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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Renomedullary interstitial cells (RMICs) are prominent in the inner medullary interstitium and have binding sites for several vasoactive agents, including angiotensin II (ANG II). Although the functional role of RMICs remains largely unknown, it is likely that the interaction between RMICs and vasoactive peptides is important in the regulation of renal function. The current investigation characterizes the cellular responses following treatment of RMICs with ANG II. Studies were performed on RMICs isolated from Sprague-Dawley rat kidneys. 125I-labeled [Sar1,Ile8]ANG II specifically bound to RMICs at sites determined by reverse transcription-polymerase chain reaction to be of the AT1A subtype. ANG II (10(-6) and 10(-10) M) had no effect on either basal or forskolin-stimulated adenosine 3',5'-cyclic monophosphate accumulation in RMICs but increased intracellular inositol 1,4,5-trisphosphate concentration after 10 s and intracellular calcium concentration after 18 s. For RMICs plated at low densities, ANG II (10(-6) M) induced an increase in [3H]thymidine incorporation, mediated through the AT1-receptor subtype. For RMICs plated at high densities, ANG II (10(-6) M) induced an increase in extracellular matrix synthesis as detected by trans-35S incorporation, an effect also mediated by AT1 receptors. We conclude that ANG II AT1A receptors on cultured RMICs are coupled to intracellular second messenger pathways leading to hyperplasia and synthesis of extracellular matrix.

Angiotensin IV (Val-Tyr-Ile-His-Pro-Phe) is reported to enhance apomorphine induced stereotypy and to improve memory recall through actions on specific binding sites in the central nervous system. In the present study, 10 nM angiotensin IV or angiotensin II inhibited neurite outgrowth from cultured E11 chicken paravertebral sympathetic neurones by 25%. The effects of both peptides were inhibited by a 1 microM concentration of the angiotensin IV analogues. WSU 4042, Nle1-Y-I-amide or Nle1-AIV, but not by the avian angiotensin II antagonists, [Sar1,Ile8]Ang II or CGP 42112, suggesting that the inhibition of neurite outgrowth by both peptides is mediated by the angiotensin IV binding site. These results suggest that angiotensin IV may be involved in neurite modelling and may therefore have an important role in neuronal development.

There is increasing evidence that neuropeptides have trophic functions during embryogenesis. We examined the ability of angiotensin II, substance P, somatostatin-28 and luteinising hormone-releasing hormone to influence neurite outgrowth from embryonic chick sympathetic neurons in culture. Nanomolar concentrations of angiotensin II inhibited neurite outgrowth, whereas the other peptides had no effect at similar concentrations. The effect of angiotensin II on neurite outgrowth is likely to be mediated by an atypical angiotensin receptor, as it was only weakly inhibited by [sar1,ala8]angiotensin II, and was not inhibited by losartan, an inhibitor of mammalian AT1 receptors, or PD123319, an AT2 inhibitor. Neurite outgrowth was also inhibited by angiotensin III and angiotensin IV but not by angiotensinogen I1-14. The study provides further evidence that angiotensin peptides, like classical neurotransmitters, may have trophic functions during embryogenesis.

Angiotensin IV (Val Tyr Ile His Pro Phe), administered centrally, increases memory retrieval and induces c-fos expression in the hippocampus and piriform cortex. Angiotensin IV binds to a high affinity site that is quite distinct in pharmacology and distribution from the angiotensin II AT1 and AT2 receptors and is known as the AT4 receptor. These observations suggest that the AT4 receptor may have multiple central effects. The present study uses in vitro receptor autoradiography, and employs [125I]angiotensin IV to map AT4 receptors in the macaca fascicularis brain. The distribution of the AT4 receptor is remarkable in that its distribution extends throughout several neural systems. Most striking is its localization in motor nuclei and motor associated regions. These include the ventral horn spinal motor neurons, all cranial motor nuclei including the oculomotor, abducens, facial and hypoglossal nuclei, and the dorsal motor nucleus of the vagus. Receptors are also present in the vestibular, reticular and inferior olivary nuclei, the granular layer of the cerebellum, and the Betz cells of the motor cortex. Moderate AT4 receptor density is seen in all cerebellar nuclei, ventral thalamic nuclei and the substantia nigra pars compacta, with lower receptor density observed in the caudate nucleus and putamen. Abundant AT4 receptors are also found in areas associated with cholinergic nuclei and their projections, including the nucleus basalis of Meynert, ventral limb of the diagonal band and the hippocampus, somatic motor nuclei and autonomic preganglionic motor nuclei. AT4 receptors are also observed in sensory regions, with moderate levels in spinal trigeminal, gracile, cuneate and thalamic ventral posterior nuclei, and the somatosensory cortex. The abundance of the AT4 receptor in motor and cholinergic neurons, and to a lesser extent, in sensory neurons, suggests multiple roles for the AT4 receptor in the primate brain.

