or artificial cerebrospinal fluid (aCSF). During the acquisition phase of the water maze task, daily ICV infusions of 1 nmol of LVV-H7 25 min after scopolamine treatment produced marked improvement in both the latency and distance swum in order to locate the submerged platform using visual cues compared to animals treated with scopolamine only. In addition, the same dose of LVV-H7 attenuated the learning deficit observed for scopolamine-treated animals in the passive avoidance task. These studies clearly demonstrate that LVV-H7, like Ang IV, is a pharmacologically active AT(4) ligand that attenuates the deleterious effects of scopolamine on learning performance in two different behavioral paradigms.

Central administration of angiotensin IV (Ang IV) or its analogues enhance performance of rats in passive avoidance and spatial memory paradigms. The purpose of this study was to examine the effect of a single bolus injection of two distinct AT4 ligands, Nle1-Ang IV or LVV-haemorphin-7, on spatial learning in the Barnes circular maze. Mean number of days for rats treated with either Nle1-Ang IV or LVV-haemorphin-7 to achieve learner criterion is significantly reduced compared with controls (P < 0.001 and P < 0.05 respectively). This is due to enhanced ability of the peptide-treated rats to adopt a spatial strategy for finding the escape hatch. In all three measures of learning performance, (1) the number of errors made, (2) the distance travelled and (3) the latency in finding the escape hatch, rats treated with either 100 pmol or 1 nmol of Nle1-Ang IV or 100 pmol LVV-haemorphin-7 performed significantly better than the control groups. As early as the first day of testing, the rats treated with the lower dose of Nle1-Ang IV or LVV-haemorphin-7 made fewer errors (P < 0.01 and P < 0.05 respectively) and travelled shorter distances (P < 0.05 for both groups) than the control animals. The enhanced spatial learning induced by Nle1-Ang IV (100 pmol) was attenuated by the co-administration of the AT4 receptor antagonist, divalinal-Ang IV (10 nmol). Thus, administration of AT4 ligands results in an immediate potentiation of learning, which may be associated with facilitation of synaptic transmission and/or enhancement of acetylcholine release.

Central administration of angiotensin IV (Ang IV) and its analogues facilitates memory retention and retrieval in normal animals and reverses amnesia induced by scopolamine or by bilateral perforant pathway lesions. Ang IV binds with high affinity and specificity to a novel binding site designated the AT(4) receptor. AT(4) receptors are abundant in the medial septum and hippocampus, a cholinergic pathway associated with memory processing. The aim of this study was to determine whether AT(4) receptors in the guinea pig hippocampus were associated with the neural input from the basal forebrain. The fimbria-fornix was lesioned by a unilateral-knife cut and the brain was processed for 125I-Ang IV binding, acetylcholinesterase, and cresyl violet staining. Unilateral lesions of the fimbria-fornix significantly reduced acetylcholinesterase staining in the ipsilateral hippocampus. The loss in cholinergic input to the hippocampus was associated with a small, but significant, reduction in 125I-Ang IV binding in the CA2 (-9%; P=0.001), and CA3 (-5%; P=0.003) of the rostral hippocampus. No other changes in 125I-Ang IV binding were observed. These results provide evidence that the majority of AT(4) receptor binding occurs in a post-synaptic locus in the guinea pig hippocampus.

The peptide hormone, angiotensin II, acts primarily via type I (AT(1)) and type II (AT(2)) angiotensin receptors. Proteolytic fragments of angiotensin II also have biological activity via these and other receptors, with actions that may mimic or antagonise angiotensin II. Most notably, a high affinity-binding site for angiotensin IV (the Val(3)-Phe(8) fragment of angiotensin II) has recently been identified as the insulin-regulated aminopeptidase (IRAP). While AT(1) and AT(2) receptors are seven transmembrane-spanning, G protein-coupled receptors with some well-established features of relevance to health and disease, the existence of separate receptor systems for angiotensin fragments offers exciting possibilities for new therapeutics to target the diverse actions of the angiotensin peptides.

Angiotensinogen, the precursor molecule for angiotensins I, II and III, and the enzymes renin, angiotensin-converting enzyme (ACE), and aminopeptidases A and N may all be synthesised within the brain. Angiotensin (Ang) AT(1), AT(2) and AT(4) receptors are also plentiful in the brain. AT(1) receptors are found in several brain regions, such as the hypothalamic paraventricular and supraoptic nuclei, the lamina terminalis, lateral parabrachial nucleus, ventrolateral medulla and nucleus of the solitary tract (NTS), which are known to have roles in the regulation of the cardiovascular system and/or body fluid and electrolyte balance. Immunohistochemical and neuropharmacological studies suggest that angiotensinergic neural pathways utilise Ang II and/or Ang III as a neurotransmitter or neuromodulator in the aforementioned brain regions. Angiotensinogen is synthesised predominantly in astrocytes, but the processes by which Ang II is generated or incorporated in neurons for utilisation as a neurotransmitter is unknown. Centrally administered AT(1) receptor antagonists or angiotensinogen antisense oligonucleotides inhibit sympathetic activity and reduce arterial blood pressure in certain physiological or pathophysiological conditions, as well as disrupting water drinking and sodium appetite, vasopressin secretion, sodium excretion, renin release and thermoregulation. The AT(4) receptor is identical to insulin-regulated aminopeptidase (IRAP) and plays a role in memory mechanisms. In conclusion, angiotensinergic neural pathways and angiotensin peptides are important in neural function and may have important homeostatic roles, particularly related to cardiovascular function, osmoregulation and thermoregulation.

The decapeptide LVV-hemorphin-7 binds with high affinity to the angiotensin IV (Ang IV) receptor (AT(4) receptor), eliciting a number of physiological effects, including cellular proliferation and memory enhancement. We have recently shown that the AT(4) receptor is identical to insulin-regulated aminopeptidase (IRAP) and that both LVV-hemorphin-7 and Ang IV inhibit the catalytic activity of IRAP. In the current study, a series of alanine-substituted and N- or C-terminally modified analogs of LVV-hemorphin-7 were evaluated for their abilities to compete for (125)I-Ang IV binding in sheep adrenal and cerebellar membranes. Selected analogs were also analyzed for binding to recombinant human IRAP and inhibition of IRAP aminopeptidase activity. C-Terminal deletions of LVV-hemorphin-7 resulted in modest changes in affinity for IRAP, whereas deletion of the first three N-terminal residues abolished binding. Monosubstitutions of Tyr(4) and Trp(6) with alanine resulted in a 10-fold reduction in affinity. Competition binding studies using recombinant human IRAP demonstrated the same rank order of affinity as obtained for the ovine tissues. All LVV-hemorphin-7 analogs tested, except for Leu-Val-Val-Tyr, inhibit the cleavage of the synthetic substrate, leucine beta-naphthylamide, by IRAP, with K(i) values between 56 and 620 nM. We find that the Val(3) residue is crucial for LVV-hemorphin-7 binding to IRAP, whereas the C-terminal domain seems to play a minor role. The current study highlights the minimal residues necessary for binding and inhibition of IRAP and provides a basis to design peptidomimetic analogs for experimental and potentially clinical use.

