Participation of angiotensin II in learning and memory. I. Interaction of angiotensin II with saralasin

The effects of the octapeptide angiotensin II (AT II) on acquisition and retention in active avoidance tasks in shuttle-box-trained rats were studied. AT II at doses of 0.1, 0.5 and 1 microgram administered intracerebroventricularly (i.c.v.) 15 min before training facilitated learning and retention. AT II injected immediately after training also improved retention when tests were given 24 h post-trial. Saralasin at a dose of 1 microgram i.c.v. administered 15 min before training did not influence acquisition but antagonized the learning-facilitating effect of AT II. Saralasin at a dose of 5 micrograms injected immediately after training improved retention but abolished the retention-facilitating effect of AT II. It is suggested that the AT II effects on memory processes in active avoidance tasks are realized through specific angiotensin receptors in the brain structures.     

Peripherally applied candesartan inhibits central responses to angiotensin II in conscious rats

In the brain, angiotensin II (Ang II) induces various effects such as blood pressure increase, the release of arginine vasopressin (AVP) and drinking behaviour. In the present study, we investigated the ability of the angiotensin II type-I (AT(1)) receptor antagonist, candesartan, administered peripherally, to block the central effects of Ang II.Experiments were performed in conscious rats instrumented with an intracerebroventricular (i.c.v.) cannula or a guide cannula into the paraventricular nucleus (PVN) and arterial and femoral catheters. Candesartan was administered intravenously (i.v.) at doses of 0.01, 0.1, 1 or 10 mg/kg. Controls received vehicle (0.05 N Na(2)CO(3)). The drinking response ( n=10-11 per group), the pressor response ( n=7-8) and the release of AVP into the circulation ( n=10-11) following i.c.v. Ang II (100 ng) were measured 0.5, 2, 4 and 24 h following i.v. drug application. Candesartan inhibited the central responses to i.c.v. injected Ang II dose- and time-dependently. At the highest dose (10 mg/kg), the drinking and pressor responses and the release of AVP in response to i.c.v. Ang II were completely blocked at 4 h and still markedly inhibited 24 h after the antagonist application (by 85%, 48% and 86%, respectively). The lowest dose of the antagonist was without effect. In a further experiment, the release of AVP induced by microinjection of Ang II (100 ng) into the PVN was determined before and 4 h after administration of vehicle or candesartan (1 mg/kg, i.v.). Candesartan completely blocked the AVP release into the circulation induced by Ang II microinjection into the PVN.Our results demonstrate that candesartan administered peripherally effectively inhibits responses mediated by AT(1) receptors localised in periventricular brain regions as well as inside the blood-brain-barrier.     

Alzheimer's, angiotensin IV and an aminopeptidase

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 or LVV-hemorphin 7 (LVV-H7) markedly enhances learning and memory in normal rodents and reverse memory deficits observed in animal models of amnesia. The high affinity binding site has a broad distribution in the brain including areas such as the hippocampus that are involved in memory processing. The high affinity Ang IV binding site (AT(4) receptor) has been identified as the transmembrane enzyme, insulin-regulated membrane aminopeptidase (IRAP). Insulin-regulated aminopeptidase is a type II integral membrane spanning protein belonging to the M1 family of aminopeptidases and in insulin-responsive cells colocalizes with GLUT4 in specific intra-cellular vesicles. Both Ang IV and LVV-H7 are competitive inhibitors of IRAP catalytic activity and are not substrates of the enzyme.     

Losartan potassium, a nonpeptide antagonist of angiotensin II, chronically administered p.o. does not readily cross the blood-brain barrier.