There is a large body of evidence to support the concept of a relationship between brain Ang II and catecholamine systems. This interaction may participate in some central actions of Ang II such as cardiovascular control, dipsogenesis, and complex behaviours. It also extends to the nigrostriatal dopaminergic system which bear AT1 receptors, both on their cell bodies in the substantia nigra presynaptically, and on their terminals in the striatum, where Ang II can markedly potentiate DA release. This observation suggests that drugs which modulate central Ang II may be useful in regulating central dopaminergic activity.

1. Angiotensin II (AngII) receptor subtypes in adult human kidney were pharmacologically characterized by in vitro autoradiography using the AngII receptor subtype-selective antagonists, losartan and PD 123319, and the sensitivity to the reducing agent, dithiothreitol. 2. High densities of AngII AT1 receptor binding occur in the glomeruli and the inner stripe of the outer medulla, while a moderate AT1 receptor binding is localized in the proximal convoluted tubules. 3. AT2 receptor binding is observed predominantly in the intrarenal large blood vessels, including the arcuate, inter- and intra-lobular arteries, and in the renal capsule. 4. In the major renal artery, AT1 receptor binding is abundant in the media and adventitia, while AT2 receptor binding is observed mainly in the adventitia. 5. At the light microscopic level using emulsion autoradiography, AT1 receptors are localized in the glomeruli and juxtaglomerular apparatus, as expected. However, in larger renal blood vessels, including the arcuate arteries, inter- and intra-lobular arteries, intense AT2 receptor labelling occurs primarily in the adventitia, while the endothelium and vascular smooth muscle layers contain only low levels of AngII receptor binding. 6. These results indicate that the adult human kidney displays two pharmacologically distinct AngII receptor subtypes, with AT1 predominating in the glomeruli, juxtaglomerular apparatus, proximal tubules and the inner stripe of the outer medulla, while AT2 predominates in the adventitia of the arcuate and interlobular arteries and the renal capsule. The functional significance of AT2 receptor binding sites in the adventitia of adult human kidney vessels remains to be elucidated.

In the sheep spinal cord, a high density of [125I]angiotensin IV binding sites was localized to the perikaryon and processes of all somatic motor neurons, the autonomic motor neurons in the lateral horns of thoracic and lumbar segments and all dorsal root ganglia, but was low in lamina II of all dorsal horns. At supraspinal levels, [125I]angiotensin IV binding was abundant in numerous motor associated regions, with weaker binding observed in the sensory regions. This wide distribution pattern suggests an important role for the binding site in the central nervous system.

In rats with unilateral 6-hydroxydopamine lesions in the nigrostriatal pathway, injection of angiotensin II (2 nmol) into the unlesioned striatum elicited dose-related tight rotations ipsilateral to the lesion. This rotation was suppressed by coadministration of the angiotensin AT1 receptor antagonist, losartan (2 nmol), which had no significant effect when injected alone. Preadministration of the dopamine antagonist, haloperidol (2 mg/kg i.p.) completely blocked angiotensin II-induced turning at doses of 0.3-3 nmol, and partially at 10 nmol. These results further confirm the hypothesis that Ang II is intrinsically involved in modulating dopamine release in the striatum, an effect which is mediated predominantly by AT1 receptors.

The distribution of the AT1 and AT2 subtypes of angiotensin II receptor was mapped in the adult human central nervous system using quantitative in vitro autoradiography. Binding in all forebrain, midbrain, pontine, medullary and spinal cord sites where angiotensin II receptors have previously been described is of the AT1 subtype, as is binding in the small and large arteries in the adjacent meninges and in choroid plexus. By contrast, both AT1 and AT2 receptors occur in the molecular layer of the cerebellum. Angiotensin II AT1 receptors in the brain show a moderate degree of conservation across mammalian species studied so far, whereas expression of AT2 receptors is more variable, and is more restricted in the human CNS than in many other mammals. These differences between the subtype distributions in humans and other animals indicate the need for care when extrapolating the results of animal studies involving the brain angiotensin system.