Although angiotensin IV (Ang IV) was thought initially to be an inactive product of Ang II degradation, it was subsequently shown that the hexapeptide markedly enhances learning and memory in normal rodents and reverses the memory deficits seen in animal models of amnesia. These central nervous system effects of Ang IV are mediated by binding to a specific site, known as the AT(4) receptor, which is found in appreciable levels throughout the brain and is concentrated particularly in regions involved in cognition. This field of research was redefined by the identification of the AT(4) receptor as the transmembrane enzyme, insulin-regulated membrane aminopeptidase (IRAP). Here, we explore the potential mechanisms by which Ang IV binding to IRAP leads to the facilitation of learning and memory.

Angiotensin-converting enzyme inhibitors (ACEi) reduce cardiovascular morbidity and mortality by improving coronary perfusion, reducing ventricular hypertrophy and remodeling, and preventing progression of coronary atherosclerosis. However, the cellular mechanisms underlying the beneficial effects of ACEi are not fully understood. We studied the in vivo effects of ACE inhibition with perindopril on cellular expression of ACE, AT(1) receptors and 2 nitric oxide synthase (NOS) isoforms, endothelial (eNOS) and inducible NOS (iNOS), in human blood vessels using quantitative in vitro autoradiography and immunocytochemistry. Seven patients with ischemic heart disease were treated with perindopril (4 mg/d) for up to 5 weeks before elective coronary bypass surgery, whereas controls did not receive the ACEi (n=7). Perindopril decreased plasma ACE by 70% and the plasma angiotensin II to angiotensin I ratio by 57% and reduced vascular ACE to approximately 65% of control levels in both endothelium and adventitia. By contrast, AT(1) receptor binding in vascular smooth muscle cells was increased by 80% in patients treated with perindopril as confirmed by immunocytochemistry. eNOS was expressed primarily in endothelial cells, whereas little iNOS expression occurred in vascular smooth muscle cells of untreated patients. Both eNOS and iNOS expression seemed to increase during perindopril treatment. These results suggest that suppression of angiotensin II formation in the vascular wall and increased expression of eNOS and iNOS during ACE inhibition may be beneficial in reversing endothelial dysfunction in patients with cardiovascular disease. Because vascular AT(1) receptor expression is increased during chronic ACE inhibition, more clinical studies are required to determine whether it is necessary to combine ACE inhibitors and AT(1) receptor antagonists in clinical management of heart failure, coronary heart disease, and hypertension

The authors identified predictors of functional disability and mortality after status epilepticus in a multivariate analysis of 83 episodes in 74 patients. Twenty-one percent (14/85) of episodes were fatal. Increased age (OR = 1.1; 95% CI, 1.0 to 1.1) and acute symptomatic seizures (OR = 6.0; 95% CI, 1.2 to 30.3) were predictors of mortality. Functional outcome at discharge deteriorated in 23% (16/69) of nonfatal episodes. Increased length of hospitalization (OR = 1.04; 95% CI, 1.0 to 1.1) and acute symptomatic seizures (OR = 3.9; 95% CI, 1.0 to 14.7) were predictors of functional disability.

Central infusion of angiotensin IV or its more stable analogues facilitates memory retention and retrieval in normal animals and reverses amnesia induced by scopolamine or by bilateral perforant pathway lesions. These peptides bind with high affinity and specificity to a novel binding site designated the angiotensin AT(4) receptor. Until now, the AT(4) receptor has eluded molecular characterization. Here we identify the AT(4) receptor, by protein purification and peptide sequencing, to be insulin-regulated aminopeptidase (IRAP). HEK 293T cells transfected with IRAP exhibit typical AT(4) receptor binding characteristics; the AT(4) receptor ligands, angiotensin IV and LVV-hemorphin 7, compete for the binding of [(125)I]Nle(1)-angiotensin IV with IC(50) values of 32 and 140 nm, respectively. The distribution of IRAP and its mRNA in the brain, determined by immunohistochemistry and hybridization histochemistry, parallels that of the AT(4) receptor determined by radioligand binding. We also show that AT(4) receptor ligands dose-dependently inhibit the catalytic activity of IRAP. We have therefore demonstrated that the AT(4) receptor is IRAP and propose that AT(4) receptor ligands may exert their effects by inhibiting the catalytic activity of IRAP thereby extending the half-life of its neuropeptide substrates.

1. The lamina terminalis, a region of the brain with a high concentration of angiotensin AT1 receptors, consists of three distinct nuclei, the median preoptic nucleus, the subfornical organ and organum vasculosum of the lamina terminalis (OVLT). These latter two regions lack a blood-brain and detect changes in plasma angiotensin (Ang) II concentration and osmolality. 2. Efferent neural pathways from the lamina terminalis to the hypothalamic paraventricular and supraoptic nuclei mediate vasopressin secretion in response to plasma hypertonicity and increased circulating levels of AngII. 3. Studies using the neurotropic virus pseudorabies, which undergoes retrograde transynaptic neuronal transport following injection into peripheral sites, show that neurons in the lamina terminalis have efferent polysynaptic neural connections to the peripheral sympathetic nervous system. Some of these neurons have been shown to have polysynaptic connections to the kidney and to express AT1 receptor mRNA. We propose that circulating AngII acts at AT1 receptors in the subfornical organ and OVLT to influence the sympathetic nervous system. It is likely that the neural pathway subserving this influence involves a synapse in the hypothalamic paraventricular nucleus. 4. The lamina terminalis may exert an inhibitory osmoregulatory influence on renin secretion by the kidney. This osmoregulatory influence may be mediated by inhibition of renal sympathetic nerve activity and appears to involve a central angiotensinergic synapse. 5. The lamina terminalis exerts an osmoregulatory influence on renal sodium excretion that is independent of the renal nerves and is probably hormonally mediated.