Recently several novel nonpeptide antagonists of angiotensin II (Ang II) have been identified. One of these, losartan potassium (formerly DuP 753) was developed as an orally active and highly selective antagonist for Ang II. As it is inhibited by sulfhydryl agents, it is specific for the AT1 receptor subtype. Since Ang II has both central and peripheral effects, we investigated whether losartan, given p.o. chronically, crosses the blood-brain barrier. The effects of chronic administration of losartan orally (p.o.) at 3 mg/kg per day for three days on the dipsogenic and pressor responses to a pre-established dose of Ang II i.v.t. (50 ng) were studied. Three series of experiments were carried out using conscious normotensive Sprague-Dawley rats. The rats were injected with Ang II intraventricularly (i.v.t.) before and after treatment of losartan p.o. and blood pressure and drinking responses measured. The experiments established that 3 mg/kg losartan p.o. for 3 days antagonized pressor effects of Ang II intravenously (i.v.), but did not antagonize the pressor or drinking effects of Ang II i.v.t. Daily water intake significantly increased with chronic losartan p.o.. Since chronic administration of losartan p.o. was able to block the effects of Ang II i.v. but had no effect on Ang II i.v.t. we conclude that losartan potassium does not readily cross the blood-brain barrier using this dose regimen.     

Participation of angiotensin receptors in acute hypoxia in mice. I. Effects of angiotensin peptide receptor ligands saralasin and sarmesin.

The effects of angiotensin II (Ang II) and angiotensin receptor ligands sarmesin ([Sar1, Tyr(Me)4] Ang II) and saralasin ([Sar1, Ala8] Ang II) administered intracerebroventricularly (i.c.v.) on acute anoxic hypoxia were studied in mice. The interactions of these ligands and of amastatin (an aminopeptidase A inhibitor) after pretreatment with Ang II and sarmesin, respectively, were also studied. Ang II decreased the latency to hypoxia-induced convulsive seizures and altered survival time (increase or decrease depending on the dose). Sarmesin and saralasin significantly increased the latency to seizures as well as survival time. Pretreatment with saralasin and sarmesin antagonized the Ang II effect on the latency to seizures. Both drugs increased the Ang II effect on the survival time. Amastatin tended to increase the effect of sarmesin on the survival time. Taken together, the results suggest that the antihypoxic effect of sarmesin and saralasin is most likely due to an action on Ang II receptors, with the agents behaving as partial agonists.     

Effect of intraventricular infusion of an angiotensin II antagonist on I-angiotensin II binding in rats

The effects of chronic (six day) intracerebroventricular (i.c.v.) infusion of an angiotensin II antagonist, sarcosine¹, isoleucine⁸ angiotensin II ([Sar¹,Ile⁸]Ang II), (500 ng/μl per hour) was studied. Specific ¹²⁵I-Ang II binding site density and binding affinity in the hypothalamus-thalamus-septum-midbrain (H-T-S-M) region of the brain and the adrenal medulla did not differ significantly between [Sar¹,Ile⁸]Ang II treated and control (0.9% saline) rats. However, ¹²⁵I-Ang II binding to the adrenal cortex was significantly reduced by i.c.v. infusion of [Sar¹,Ile⁸]Ang II. The drinking response to microinjection of Ang II was blunted for up to seven days of [Sar¹,Ile⁸]Ang II infusion. Thus, although [Sar¹,Ile⁸]Ang II effectively blocked the central Ang II receptors, chronic infusion of this Ang II antagonist did not appear to cause alterations in brain H-T-S-M Ang II receptors, suggesting that brain Ang II receptors in normal rats do not undergo homologous regulation.     