There is a large body of anatomical and functional evidence supporting an interaction between brain angiotensin and central catecholamine systems. Angiotensin II AT1 receptors have been identified on dopamine containing cells in the substantia nigra and striatum of human brain using receptor autoradiography. Using in vivo microdialysis we have demonstrated that locally administered angiotensin II stimulates dopamine release from the striatum of conscious rats. Since some angiotensin receptor antagonists and angiotensin converting enzyme inhibitors can cross the blood brain barrier it is possible that they interact with the brain catecholaminergic systems.

1. The in vivo inhibition of angiotensin II (AII) receptor binding in the rat brain, kidney and adrenal was investigated after intravenous administration of the AT1-selective AII receptor antagonist losartan. 2. Male Sprague-Dawley rats were administered intravenously either vehicle, or losartan at doses of 1, 3 or 10 mg/kg. Plasma samples were collected and tissues removed at 1, 2, 8 or 24 h after administration of the antagonist. The effects of losartan on AII receptor binding were assessed by quantitative in vitro autoradiography. 3. Losartan significantly increased plasma renin activity (PRA) by six-fold and nine-fold at doses of 1 and 10 mg/kg, respectively (P < 0.05). Plasma losartan concentrations rose from 0.83 micrograms/mL at 1 mg/kg to 46.5 micrograms/mL at 10 mg/kg 1 h after administration of the drug. Plasma renin activity returned to control, whilst losartan was undetectable 24 h after injection of the antagonist. 4. In the brain, losartan produced a dose-dependent inhibition of AII receptor binding to the brain structures which express exclusively, or predominantly, AT1 receptors both outside and within the blood brain barrier. By contrast, losartan did not affect binding to the nuclei which contain exclusively, or predominantly, AT2 receptors. 5. In the kidney, losartan blocked AII receptor binding to all anatomical sites in a dose-dependent manner. The inhibition peaked at 1 h and persisted beyond 24 h despite the fact that PRA had returned to control, and losartan was not detectable in the circulation. In the adrenal gland, where AT1 and AT2 receptors occur in both the cortex and medulla, losartan caused partial inhibition at both regions. 6. These results indicate that losartan, administered intravenously at these doses, and/or its active metabolites, partially penetrate the blood brain barrier to selectively inhibit central AT1 receptors, and exert selective and prolonged blockade at AT1 receptors in peripheral target tissues.

This study was designed to evaluate the functional significance of angiotensin II (Ang II) receptors identified by previous receptor autoradiography studies to be located presynaptically on terminals of dopaminergic neurones projecting to the striatum. Microdialysis was performed in the striatum of conscious freely moving rats and dopamine and serotonin metabolites measured by HPLC with electrochemical detection. During perfusion with artificial CSF, the major extracellular dopamine metabolite identified was DOPAC with smaller concentrations of HVA. When Ang II (1 microM) was introduced into the dialysis perfusion medium, DOPAC output increased markedly, peaking at 219%, and returned to control with vehicle perfusion during the recovery period. This increase in DOPAC output with Ang II was completely blocked by co-administration of the AT1 selective antagonist, Losartan (1 microM). Administration of Losartan alone led to a significant (16%) depression of DOPAC output relative to vehicle, suggesting that dopamine release is under a tonic facilitatory influence of Ang II via the AT1 receptor subtype. Parallel, but smaller changes were seen with HVA outputs. During Ang II perfusion the output of HVA was elevated 34-79% of that in vehicle-treated rats and this effect was completely abolished by concomitant administration of Losartan. As was observed with DOPAC output, administration of Losartan alone led to a 13-24% depression of HVA output compared to vehicle perfusion. When nomifensine (10 microM) was included in the infusion fluid, dopamine was clearly measurable. Ang II perfusion increased the levels of dopamine to 225%. Values returned towards baseline during the recovery period. Ang II administration also increased (by 15% and 55%) the levels of the major serotonin metabolite, 5HIAA.(ABSTRACT TRUNCATED AT 250 WORDS)

In the human brain, receptor binding sites for angiotensin are found in the striatum and in the substantia nigra pars compacta overlying dopamine-containing cell bodies. In contrast, angiotensin-converting enzyme occurs in the substantia nigra pars reticulata and is enriched in the striosomes of the striatum. In this study, using quantitative in vitro autoradiography, we demonstrate decreased angiotensin receptor binding in the substantia nigra and striatum of postmortem brains from patients with Parkinson's disease. In the same brains the density of binding to angiotensin-converting enzyme shows no consistent change. We propose, from these results, that angiotensin receptors in the striatum are located presynaptically on dopaminergic terminals projecting from the substantia nigra. In contrast, the results support previous studies in rats demonstrating that angiotensin-converting enzyme is associated with striatal neurons projecting to the substantia nigra pars reticulata. These findings raise the possibility that newly emerging drugs that interact with the angiotensin system, particularly converting enzyme inhibitors and new nonpeptide angiotensin receptor blockers, may modulate the brain dopamine system.