Recent evidence demonstrates that the fragment of angiotensin II, angiotensin II (3-8) termed angiotensin IV, binds with high affinity to a specific binding site, the AT(4) receptor. Intracerebroventricular injection of AT(4) receptor agonists improves the performance of rats in passive avoidance and spatial learning paradigms. AT(4) receptors and cholinergic neurons are closely associated in regions involved in cognitive processing, such as the hippocampus and neocortex. We therefore postulated that AT(4) receptors affect cognitive processing by modulating cholinergic neurotransmission. To test this, we examined the effect of AT(4) receptor ligands, angiotensin IV and LVV-hemorphin-7, on potassium-evoked [(3)H]acetylcholine ([(3)H]ACh) release from rat hippocampal slices. Hippocampal slices from male Sprague--Dawley rats were incubated with [(3)H]choline chloride, perfused with Krebs--Henseleit solution and [(3)H]ACh release was determined. Angiotensin IV and LVV-hemorphin-7 both potentiated depolarisation-induced [(3)H]ACh release from the rat hippocampus in a concentration-dependent manner with the maximal dose (10(-7)M) of each inducing an increase of 45+/-7.5% (P<0.01) and 95.8+/-19% (P<0.01) above control, respectively. Potentiation of release by both agonists was attenuated by the AT(4) receptor antagonist, divalinal-Ang IV. Angiotensin IV-induced potentiation was not affected by AT(1) and AT(2) receptor antagonists. These results indicate that stimulation of AT(4) receptors can potentiate depolarisation-induced release of ACh from hippocampal slices and suggest that potentiation of cholinergic transmission may be a mechanism by which AT(4) receptor ligands enhance cognition.

Angiotensin IV (Ang IV), the 3-8 fragment of angiotensin II (Ang II), binds to a distinct receptor designated the AT(4) receptor. The peptide elicits a range of vascular and central actions including facilitation of memory retention and retrieval in several learning paradigms. The aim of this study was to characterize the AT(4) receptor in a human cell line of neural origin. Receptor binding studies indicate that the human neuroblastoma cell line SK-N-MC cells express a high-affinity Ang IV binding site with a pharmacological profile similar to the AT(4) receptor: (125)I]-Ang IV and (125)I]-Nle(1)-Ang IV bind specifically to the SK-N-MC cell membranes (K(d) = 0.6 and 0.1 nM) in a saturable manner (B(max) = 1.2 pmol/mg of protein). AT(4) receptor ligands, Nle(1)-Ang IV, Ang IV and LVV-haemorphin 7 (LVV-H7), compete for the binding of [(125)I]-Ang IV or [(125)I]-Nle(1)-Ang IV to the SK-N-MC cell membranes with rank order potencies of Nle(1)-Ang IV > Ang IV > LVV-H7 with IC(50) values of 1.4, 8.7 and 59 nM ([(125)I]-Ang IV) and 1.8, 20 and 168 nM ([(125)I]-Nle(1)-Ang IV), respectively. The binding of [(125)I]-Ang IV or [(125)I]-Nle(1)-Ang IV to SK-N-MC cell membranes was not affected by the presence of GTP gamma S. Both Ang IV and LVV-H7 stimulated DNA synthesis in this cell line up to 72 and 81% above control levels, respectively. The AT(4) receptor in the SK-N-MC cells is a 180-kDa glycoprotein; under non-reducing conditions a 250-kDa band was also observed. In summary, the human neuroblastoma cell line, SK-N-MC, expresses functional AT(4) receptors that are responsive to Ang IV and LVV-H7, as indicated by an increase in DNA synthesis. This is the first human cell line of neural origin shown to express the AT(4) receptor.

In situ radioligand binding with autoradiography allows localization and quantification of bound radiolabeled ligands in tissues. This is a very sensitive technique that enables the characterization of binding kinetics and ligand specificity and the quantification of the amount of radioligand bound in different structures within the tissue. This technique is complementary to the higher resolution of immunohistochemical localization of proteins or binding sites on fixed tissue sections and in situ hybridization histochemical localization of mRNA.

Angiotensin IV and other AT4 receptor agonists, improve memory retention and retrieval in the passive avoidance and swim maze learning paradigms. Angiotensin IV binding sites (also known as the AT4 receptors) are widely distributed in guinea pig and monkey (Macaca fascicularis) brains where high densities of the binding sites have been detected in the hippocampus, neocortex and motor nuclei. However, the distribution of the binding sites in the human brain is not known. We have recently localised the angiotensin IV binding sites (AT4 receptors) in post-mortem human brain using iodinated Nle-angiotensin IV, a higher affinity and more stable analogue of angiotensin IV. This radioligand bound with relatively high affinity and specificity to angiotensin IV binding sites. In competition studies on consecutive sections through the prefrontal cortex and claustrum, angiotensin IV, Nle-angiotensin IV and LVV-hemorphin 7 competed for the binding of 125I[Nle]-angiotensin IV with nanomolar affinities. Angiotensin II and the AT1 and AT2 receptor antagonists were ineffective in competing for the binding at concentrations of up to 10 microM. We found high densities of 125I[Nle]-angiotensin IV binding sites throughout the cerebral cortex including the insular, entorhinal, prefrontal and cingulate cortices. Very high densities of the binding sites were observed in the claustrum, choroid plexus, hippocampus and pontine nucleus. Some thalamic nuclei displayed high densities of binding including the anteroprincipal, ventroanterior, anteromedial, medial dorsal and ventrolateral nuclei. The caudate nucleus, putamen, many amygdaloid nuclei and the red nucleus all displayed moderate densities of binding with a higher level detected in the substantia nigra pars compacta. In the hypothalamus, high densities binding sites were found in the ventromedial nucleus with lower levels in the dorsomedial and paraventricular nuclei. The distribution of 125I[Nle]-angiotensin IV binding sites in the human brain is similar to that found in other species and supports multiple roles for the binding sites in the central nervous system, including facilitation of memory retention and retrieval.