Assessment of biological activity of novel peptide analogues of angiotensin IV

Objectives Angiotensin IV (Ang IV) is a metabolite of angiotensin II which acts on specific AT₄ receptors identified as the enzyme insulin regulated aminopeptidase (IRAP). The transduction process of these receptors is unresolved, but Ang IV inhibits the aminopeptidase activity. Ang IV improves cognition in animal models thus there is a desire to develop metabolically stable analogues for further development. Methods Peptide analogues of Ang IV were obtained commercially or synthesised. Each peptide was tested in vitro for its ability to inhibit the aminopeptidase activity (IRAP) of mouse brain homogenates and for its effects on isolated rat uterine smooth muscle. Key findings [Des‐Val¹]‐Ang IV, acetylated‐Ang IV‐amide, Ang IV‐amide and [des‐His⁴]‐Ang IV all inhibited IRAP. [Sar¹, Ile⁸]‐Angiotensin II (10 µm ) had an effect greater than that of Ang IV or any of the other analogues studied. In isolated uterine smooth muscle, angiotensins II and IV induced contractions, which could be antagonised by an AT₁‐receptor antagonist. None of the novel peptides induced uterine smooth muscle contractions, but [Sar¹, des Arg²‐Gly⁸]‐angiotensin II showed significant antagonism of the contractile effects of angiotensin II and carboxyamide‐terminated Ang IV‐NH₂ showed antagonism of Ang IV‐induced contractions. Conclusions This study provides five novel inhibitors of IRAP worthy of assessment in behavioural models of learning and memory. The analogues are devoid of AT₁ receptor agonist properties, and the carboxyamide analogue presents an opportunity to elucidate the mechanism of action of Ang IV as, like Ang IV, it inhibits IRAP, but antagonises the effects of Ang IV on isolated smooth muscle.     

Interaction of angiotensin II and adenosine A1 and A2A receptor ligands on the writhing test in mice

The effects of adenosine A1 and A2A receptor agonists and antagonists administered intraperitoneally (i.p.) and their interaction with angiotensin II (Ang II) administered intracerebroventricularly (i.c.v.) were studied in mice using the acetic acid-induced abdominal constriction test. Ang II (0.1 microg/mouse) induced antinociception in this model. The adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA; 0.05, 0.25 and 0.5 mg/kg) also showed a well-developed antinociceptive effect. Ang II (0.1 microg/mouse) administered 5 min before CPA (0.25 mg/kg) decreased the number of writhes, i.e., it enhanced the antinociceptive effect of CPA. Losartan, an AT1 receptor antagonist (25 microg/mouse i.c.v.), enhanced the antinociceptive effect of CPA, while the AT2 receptor antagonist 1-[-4-(dimethylamino)-3-methylphenylmethyl]-5-diphenylacetyl)-4,5,6,7-tetrahydro 1H-4-imidazol [4,5c]pyridine-6 carboxylic acid, ditrifluoroacetate, dihydrate (PD 123319; 10 microg/mouse) had less effect. 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.1 mg/kg), an adenosine A1 receptor antagonist, exhibited a pronociceptive effect and did not change the antinociceptive effect of Ang II. The adenosine A2A receptor agonist PD-125944 (DPMA; 0.1, 0.5 and 1 mg/kg) showed pronounced antinociceptive effect. Ang II (0.1 microg/mouse) did not significantly influence the antinociceptive effect of DPMA (0.1 mg/kg). The A2A receptor antagonist 3,7-dimethyl-1-propargilxanthine (DMPX; 0.1 mg/kg) had no effect on the number of writhes and did not influence the effect of Ang II. These data indicate that the antinociceptive effect of Ang II interacts with that produced by adenosine A1 receptor agonist.     

Brain angiotensin AT1 receptors as specific regulators of cardiovascular reactivity to acute psychoemotional stress