Angiotensin II (Ang II) exerts a number of central actions on fluid and electrolyte homeostasis, autonomic activity, and neuroendocrine regulation. In order to evaluate likely sites where these actions are mediated, Ang II receptor binding was localized in rat brain by in vitro autoradiography with the aid of the antagonist analogue 125I-[Sar1, Ile8]Ang II. Two subtypes of Ang II receptor have been identified using recently developed peptide and nonpeptide antagonists. In the periphery, the receptor subtypes differ in distribution, second messenger coupling, and function. Brain Ang II receptor subtypes were therefore differentiated into AT-1 (type I) and AT-2 (type II) subtypes by using unlabelled nonpeptide antagonists specific for the two Ang II subtypes. AT-1 binding was determined to be that inhibited by Dup 753 (10 microM) and AT-2 binding to be that inhibited by PD 123177 (10 microM). The reducing agent dithiothreitol (DTT) decreased binding to AT-1 receptors and enhanced binding to AT-2 receptors. Many brain structures, such as the vascular organ of the lamina terminalis, subfornical organ, median preoptic nucleus, area postrema, nucleus of the solitary tract, and dorsal motor nucleus of the vagus, which are known to be related to the central actions of Ang II, contain exclusively AT-1 Ang II receptors. By contrast, the locus coeruleus, ventral and dorsal parts of lateral septum, superior colliculus and subthalamic nucleus, many nuclei of the thalamus, and nuclei of the inferior olive contain predominantly AT-2 Ang II receptors. The detailed binding characteristics of each subtype were determined by competition studies with a series of analogues of angiotensin and antagonists. The pharmacological specificity obtained in rat superior colliculus and the nucleus of the solitary tract agreed well with published data on AT-1 and AT-2 receptors, respectively. There was a high degree of correlation between the distribution of Ang II binding sites with published data on Ang II-immunoreactive fields and on the sites of Ang II-responsive neurons. The present study also reveals pharmacological heterogeneity of brain Ang II receptors. The subtype-specific receptor mapping described here is relevant to understanding the role of angiotensin peptides in the central nervous system and newly discovered central actions of nonpeptide Ang II receptor antagonists.

The anatomical distribution of receptors for angiotensin II (Ang II) and atrial natriuretic peptide (ANP) within the kidney has been investigated by in vitro autoradiography. Ang II and ANP receptor binding occurs together in several sites in the kidney, including renal vasculature, glomeruli, proximal convoluted tubule of the outer cortex, and the vasa recta bundles of the inner stripe of the outer medulla. However, in the glomeruli, Ang II receptor binding occurs predominantly in mesangial cells, while ANP receptors are localized mainly to the visceral epithelial cells. In the inner medulla, there is a moderate density of ANP receptors in marked contrast with Ang II binding which is not detected in this site. Both Ang II and ANP receptors are modulated by alterations in sodium and fluid intake, and the peptides themselves. The overlapping distribution of receptors for these two peptide hormones in several intrarenal sites may provide an anatomical basis for their physiological interaction to regulate renal hemodynamics and tubular reabsorption of sodium and water.

The effects of angiotensin II (ANG II) or angiotensin III (ANG III) on renal cortical blood flow (CBF) or papillary blood flow (PBF) were investigated in Inactin-anesthetized young rats with the use of laser-Doppler flowmetry. Infusion of equimolar pressor doses of ANG II (300 ng.kg-1.min-1 iv) or ANG III (267 ng.kg-1.min-1) decreased CBF by 31 +/- 2.6% (P less than 0.001) and 20.3 +/- 3.2% (P less than 0.01), respectively but increased PBF by 19 +/- 6.1% (P less than 0.05) and 14.6 +/- 4.4% (P less than 0.05). The ANG II-induced increase in PBF was not prevented by aortic clamping to maintain constant renal perfusion pressure or pretreatment with the prostaglandin synthase inhibitor, indomethacin. The nonpeptide ANG II receptor antagonist, DuP 753 completely abolished the systemic and intrarenal effects of ANG II. After pretreatment with a kallikrein inhibitor, aprotinin, ANG II infusion increased mean arterial pressure but did not affect PBF, suggesting that kinins, but not prostaglandins, modulate the action of systemic ANG II on PBF. We conclude that circulating ANG II induces vasoconstriction in the cortex and also promotes the intrarenal production of kinins, which act to enhance papillary blood flow.