Background: Animal studies have demonstrated an interaction within the striatum between the angiotensin and dopaminergic systems. In rats, the angiotensin converting enzyme (ACE) inhibitor, perindopril, crosses the blood brain barrier and increases striatal dopamine synthesis and release. In humans, angiotensin type 1 receptors have been found on dopaminergic neurons in the substantia nigra and striatum. In Parkinson's disease, there is a marked reduction of these receptors associated with the nigrostriatal dopaminergic neuron loss., Aims: We performed a double blind placebo controlled crossover pilot study in seven patients to investigate the effect of the ACE inhibitor, perindopril on the clinical features of moderately severe Parkinson's disease., Results: After a four week treatment period with perindopril, patients had a faster onset in their motor response to L-dopa and a reduction in 'on phase' peak dyskinesia, p=0.021 and p=0.014 respectively. Patients also reported more 'on' periods during their waking day in their movement diary, p=0.007. Perindopril was well tolerated without any significant postural hypotension or renal dysfunction., Conclusions: These results suggest that ACE inhibitors such as perindopril may have a place in the management of motor fluctuations and dyskinesia in Parkinson's disease and justify further study.

The distributions of angiotensin AT1 and AT2 receptors have been mapped by in vitro autoradiography throughout most tissues of many mammals, including humans. In addition to confirming that AT1 receptors occur in sites known to be targets for the physiologic actions of angiotensin, such as the adrenal cortex and medulla, renal glomeruli and proximal tubules, vascular and cardiac muscle and brain circumventricular organs, many new sites of action have been demonstrated. In the kidney, AT1 receptors occur in high density in renal medullary interstitial cells. The function of these cells, which span the interstitial space between the tubules and the vasa rectae, remains to be determined. Renal medullary interstitial cells possess receptors for a number of vasoactive hormones in addition to AT1 receptors and this, in concert with their anatomic location, suggests they may be important for the regulation of fluid reabsorption or renal medullary blood flow. In the heart, the highest densities of AT1 receptors occur in association with the conduction system and vagal ganglia. In the central nervous system, high AT1 receptor densities occur in many regions behind the blood-brain barrier, supporting a role for neurally derived angiotensin as a neuromodulator. The physiologic role of angiotensin in many of these brain sites remains to be determined. The AT2 receptor also has a characteristic distribution in several tissues including the adrenal gland, heart, and brain. The role of this receptor in physiology is being elucidated, but it appears to inhibit proliferation and to participate in development. Thus, receptor-binding studies, localizing the distribution of AT1 and AT2 receptors, provide many insights into novel physiologic roles of angiotensin.

Angiotensin IV, (V-Y-I-H-P-F), binds to AT4 receptors in blood vessels to induce vasodilatation and proliferation of cultured bovine endothelial cells. This latter effect may be important not only in developing tissues but also in injured vessels undergoing remodelling. In the present study, using normal rabbit carotid arteries, we detected AT4 receptors in vascular smooth muscle cells and in the vasa vasorum of the adventitia. Very low receptor levels were observed in the endothelial cells. In keeping with the described binding specificity of AT4 receptors, unlabelled angiotensin IV competed for [125I]angiotensin IV binding in the arteries, with an IC50 of 1.4 nM, whereas angiotensin II and angiotensin III were weaker competitors. Within the first week following endothelial denudation of the carotid artery by balloon catheter, AT4 receptor binding in the media increased to approximately 150% of control tissue. AT4 receptor binding further increased in the media, large neointima and re-endothelialized cell layer to 223% at 20 weeks after injury. In view of the known trophic effects of angiotensin IV, the elevated expression of AT4 receptors, in both the neointima and media of arteries, following balloon injury to the endothelium, suggests a role for the peptide in the adaptive response and remodelling of the vascular wall following damage.

The AT4 receptor was characterized initially as a specific binding site for angiotensin IV, a C-terminal fragment of the vasoactive peptide angiotensin II. Recently, we found that LVV-hemorphin-7, a fragment of beta globin, is an abundant peptide in the brain and binds to the AT4 receptor with high affinity and specificity. In the neuroblastoma/glioma hybrid cell line, NG108-15, LVV-hemorphin-7 and angiotensin IV competed for 125I-angiotensin IV binding in a biphasic fashion with IC50 values of 1.2 x 10(-10) and 1.1 x 10(-9) M for the high-affinity site, respectively, and 6.7 x 10(-8) and 1.5 x 10(-8) M for the low-affinity site, respectively. Both peptides were internalized rapidly by the cells. However, LVV-hemorphin-7, but not angiotensin IV, elicited a 1.8-fold increase in DNA synthesis in a dose-dependent manner. Furthermore, co-incubation of the cells with an excess of angiotensin IV (10(-6) M) inhibited LVV-hemorphin-7-stimulated DNA synthesis. Therefore, whereas LVV-hemorphin-7 and angiotensin IV were capable of binding to the AT4 receptor, only LVV-hemorphin-7 elicited [3H]thymidine incorporation in NG108-15 cells. In contrast, angiotensin IV behaved as an antagonist. The current finding suggests that LVV-hemorphin-7 is a functional peptide in the central nervous system and in view of its abundance in neural tissue, compared with angiotensin IV, may be of significant physiological importance.

We have previously shown that chronic treatment with the angiotensin-converting enzyme inhibitor perindopril increased striatal dopamine levels by 2.5-fold in normal Sprague-Dawley rats, possibly via modulation of the striatal opioid or tachykinin levels. In the present study, we investigated if this effect of perindopril persists in an animal model of Parkinson's disease, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse. C57BL/6 mice were treated with the neurotoxin (30 mg/kg/day intraperitoneally) for 4 days and then left for 3 weeks to allow the degeneration of striatal dopaminergic terminals. At this time, the mice exhibited a 40% decrease in striatal dopamine content and an accompanying 46% increase in dopamine D2 receptor levels compared with control untreated mice. The dopamine content returned to control levels, and the increase in dopamine D2 receptor levels was attenuated in mice treated with perindopril (5 mg/kg/day orally for 7 days) 2 weeks after the last dose of MPTP. When the angiotensin-converting enzyme inhibitor was administered (5 mg/kg/day for 7 days) immediately after the cessation of the MPTP treatment, there was no reversal of the effect of the neurotoxin in decreasing striatal dopamine content. Our results demonstrate that perindopril is an effective agent in increasing striatal dopamine content in an animal model of Parkinson's disease.