1. Cardiovascular reactivity, an abrupt rise in blood pressure (BP) and heart rate in response to psychoemotional stress, is a risk factor for heart disease. Pharmacological and molecular genetic studies suggest that brain angiotensin (Ang) II and AT(1) receptors are required for the normal expression of sympathetic cardiovascular responses to various psychological stressors. Moreover, overactivity of the brain AngII system may contribute to enhanced cardiovascular reactivity in hypertension. 2. Conversely, brain AT(1) receptors appear to be less important for the regulation of sympathetic cardiovascular responses to a range of stressors involving an immediate physiological threat (physical stressors) in animal models. 3. Apart from threatening events, appetitive stimuli can induce a distinct, central nervous system-mediated rise in BP. However, evidence indicates that brain AT(1) receptors are not essential for the regulation of cardiovascular arousal associated with positively motivated behaviour, such as anticipation and the consumption of palatable food. The role of central AT(1) receptors in regulating cardiovascular activation elicited by other types of appetitive stimuli remains to be determined. 4. Emerging evidence also indicates that brain AT(1) receptors play a limited role in the regulation of cardiovascular responses to non-emotional natural daily activities, sleep and exercise. 5. Collectively, these findings suggest that, with respect to cardiovascular arousal, central AT(1) receptors may be involved primarily in the regulation of the defence response. Therefore, these receptors could be a potential therapeutic target for selective attenuation of BP hyperreactivity to aversive stressors, without altering physiologically important cardiovascular adjustments to normal daily activities, sleep and exercise.     

The drinking response of the chicken to peripheral and central administration of angiotensin 11

Intravenous injection of Ang II (val⁵ angiotensin II amide) elicited an immediate drinking response in the domestic fowl which lasted at least 20 minutes. The minimal dosage needed was 300 μg. Intracranial injection of 10 μg Ang II through cannulas implanted in the anterior diencephalon caused a significant increase in water intake. The minimal intracranial dosage of Ang II which evoked drinking was 2.5 μg. Intracranial injection of isotonic KCl inhibited the drinking response induced by intravenously injected Ang II when administered simultaneously. This suggests that drinking caused by both intravenous or intracranial injection of Ang II is activated through identical brain regions. The positive drinking response of the chicken to repeated consecutive intracranial injections of Ang II declined from the first injection through the following ones.     

A comparison of the characteristics of angiotensin receptors in the renal and mesenteric vascular beds of the anesthetized cat.

Experiments were performed in anesthetized cats to compare the characteristics of angiotensin receptors in the renal and mesenteric vascular beds. Injection of either angiotensin II (Ang II; 0.3-30 ng) or angiotensin III (Ang III; 0.3-30 ng) directly into the superior mesenteric or renal artery caused dose-related, reproducible reductions in mesenteric and renal blood flow, respectively. Ang II and Ang III were equipotent as vasoconstrictors in both vascular beds. The peptide angiotensin receptor antagonists saralasin and Ile7-Ang III (1 microgram/kg/min intravenously, i.v.) and the nonpeptide angiotensin receptor antagonist DuP 753 (3 mg/kg plus 20 micrograms/kg/min i.v.) caused a rightward displacement of dose-response curves to Ang II or Ang III in both the mesenteric and renal vasculature. Vasoconstrictor responses to Ang II or Ang III in either vascular bed were blocked to similar extents by each antagonist. In separate cats, the dose of the antagonists required to cause a 10-fold rightward displacement of the Ang II dose-response curve (DR10) in both vascular beds was determined. The DR10 values indicated that the potency of each antagonist was similar in the renal and mesenteric vascular beds. These results provide no evidence to suggest that angiotensin receptors mediating vasoconstriction in the renal and mesenteric vasculature have different characteristics.     

Importance of the sympathetic nervous system in blood pressure elevation by subpressor intraventricular NaCl and angiotensin II in the rat.