The in vivo access of the nonpeptide angiotensin II (Ang II) antagonist, DuP 753 (10 mg kg-1, i.v.), to Ang II receptors of rat brain was investigated by in vitro autoradiography with [125I]-[Sar1, Ile8] Ang II as a ligand. DuP 753 markedly inhibited the binding to sites which contain exclusively AT1 receptors both outside and within the blood brain barrier, such as the circumventricular organs, paraventricular hypothalamic nucleus, median preoptic nucleus and nucleus of the solitary tract. However, binding to other nuclei containing AT2 receptors was not significantly inhibited. These results demonstrate that DuP 753 and/or its active metabolite readily cross the blood brain barrier in vivo and selectively inhibit binding to AT1 receptors in specific brain nuclei.

Angiotensin II (Ang II) binding sites were localized in the thalamus, basal ganglia, midbrain, and pons of the human central nervous system by in vitro autoradiography, employing 125I-[Sar1, Ile8]angiotensin II as the radioligand. High-density binding occurs in the substantia nigra pars compacta, the interpeduncular nucleus and two of the raphe nuclei, the raphe magnus, and median raphe nucleus. Moderate densities occur in the caudate nucleus, putamen, bed nucleus of the stria terminalis, rostral linear nucleus, caudal linear nucleus, dorsal and paramedian raphe nuclei, locus coeruleus, and region of the subcoeruleus, oral dorsal paramedian nucleus, and A5/periolivary region. Low levels occur in the region between the subthalamic nucleus and the zona incerta, the mediodorsal thalamic nucleus, the central gray, the lateral and medial parabrachial nuclei, and the molecular layer of the cerebellum. The high density of Ang II receptor binding in the substantia nigra occurs over pigmented, presumably dopaminergic, neurons. The binding in this site, and in the striatum, is not observed in any of the other species we have studied. It displays similar pharmacological characteristics to the Ang II receptor binding site in other regions of the human brain. Overall we demonstrate a discrete pattern of Ang II receptor binding sites in the human brain, which shows a high correlation with the distribution observed in other mammalian species.

1. Early atheroma-like lesions in rabbits are associated with increased sensitivity to serotonin. The localization and distribution of angiotensin-converting enzyme (ACE) and angiotensin II (AII) binding sites has been studied in these developing lesions by quantitative in vitro autoradiography. 2. In sham-operated control vessels, ACE was localized predominantly to intimal and adventitial sites, whereas in lesioned arteries the level of ACE detected in these regions was significantly reduced. 3. In control vessels AII receptor binding was distributed largely in the outer media, whereas in lesioned vessels AII receptor binding was dispersed throughout the media with the highest levels of binding in the outer media. 4. There was a significant amount of binding associated with ACE and with AII receptors in the extra-adventitial inflammatory tissue of lesioned arteries. 5. Apparent loss of ACE from intimal and adventitial sites may be a consequence of tissue remodelling and cellular proliferation, while the appearance of ACE in abnormal sites could play a role in AII production by the vessel wall. The role of ACE and AII in the developing atheroma-like lesions needs to be investigated further.

The distribution of binding to angiotensin II receptors in the rat heart was determined by quantitative in vitro autoradiography employing 125I-[Sar1, Ile8] angiotensin II as the radioligand. Low density binding occurs in the myocardium of both the atriums and ventricles and in the media of the aorta, pulmonary arteries and superior caval vein. Dense punctate binding is found over parasympathetic nerve bundles and some cells of the intracardiac ganglions. Binding is very low in nerves which do not stain for acetylcholinesterase. A moderate to high density of binding sites occurs throughout the conduction system, including the sinus node (low), the atrioventricular node (high) and the atrioventricular bundle (moderate). An extremely high density of binding is observed over the remnant of the arterial duct. These findings demonstrate many sites at which angiotensin II could exert its cardiac actions, including anatomical evidence supporting an action on cardiac myocytes, terminals of the vagal nerves, parasympathetic ganglion cells, and the conduction system.