In the uterus, bradykinin is a potent inducer of smooth muscle contraction, which is mediated by the bradykinin B2 receptor subtype. However, little is known about the distribution or regulation of this receptor in this tissue. The aim of this study was to localize the B2 receptor in the uterus and determine whether the levels of this receptor were altered during the estrous cycle and modulated by estrogen and/or progesterone in ovariectomized rats. At diestrus, uterine B2 receptors were localized to both the circular and longitudinal smooth muscle layers of the myometrium, the endometrial stroma, the glandular epithelium, and the layer subjacent to the luminal epithelium. B2 receptor levels in both myometrium and endometrium were lowest during early proestrus, when estrogen levels are low, whereas myometrial B2 receptor protein and messenger RNA levels were highest during late proestrous, when estrogen levels peak. Similar findings were observed for the estrogen-supplemented group after ovariectomy, with progesterone appearing to inhibit the estrogen-induced rise in bradykinin B2 receptor density in estrogen/progesterone-treated animals. Using in vitro receptor autoradiography employing the specific B2 receptor antagonist analog, HPP-HOE140, immunostaining with specific antipeptide antibodies generated against the B2 receptor, and in situ hybridization using a specific bradykinin B2 receptor riboprobe, our findings show a discrete distribution of the bradykinin B2 receptor throughout the different layers of the uterus and suggest that bradykinin B2 receptor levels in the rat uterus are regulated by estrogen, and possibly progesterone, in both myometrium and endometrium.

The distributions of angiotensin AT1 and AT2 receptors have been mapped by in vitro autoradiography throughout most tissues of many mammals, including humans. In addition to confirming that AT1 receptors occur in sites known to be targets for the physiologic actions of angiotensin, such as the adrenal cortex and medulla, renal glomeruli and proximal tubules, vascular and cardiac muscle, and brain circumventricular organs, many new sites of action have been demonstrated. In the kidney, AT1 receptors occur in high density in renal medullary interstitial cells. The function of these cells, which span the interstitial space between the tubules and the vasa rectae, remains to be determined. Renal medullary interstitial cells possess receptors for a number of vasoactive hormones in addition to AT1 receptors and this, in concert with their anatomical location, suggest that they may be important for the regulation of fluid reabsorption or renal medullary blood flow. In the heart, the highest densities of AT1 receptors occur in association with the conduction system and vagal ganglia. In the central nervous system, high AT1 receptor densities occur in many regions behind the blood-brain barrier, supporting a role for neurally derived angiotensin as a neuromodulator. The physiologic role of angiotensin in many of these brain sites remains to be determined. The AT2 receptor also has a characteristic distribution in several tissues including the adrenal gland, heart, and brain. The role of this receptor in physiology is being elucidated, but it appears to participate in development. Thus, receptor binding studies, localizing the distribution of AT1 and AT2 receptors, outline a number of regions where the actions of angiotensin are known but also provide many insights into novel physiologic roles of this peptide.

Adult Ren-2 gene transgenic rats, TGR(mRen-2)27, exhibit elevated circulating and kidney angiotensin II (Ang II) levels in the presence of severe hypertension. The aim of this study was to examine whether AT1 and AT2 receptors in the kidney and renal hemodynamic and tubular responses to blockade of these receptors were altered in the Ren-2 gene transgenic rats during the maintenance phase of hypertension. Renal AT1 and AT2 receptors were mapped by in vitro autoradiography (n=8), and the effects of blockade of these receptors on mean arterial pressure (MAP), heart rate (HR), and renal cortical (CBF) and medullary blood flows (MBF) were studied in anaesthetized, adult age-matched male homozygous TGR rats (n=12) and Sprague-Dawley (SD) rats (n=7). TGR rats showed higher basal MAP (P<0.001), heart and kidney weight (P<0.001), plasma renin activity (P<0.05) and plasma Ang II level (P<0.05), and CBF (P<0.05) and MBF (P<0.05) than SD rats. AT1 receptor binding was significantly increased in the glomeruli, proximal tubules, and the inner stripe of the outer medulla of TGR rats (P<0.01), while the AT2 receptor binding was low at all renal sites of TGR and SD rats. Immunohistochemistry revealed that this increased AT1 receptor labeling occurred mainly in vascular smooth muscle layer of intrarenal blood vessels including afferent and efferent arterioles, juxtaglomerular apparatus, glomerular mesangial cells, proximal tubular cells, and renomedullary interstitial cells (RMICs) in the transgenic rats. Blockade of AT1 receptors with losartan in TGR rats markedly reduced MAP to the normotensive level (P<0.001) without altering HR. Both CBF (P<0.005) and MBF (P<0.05) were significantly increased by losartan in the transgenic rats. By contrast, losartan only caused a smaller decrease in MAP and an increase in renal CBF in SD rats (P<0.05). PD 123319 was without any renal effect in both SD and TGR rats. These findings suggest that markedly increased AT1 receptors in renal vasculature, glomerular mesangial cells, and RMICs in the presence of fulminant hypertension and elevated circulating and tissue Ang II levels may play an important role in the maintenance of hypertension in the Ren-2 gene transgenic rats.

The distribution of angiotensin AT1 and AT2 receptors in the human central nervous system has been mapped and is reviewed here. The results discussed provide the anatomical basis for inferences regarding the physiological role of angiotensin in the human brain. The distribution of the AT2 receptor is very restricted in the human brain and shows a high degree of variability across species. The physiological role of this receptor in the adult central nervous system is not clear. In contrast, a high correlation exists between the distributions of AT1 receptors in the human and other mammalian brains studied. This pattern of distribution suggests that angiotensin, acting through the AT1 receptor, would act as a neuromodulator or neurotransmitter in the human central nervous system to influence fluid and electrolyte homeostasis, pituitary hormone release and autonomic control of cardiovascular function.

1. Renomedullary interstitial cells (RMIC), abundant throughout the medulla of the kidney, have been demonstrated to have binding sites for many vasoactive peptides, including atrial natriuretic peptide, endothelin, angiotensin II and bradykinin (BK). These observations would support the hypothesis that interactions between RMIC and vasoactive peptides are important in the regulation of renal function. 2. We aimed to localize the BK B2 receptor binding site to RMIC in vivo and to also demonstrate that these receptors are biologically active in vitro. 3. The present study demonstrates BK B2 binding sites on RMIC of the inner stripe of the outer medulla and the inner medulla of the rat kidney in vivo. 4. We further demonstrate that the BK B2 radioligand [125I]-HPP-Hoe140 specifically bound to rat RMIC in vitro. In addition, reverse transcription-polymerase chain reaction detected the mRNA for the BK B2 receptor subtype in cell extracts. 5. For RMIC in vitro, cAMP levels were increased at 1 min and cGMP levels were increased at 2 min after treatment with 10(-10) and 10(-7) mol/L BK, respectively. Inositol 1,4,5-trisphosphate was increased at 10 s treatment with both 10(-6) and 10(-7) mol/L BK. 6. For RMIC in vitro, BK induced an increase in cell proliferation ([3H]-thymidine incorporation) and an increase in extracellular matrix synthesis (ECM; trans-[35S] incorporation), both effects mediated by BK B2 receptors. 7. We conclude that BK B2 receptors are present on RMIC both in vivo and in vitro. These receptors are coupled to intracellular second messenger systems and, in vitro, their stimulation results in cellular proliferation and synthesis of ECM.