Angiotensin II (Ang II) exerts a variety of actions through specific receptor binding in the kidney. These include modulation of renal hemodynamics, glomerular filtration rate (GFR), and tubular reabsorption. Quantitative in vitro autoradiography was used to localize the Ang II receptors and angiotensin converting enzyme (ACE) in rat, rabbit, and human kidney. We incubated 20 microns cryostat sections of kidney with either 125I-[Sar1]Ang II or 125I-[Sar1,Ile8]Ang II for Ang II binding or with 125I-351A for ACE localization. The resulting autoradiographs were analyzed by computerized densitometry. A high density of Ang II binding was found over glomeruli and vasa recta bundles in all species examined. The interbundle area of the outer medulla was associated with low to moderate binding of Ang II. Moderate binding of Ang II was observed over proximal convoluted tubules in the outer cortex of rat kidney. ACE was predominantly distributed in proximal convoluted tubules in all species. These studies reveal multiple sites where Ang II could modulate renal function by acting on the renal vasculature, glomeruli, vasa recta bundles, and proximal tubular sites.

1. A method for extraction, partial purification and radioimmunoassay of angiotensin II in tissues and application of the method to the kidneys of sodium-deficient rats are described. 2. Angiotensin in acid-ethanol extracts of kidney were adsorbed on to a cation-exchange resin, eluted and further purified with an immobilized angiotensin II antiserum, before radioimmunoassay. 3. Thin-layer chromatography was used, in some experiments, to separate fmol amounts of angiotensin II from its immunoreactive peptide fragments before radioimmunoassay. 4. Angiotensin II-immunoreactive material isolated from rat kidney resembled angiotensin II in many of its physicochemical properties and chromatographic mobility. 5. The concentration of immunoreactive material in kidney greatly exceeded that which could be accounted for by trapped blood and suggests that the peptide may have a local role in the organ.

1. Two-kidney one-clip hypertension was produced in rats by application of a 0.20 mm clip to the left renal artery. 2. After three weeks, the animals had mildly elevated PRA, kidney renin was elevated in the clipped kidney and markedly suppressed in the contralateral kidney when compared to values in sham-operated rats. 3. Intrarenal AII was elevated in the clipped kidney either when compared to the contralateral kidney or to values in the controls. However, in the contralateral kidney, AII was not different from controls. 4. Changes in intrarenal AII do not, therefore, always parallel those of renal renin. Failure of suppression of AII in the contralateral kidney is likely to be of pathogenetic importance in development of hypertension in this experimental model.

The drinking response during the 30 minutes following intracerebro-ventricular injection of angiotensin II (AII) (1 to 200 ng) was compared in male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto control rats (WK). SHR drank significantly less than WK at the 10, 50 and 100 ng doses. In contrast, responses to intracerebroventricular carbachol and intraperitoneal hypertonic saline were not different between SHR and WK. These agents are believed to induce drinking by mechanisms independent of angiotensin. Binding of I125-labelled AII to particles prepared from the hypothalamus, thalamus, septum and midbrain (HTSM) region was measured in one month old male and two month old female SHR and their respective age matched WK controls. No differences were found in binding between SHR and WK of either sex. These data demonstrate an impairment of drinking responses in the SHR which seem to be specific for angiotensin. This finding supports the hypothesis that the CNS angiotensin system might be abnormal in these animals.

AII occurs in the kidney at concentrations that greatly exceed those accounted for by trapped blood and is unaltered by prior perfusion of the kidneys to remove blood. Furthermore, kidney AII is unaltered by an infusion of AII at rates that double the plasma AII. The converting enzyme blocker SQ 20881 led to a fall in kidney AII and a rise in plasma renin activity (PRA). After dietary sodium deprivation, kidney AII, kidney renin, and PRA were all elevated. Sodium loading depressed plasma and kidney renin but did not alter intrarenal AII. In the two-kidney, one-clip renal hypertension model, kidney AII was elevated in the clipped kidney but unlike kidney renin was not suppressed in the contralateral kidney. Acute renal failure (ARF) induced by uranyl nitrate was associated with raised kidney AII and PRA, whereas no such changes occurred in glycerol-induced ARF. Replacement of volume losses in uranyl-nitrate-treated rats prevented the rise in PRA and the onset of ARF but not the rise in kidney AII. These findings are consistent with a local role of AII in the kidney.

The 125I-labeled agonist analog [1-sarcosine]-angiotensin II ( [Sar1]AII) bound with high specificity and affinity (Ka = 2 X 10(9) M-1) to a single class of receptor sites in rat brain. This ligand was used to analyze the distribution of AII receptors in rat brain by in vitro autoradiography followed by computerized densitometry and color coding. A very high density of AII receptors was found in the subfornical organ, paraventricular and periventricular nuclei of the hypothalamus, nucleus of the tractus solitarius, and area postrema. A high concentration of receptors was found in the suprachiasmatic nucleus of the hypothalamus, lateral olfactory tracts, nuclei of the accessory and lateral olfactory tracts, triangular septal nucleus, subthalamic nucleus, locus coeruleus, and inferior olivary nuclei. Moderate receptor concentrations were found in the organum vasculosum of the lamina terminalis, median preoptic nucleus, medial habenular nucleus, lateral septum, ventroposterior thalamic nucleus, median eminence, medial geniculate nucleus, superior colliculus, subiculum, pre- and parasubiculum, and spinal trigeminal tract. Low concentrations of sites were seen in caudate-putamen, nucleus accumbens, amygdala, and gray matter of the spinal cord. These studies have demonstrated that AII receptors are distributed in a highly characteristic anatomical pattern in the brain. The high concentrations of AII receptors at numerous physiologically relevant sites are consistent with the emerging evidence for multiple roles of AII as a neuropeptide in the central nervous system.

Angiotensin-converting enzyme (ACE) in rat brain closely resembled that in lung in its kinetics with the substrate Hip-His Leu, the inhibitors SQ 20,881 and SQ 14,225, and iun its Cl- activation profile. Modification of dietary NaCl intake was associated with marked changes in brain ACE activity. Sodium-loaded rats had lower activity of ACE in hypothalamus, striatum, and midbrain, and higher activity in spinal cord compared to controls. In sodium-restricted rats, ACE was elevated in pituitary and depressed in spinal cord. Chronic intravenous infusion of angiotensin (AII) was associated with a pattern of changes partly resembling sodium loading: ACE was depressed in hypothalamus and striatum but elevated in midbrain. After chronic intracerebroventricular infusion of AII, ACE was elevated in striatum and hippocampus, and depressed in spinal cord; a pattern of changes quite different from those associated with intravenous AII. These results show that ACE in several brain regions is sensitive to dietary sodium intake and support the hypothesis that angiotensin-containing neurons in these areas might be responsive to NaCl status of the animal. The observed changes in brain ACE do not seem to be explained in any simple manner by changes in circulating or central angiotensin II.

1. Angiotensin II (AII) has been traditionally regarded as a circulating hormone with major actions on vascular tone and aldosterone secretion. However, renin occurs in many extrarenal tissues and some evidence for local formation of AII has been presented for organs such as brain, kidney and blood vessels. 2. A peptide closely resembling AII has been detected in rapidly frozen rat adrenal. The levels found greatly exceed that which can be accounted for by blood contamination. 3. Twenty-four hours after bilateral nephrectomy, rats had undetectable plasma renin activity and plasma angiotensin II levels. At this time, adrenal AII was lower than in sham-operated animals but was still present at significant concentrations. 4. These results suggest that AII may be either concentrated or locally produced in the adrenal. The activity of the renin-angiotensin system in plasma cannot be used to make inferences regarding AII concentration at the adrenal.

1. Angiotensin II (ANG II) was measured in acid-ethanol homogenates of rapidly frozen rat kidneys by a method involving ion-exchange and immunoadsorbent purification of peptides before radioimmunoassay. 2. Concentrations of ANG II found in kidney were 10--20 times that in plasma. 3. Perfusion of the kidneys via the renal artery with isotonic sodium chloride solution or with disodium EDTA solution did not alter the concentrations of intrarenal ANG II. 4. Animals fed on a sodium-deficient diet for 8 days had markedly higher concentrations of intrarenal ANG II, plasma renin activity and kidney renin concentration than sodium-replete animals. 5. After oral sodium loading for 3 weeks, rats had suppressed plasma renin activity and kidney renin concentration but unchanged intrarenal ANG II when compared with animals on a normal sodium intake. 6. One hour after the administration of a converting enzyme inhibitor (SQ 20881) plasma renin activity was elevated, kidney renin concentration unchanged and intrarenal ANG II was depressed. 7. These results demonstrate the presence of ANG II in the extravascular compartment of the kidney. They further suggest that its quantity is influenced by sodium intake and that angiotensin I converting enzyme is essential for its formation.

Receptors for angiotensin II (AII) have been identified and characterized in many AII-responsive tissues. Those in the adrenal zona glomerulosa and vascular smooth muscle undergo dynamic regulation which appears to be mediated by changes in circulating AII, and is followed by parallel changes in sensitivity to AII. Pituitary AII receptors are mainly located in lactotrophs and corticotrophs, where they mediate specific actions of AII upon prolactin and ACTH secretion, acting in conjunction with other hypothalamic regulators. In contrast to adrenal and vascular AII receptors, those in the anterior pituitary are not affected by changes in salt balance or AII infusion. In the brain, AII receptors were increased in the subfornical organ during dehydration, but show no significant changes in the other circumventricular organs. The increase in subfornical organ receptors resembles the up-regulation of AII sites which occurs in the adrenal cortex during sodium deficiency, and could play a role in potentiating the dipsogenic effect of AII in dehydration. In the rat kidney, AII receptors have been localized in both cortex and medulla by autoradiography with 125I-[Sar1]AII. While the renal cortical receptors appear to be localized to glomeruli, the most striking feature of these studies is the abundance of specific, high-affinity AII receptors in the renal medulla.