1. Angiotensin IV (AngIV), the (3-8) fragment of AngII, was previously believed to be an inactive metabolite. However, specific binding sites, termed AT4 receptors, have been identified in the brain and peripheral organs and the peptide has been reported to enhance memory recall in passive avoidance studies and to dilate pial and renal cortical vessels. 2. AT4 receptors are distinct from AngII AT1 and AT2 receptors with respect to function, ligand specificity and distribution. 3. In the brain, AT4 receptors are abundant in cerebral and cerebellar cortex, hippocampal formation and cholinergic systems, as well as sensory and motor systems. However, the peptide AngIV is low or undetectable in the central nervous system. This led us to search for an alternative peptide ligand of the AT4 receptor. 4. The decapeptide LVVYPWTQRF was isolated from cerebral cortex and binds with high affinity to brain AT4 receptors. This peptide sequence corresponds to an internal sequence of beta-globin and has previously been named LVV-haemorphin 7. 5. Haemorphin may represent a new class of endogenous neuropeptides, some of which interact potently with the brain AT4 receptor to elicit a range of actions.

Vasoactive peptides regulate renal medullary microcirculation and tubular function, but the localization of their receptors and mechanisms of actions are currently unknown. Using electron microscopic autoradiography, we have mapped the receptors for angiotensin II (Ang II [AT1 and AT2]), endothelin (ET(A) and ET(B)), and bradykinin (B2) in the rat renal medulla. Although these peptide receptors show distinct vascular and tubular distributions, they overlap strikingly in renomedullary interstitial cells (RMICs) of the inner stripe and the papilla. Using reverse transcription-polymerase chain reaction (RT-PCR) and Southern analysis, mRNAs for AT1A, ET(A), and B2 receptors were detected in cultured adult RMICs. Ang II increases intracellular inositol 1,4,5-triphosphate (IP3) and [Ca2+]i and stimulates [3H]thymidine incorporation and extracellular matrix (ECM) synthesis via AT1A receptors. Endothelin and bradykinin also stimulate cell proliferation and ECM synthesis in RMICs through ET(A) and B2 receptors, respectively, but the actions of endothelin are modulated by concurrent nitric oxide production. By contrast, AT2 receptor mRNA was detected only in embryonic RMICs, in which Ang II inhibits cell proliferation through this receptor. These results suggest that multiple vasoactive peptides may interact with RMICs to exert endocrine and/or paracrine influences on renal medullary microcirculation and tubular function.

In addition to its traditional role as a circulating hormone, angiotensin is also involved in local functions through the activity of tissue renin-angiotensin systems that occur in many organs, including the brain. In the brain, both systemic and presumptive neurally derived angiotensin and angiotensin metabolites act through specific receptors to modulate many functions. This review examines the distribution of these specific angiotensin receptors and discusses evidence regarding the function of angiotensin peptides in various brain regions. Angiotensin AT1 and AT2 receptors occur in characteristic distributions that are highly correlated with the distribution of angiotensin-like immunoreactivity in nerve terminals. Acting through the AT1 receptor in the brain, angiotensin has effects on fluid and electrolyte homeostasis, neuroendocrine systems, autonomic pathways regulating cardiovascular function and behavior. Angiotensin AT1 receptors are also found in many afferent and efferent components of the peripheral autonomic nervous system. The role of the AT2 receptor in the brain is less well understood, although recent knockout studies point to an involvement with behavioral and cardiovascular functions. In addition to the AT1 and AT2 receptors, receptors for other fragments of angiotensin have been proposed. The AT4 binding site, which binds angiotensin, has a widespread distribution in the brain quite distinct from that of the AT1 and AT2 receptors. It is associated with many cholinergic neuronal groups and also several sensory nuclei, but its function remains to be determined. Our discovery that another brain-derived peptide binds to the AT4 binding site in the brain and may represent the native ligand is discussed. Overall, the distribution of angiotensin receptors in the brain indicate that they play diverse and important physiological roles in the nervous system.

Angiotensin II is recognised as the principle active peptide of the renin-angiotensin system, exerting effects on fluid and electrolyte homeostasis, and cardiovascular control including neural and long term trophic effects. However, recent studies indicate that other angiotensin peptides such as angiotensin III, angiotensin II (1-7) and angiotensin IV, may have specific actions. Interestingly, recent work involving angiotensin IV demonstrates that this peptide binds to specific receptors and may be involved in memory retention and neuronal development. Furthermore, our demonstration that a globin fragment, LVV-haemorphin-7, binds with high affinity to the angiotensin IV binding site and is abundant in the brain, indicates that this may represent a novel brain neuropeptide system. It now appears, that the renin-angiotensin system is more complex than previously thought and capable of generating multiple, active peptides which elicit numerous diverse actions.

The renal medulla plays an important role in maintaining body fluid and electrolyte balance and long-term blood pressure homeostasis through its unique structural and functional properties. Among several humoral, paracrine factors or autocoids, angiotensin II (Ang II) has been implicated in the regulation of renal medullary function, including the medullary/papillary microcirculation, urine concentration, and blood pressure, but the mechanisms by which Ang II exerts influences in the renal medulla are largely unknown. The purpose of this review is to summarize the cellular localization, regulation, and functional properties of Ang II AT1 receptors in the kidney, with special emphasis on type I renomedullary interstitial cells (RMICs) in the renal medulla and cultured RMICs. High densities of AT1 receptors have been localized in type I RMICs in the inner stripe of the outer medulla by high resolution light and electron microscopic autoradiography following in vitro or in vivo labelling, or in cultured RMICs. Furthermore, reverse transcription polymerase chain reaction and Southern blot analysis now confirm that AT1 receptors in cultured RMICs are exclusively of the AT1A subtype. In cultured RMICs, Ang II markedly increases intracellular inositol 1,4,5-triphosphate (IP3) concentration, and stimulates cell proliferation and extracellular matrix synthesis, and these cellular responses are exclusively mediated by AT1 receptors. Considering the co-occurrence of high levels of renin, renin substrate angiotensinogen, and Ang II in the interstitial fluid compartment, and AT1 receptors in type I RMICs of the renal medulla, the AT1 receptor-bearing RMICs may be more responsive to the locally formed interstitial Ang II than to the circulating peptide. Since RMICs also contain the receptors for other vasoactive peptides, such as endothelin (ET[A] and ET[B]), natriuretic peptides (NPR[A] and NPR[B]), and bradykinin (B2), and synthesize prostaglandins and medullipins, they may serve as an important site for functional interactions between Ang II and other vasoactive peptides in modulating renal medullary function. More studies using different experimental approaches are therefore required to explore and elucidate the functional role of renal interstitial Ang II and AT1 receptors in RMICs in the physiological control of renal medullary function and in the pathophysiology of hypertension and progressive renal diseases.