Intravenous injection of the converting enzyme inhibitor SQ14,225 (captopril, 2 mg/kg) reduced the blood pressure of anesthetized, spontaneously hypertensive rats (SHR) progressively over a 3-hour period. An indistinguishable fall in blood pressure occurred in SHR that were bilaterally nephrectomized 1 hour prior to injection of the converting enzyme inhibitor. In the nephrectomized animals, plasma renin activity (PRA) had fallen to less than 30% of its initial values at the time of injection. Injection of the vehicle alone had no effect on blood pressure in either anephric or intact SHR. The converting enzyme inhibitor produced no significant change in the blood pressure of either intact or anephric normotensive Wistar-Kyoto (NT-WK) rats. Infusions of Sar1-Ala8-angiotensin II (saralasin, 10 micrograms/kg-1/min-1) similarly reduced blood pressure of both intact and anephric SHR. These results indicate that captopril and saralasin lower blood pressure in the SHR by some mechanism(s) independent of the kidneys, circulating renin, or bradykinin potentiation. It is suggested that angiotensin II, locally produced at some critical tissue site(s), is involved in the maintenance of raised blood pressure in SHR.

1. Rat adrenal zona glomerulosa cells were incubated in Krebs Ringer bicarbonate medium containing bovine serum albumin. Aldosterone production was measured by radioimmunoassay. 2. Both [Asp1, Ile5]-angiotensin II ('free acid') and (Asn1, Val5]-antiotensin II ('amide'), (10(-5) mol/l), stimulated aldosterone output but the free acid compound produced a larger increase in steroid output than the amide. 3. This difference in steroidogenic activity could not be explained by differences in purity or initial concentration or by stimulation of the contaminating fasciculata cells. 4. However, serial bioassays of the media revealed that the amide form of angiotensin was degraded more rapidly than the free acid form. 5. The different potency of these two forms of angiotensin II could explain some of the reported discrepancies of the action of angiotensin II on rat adrenal tissue or cells in vitro.

Plasma-membrane receptors for angiotensin II (AII) have been identified in many AII-responsive tissues involved in the control of blood pressure via direct or indirect actions on vascular contractility. The specific, high-affinity receptors for AII in adrenal zona glomerulosa, vascular smooth muscle, kidney, brain, and anterior pituitary gland exhibit generally similar binding properties. However, the AII receptors in adrenal zona glomerulosa and vascular smooth muscle undergo reciprocal regulatory changes during alterations in sodium intake. These appear to be mediated by changes in circulating AII and are accompanied by parallel changes in sensitivity to AII. The AII receptors in the anterior pituitary gland are located in lactotrophs and corticotrophs and mediate the stimulatory actions of AII upon prolactin and ACTH secretion, acting in conjunction with other hypothalamic regulators. The anterior pituitary receptors are not affected by changes in sodium balance or AII infusion, in contrast to adrenal and vascular AII receptors, but exhibit similar ligand-binding properties to the sites present in other tissues. In the brain, AII receptors are present in several discrete regions and are particularly concentrated in the circumventricular organs. During dehydration, AII receptors are increased in the subfornical organ, but show no significant changes in the other circumventricular organs. The increase in subfornical-organ receptors is analogous to the up-regulation of AII sites in the adrenal cortex during sodium deficiency and may have a potentiating action upon the dipsogenic role of AII during dehydration. Mapping of AII receptors of the brain by topical autoradiography has revealed a highly characteristic pattern of distribution in brain regions concerned with drinking, adrenergic control, blood-pressure regulation, and hypothalamic control of pituitary-hormone secretion. In the rat kidney, AII receptors have been localized in the cortex and medulla by topical autoradiography with 125I-[Sar1]AII. The renal cortical receptors appear to be localized in glomeruli, whereas the AII receptors in the renal medulla are distributed diffusely in medullary tissue and also as localized radiating stripes which correspond to the vasa rectae bundles. The location of the renal receptors for AII in cortical and medullary sites emphasizes the multiplicity of actions of the octapeptide upon the individual compartments of the kidney.