Bradykinin exerts important influences on renal hemodynamics and tubular function by acting on renal bradykinin B2 receptors. However, the precise sites and mechanisms of its actions on the kidney are not known. To help elucidate the mechanisms of renal actions of bradykinin in vivo, we have employed high resolution electron microscopic autoradiography to localize bradykinin B2 binding sites in the rat kidney following intravenous administration of a radiolabeled ligand, 125I-HPP-Hoe140 (3-4-Hydroxyphenyl-propionyl-DArg0-[Hyp3-Thi5-D-Tic 7-Oic8]-bradykinin), a derivative of the highly selective bradykinin B2 receptor antagonist, Hoe140. In non-treated rats, bradykinin B2 binding sites were localized to the cell bodies and the luminal brush border of the proximal convoluted tubules in the cortex. In the medulla (except for the outer stripe of the outer medulla), binding occurred in the distal tubules, thin limbs of the loop of Henle, collecting ducts, peritubular capillary endothelium and renomedullary interstitial cells. To exclude the possibility that the radioligand may bind to angiotensin converting enzyme, rats were pretreated with the angiotensin converting enzyme inhibitor, perindopril. In these rats, binding to the cell bodies and the luminal brush border of the proximal convoluted tubules in the cortex was completely abolished, while binding remained unaltered in the medulla. Further studies using high performance liquid chromatography revealed that while the radioligand was degraded following systemic administration in nontreated rats, the degradation was significantly reduced in the rats pretreated chronically with perindopril. These results indicate that binding detected in the proximal tubules in the normal rats is due primarily to the tubular uptake of the degraded radioligand, and that bradykinin B2 binding sites occur predominantly in the renal tubules, vascular endothelium, and renomedullary interstitial cells of the renal medulla.

Background: ACE inhibitors are widely used in treating hypertension and heart failure, but the sites and mechanisms of ACE inhibition in human blood vessels are not understood. The present study was undertaken to assess the sites and extent of in vivo inhibition of ACE by long-term perindopril treatment in different layers of the internal mammary artery in patients with ischemic heart disease., Methods and Results: Sixteen patients with ischemic heart disease were treated either with perindopril (4 mg/d PO) for up to 36 days before surgery (n = 9) or without the inhibitor as control subjects (n = 7). The segments of the internal mammary artery were collected for measurement of vascular free and total ACE by quantitative in vitro autoradiography with 125I-351A binding. The patients treated with perindopril had lower plasma ACE (P < .001) and plasma angiotensin (Ang) II-to-Ang I ratio (P < .05). In the internal mammary artery, free ACE was similarly inhibited by perindopril in the endothelium (P < .05) and adventitia (P < .05), and the free ACE-to-total ACE ratio, an index of ACE inhibition, was markedly decreased by perindopril in parallel in the endothelium (P < .001) and adventitia (P < .001). Moreover, plasma ACE correlated highly with vascular ACE in the endothelium (r = .85, P < .001) or adventitia (r = .78, P < .001), and mean arterial pressure correlated significantly with free ACE in the endothelium (r = .52, P < .05) or adventitia (r = .53, P < .05) and with the plasma Ang II-to-Ang I ratio (r = .53, P < .05). Light microscopic autoradiographs of 125I-351A binding revealed a marked inhibition of ACE by perindopril in both layers of the vascular wall., Conclusions: The present demonstrates that long-term administration of perindopril potently inhibits both endothelial and adventitial ACE to a comparable degree in the human internal mammary artery. These results indicate that perindopril effectively penetrates the vascular wall to inhibit ACE in the adventitia, thus providing evidence that perindopril may be beneficial in inhibiting both circulating Ang II and its local formation in the vascular wall.

We have previously demonstrated that angiotensin II stimulates the release of dopamine from the normotensive rat striatum via the AT1 receptor. In this study, the effect of angiotensin II-stimulated striatal dopamine release in the spontaneous hypertensive rat was compared to normotensive controls. In the spontaneous hypertensive rat, angiotensin II stimulated dopamine release to 169 +/- 13% (P < 0.05) in the experimental period, with levels remaining high in the recovery phase, 158 +/- 16% (P < 0.05). This effect was not significantly different from the response in normotensive controls, in which angiotensin II stimulated dopamine release to 149 +/- 18% (P < 0.05) in the experimental period, with the effect also persisting through the recovery period, 244 +/- 62% (P < 0.05). Thus, despite reports of increased activity of the brain angiotensin II and dopamine systems in the spontaneous hypertensive rat, there is no evidence of abnormal regulation of the striatonigral dopamine system.

Angiotensin IV (Val-Tyr-Ile-His-Pro-Phe) has been reported to interact with specific high-affinity receptors to increase memory retrieval, enhance dopamine-induced stereotypy behavior, and induce c-fos expression in several brain nuclei. We have isolated a decapeptide (Leu-Val-Val-Tyr-Pro-Trp-Thr-Gln-Arg-Phe) from sheep brain that binds with high affinity to the angiotensin IV receptor. The peptide was isolated using 125I-angiotensin IV binding to bovine adrenal membranes to assay receptor binding activity. This peptide is identical to the amino acid sequence 30-39 of sheep betaA- and betaB-globins and has previously been named LVV-hemorphin-7. Pharmacological studies demonstrated that LVV-hemorphin-7 and angiotensin IV were equipotent in competing for 125I-angiotensin IV binding to sheep cerebellar membranes and displayed full cross-displacement. Using in vitro receptor autoradiography, 125I-LVV-hemorphin-7 binding to sheep brain sections was identical to 125I-angiotensin IV binding in its pattern of distribution and binding specificity. This study reveals the presence of a globin fragment in the sheep brain that exhibits a high affinity for, and displays an identical receptor distribution with, the angiotensin IV receptor. This globin fragment, LVV-hemorphin-7, may therefore represent an endogenous ligand for the angiotensin IV receptor in the CNS.

Bradykinin B2 receptors were localized in the sheep brain and spinal cord by quantitative in vitro autoradiography using a radiolabelled and specific bradykinin B2 receptor antagonist analogue, 3-4-hydroxyphenyl-propionyl-D-Arg0-[Hyp3,Thi5,D-Tic 7,Oic8]bradykinin, (HPP-HOE 140). This radioligand displays high affinity and specificity for bradykinin B2 receptors. The respective K(i) values of 0.32, 1.37 and 156 nM were obtained for bradykinin, HOE140 and D-Arg[Hyp3,D-Phe7,Leu8]bradykinin competing for radioligand binding to lamina II of sheep spinal cord sections. Using this radioligand, we have demonstrated the distribution of bradykinin B2 receptors in many brain regions which have not been previously reported. The highest density of bradykinin B2 receptors occur in the pleoglial periaqueductal gray, oculomotor and trochlear nuclei and the circumventricular organs. Moderate densities of receptors occur in the substantia nigra, particularly the reticular part, the posterior thalamic and subthalamic nuclei, zona incerta, the red and pontine nuclei, some of the pretectal nuclei and in discrete layers of the superior colliculus. In the hindbrain, moderate levels of bradykinin B2 receptor binding occur in the nucleus of the solitary tract, and in spinal trigeminal, inferior olivary, cuneate and vestibular nuclei. Laminae II, X and dorsal root ganglia display the most striking binding densities in the spinal cord, while the remainder of the dorsal and ventral horn display a low and diffuse density of binding. Bradykinin B2 receptors are extensively distributed throughout the sheep brain and spinal cord, not only to sensory areas but also to areas involved in motor activity.

Angiotensin-converting enzyme (ACE) inhibitors are widely used in treating hypertension and chronic heart failure, but their precise sites and mechanisms of the actions are not completely understood. In this study, we evaluated the acute and chronic in vivo inhibition of ACE by perindopril in both the endothelium and adventitia of large blood vessels including the aorta, carotid, and femoral arteries, heart, lung, and kidney by using in vitro autoradiography with [(125)I]351A as a ligand. After short-term (0.1, 0.3, and 1 mg/kg) or long-term oral administration (0.3 mg/kg), perindopril significantly inhibited plasma ACE (p < 0.001), the plasma angiotensin II (Ang II)/Ang I ratio (p < 0.01), and decreased mean arterial pressure (p < 0.001) in a dose-related manner. In the aorta, carotid, and femoral arteries, free ACE was inhibited to a similar extent in both the endothelium and adventitia by perindopril, in a dose-dependent manner, whereas total ACE in both layers of these vessels was unaltered. Similar short- and long-term ACE inhibition by perindopril was observed in the lung and heart, with somewhat greater inhibition of kidney and plasma ACE. Vascular and tissue ACE inhibition correlated highly with both plasma ACE and the plasma Ang II/Ang I ratio (r = 0.63-0.89; p < 0.001). Whereas the effects of perindopril on blood pressure, plasma Ang II/Ang I ratio, plasma and vascular ACE were all highly dose dependent, there were no significant differences on the degree of ACE inhibition observed between the three large blood vessels or between their adventitial and endothelial layers. These results demonstrate that perindopril readily penetrates the vascular wall after short- or long-term oral administration, and in a dose-dependent manner, potently inhibits both endothelial and advential vascular ACE to a comparable degree. Therefore ACE inhibitors may be beneficial in inhibiting both circulating Ang II and its local formation in the vascular wall.

The effect of chronic inhibition of the angiotensin-converting enzyme on dopamine content and release in the striatum was investigated using in vivo microdialysis in awake, freely moving rats. Rats were treated for 1 week with the angiotensin-converting enzyme inhibitor perindopril (1 mg/kg) via the drinking water, whereas the controls were given water alone. One week after perindopril treatment, striatal dopamine dialysate levels in the treated group were markedly elevated compared with control values: control, 233 +/- 43 pg/ml; perindopril, 635 +/- 53 pg/ml (p < 0.001). These results were confirmed by a complementary study in which dopamine content was measured in striatal extracts (3.5 +/- 0.4 micrograms of dopamine/g of tissue for controls compared with 9.2 +/- 2.4 micrograms of dopamine/g of tissue for the treated group; p < 0.05). In the rats that were dialyzed, angiotensin-converting enzyme levels in the striatum were decreased by 50% after perindopril treatment. Levels of dopamine D1 and D2 receptors and of preprotachykinin and tyrosine hydroxylase mRNAs were unchanged after angiotensin-converting enzyme inhibition. A small, but significant, increase was detected in striatal preproenkephalin mRNA levels in the angiotensin-converting enzyme inhibitor-treated group. These results indicate that peripherally administered angiotensin-converting enzyme inhibitors penetrate the blood-brain barrier when given chronically and modulate extracellular dopamine and striatal neuropeptide levels.

The distribution of angiotensin II AT1 and AT2 receptor subtypes were mapped in the mouse brain by in vitro autoradiography. Along with a differing distribution of AT1 and AT2 receptors in the hind brain compared to the rat, moderate densities of AT1 receptors were observed in dopamine-rich regions, namely the caudate putamen and nucleus accumbens, previously observed in the human, but not rat or rabbit. Considering our previous anatomical and functional studies demonstrating an interaction between brain angiotensin II and dopaminergic systems, the effect of chronic treatment with the dopamine antagonist, haloperidol, on AT1 and AT2 receptor levels was investigated in the mouse brain. Haloperidol treatment for 21 days resulted in an increase in angiotensin II AT1 receptor levels in the nucleus accumbens, accompanied by an increase in dopamine D2 receptors, but no change in dopamine D1 receptors. Striatal AT1 receptors did not alter with treatment, nor did AT1 or AT2 receptors in a number of brain regions not associated with dopaminergic systems, such as the median preoptic nucleus, paraventricular hypothalamic nucleus, and nucleus of the solitary tract. The present study suggests that brain angiotensin II-dopamine interactions extend beyond the known effects on the nigrostriatal dopaminergic system, to the mesocorticolimbic dopaminergic system.