The present study was performed to examine the effect of chemical sympathectomy with guanethidine on the BP change and humoral factors in rats which received continuous and concomitant infusion of i.c.v. hypertonic NaCl with i.v. Ang II, both at subpressor doses for 7 days. Male rats were divided into 3 groups which received the following infusions using an osmotic minipump at a rate of 1 microliter/min: Group 1 (n = 11), 0.15 M NaCl i.c.v. and Ang II (5.4 pmol/kg/min) i.v.; Group 2 (n = 9), 0.8 M NaCl i.c.v. and Ang II i.v.; Group 3 (n = 5), 0.8 M NaCl i.c.v. and Ang II i.v. with daily i.p. injection of guanethidine (40 mg/kg). Significant increase in BP was observed only in Group 2 (from 103 +/- 3 mmHg to 132 +/- 5 mmHg on day 7, p less than 0.001). Addition of i.p. guanethidine to i.c.v. infusion of 0.8 M NaCl and the subpressor dose of Ang II completely prevented increase in the BP, suggesting that the presence of the intact sympathetic nervous system is necessary for the development of BP elevation in response to i.c.v. hypertonic NaCl plus i.v. Ang II. Thus, the sodium status in the central nervous system is important in the regulation of BP and is closely related to the activity of the sympathetic nervous system.     

Disulfide cyclized tripeptide analogues of angiotensin IV as potent and selective inhibitors of insulin-regulated aminopeptidase (IRAP)

The insulin-regulated aminopeptidase (IRAP) localized in areas of the brain associated with memory and learning is emerging as a new promising therapeutic target for the treatment of memory dysfunctions. The angiotensin II metabolite angiotensin IV (Ang IV, Val(1)-Tyr(2)-Ile(3)-His(4)-Pro(5)-Phe(6)) binds with high affinity to IRAP and inhibits this aminopeptidase (K(i) = 62.4 nM). Furthermore, Ang IV has been demonstrated to enhance cognition in animal models and is believed to play an important role in cognitive processes. It is herein reported that displacement of the C-terminal tripeptide His(4)-Pro(5)-Phe(6) with a phenylacetic acid functionality combined with a constrained macrocyclic system in the N-terminal affords potent IRAP inhibitors that are less peptidic in character than the hexapeptide Ang IV. Configurational analysis of three pairs of diastereomeric Ang IV analogues was performed using a combination of solution NMR spectroscopic methods, Monte Carlo conformational searches, and NAMFIS calculations. The compounds encompassing l-amino acids only (4, 8, and 12) showed significantly higher bioactivity compared to their lld-epimers (5, 9, and 13). The best inhibitors in the series, compounds 8 and 12, incorporating a 13- and 14-membered disulfide ring system, respectively, and both with a β(3)-homotyrosine residue (β(3)hTyr) replacing Tyr(2), exhibit K(i) values of 3.3 and 5.2 nM, respectively.     

MIDAZOLAM IS A SAFE AGENT BY COMPARISON WITH THIOPENTONE ON ARRHYTHMIAS IN ISCHAEMIA AND REPERFUSION CONDITIONS IN ISOLATED PERFUSED RAT HEARTS

An involvement of the angiotensin AT₂receptors in some behavioural effects of angiotensin II (Ang II) and its 3–7 fragment [Ang II(3–7)] in rats was studied. To inhibit AT₂receptors we used their selective antagonist CGP 42112A (nicotinic acid-Tyr-N-benzoxyl-carbonyl-Arg-Lys-His-Pro-Ile-OH). Ang II and Ang II(3–7), given intracerebroventricularly (i.c.v.) at the dose of 1 nmol each, significantly enhanced recall of the passive avoidance behaviour and learning of the conditioned avoidance responses (CARs). CGP 42112A (2 μg i.c.v.), inactive on its own in all tests, significantly attenuated facilitation of recall of passive avoidance caused by Ang II and Ang II(3–7). Also, CGP 42112A diminished Ang II improvement of CARs acquisition but not that caused by Ang II(3–7). None of the treatments produced significant anxiolysis in an elevated `plus' maze. Likewise, in an open field no statistically significant differences were recorded except for the abolishment of the Ang II(3–7)-induced increase of rearings and bar approaches by CGP 42112A. It appears that the cognition improving activity of Ang II and Ang II(3–7) is mediated by similar mechanisms and angiotensin AT₂receptors are engaged in these processes.     

Diurnal variation in the effect of angiotensin II on nociception

The aim of this study was to investigate the effect of angiotensin II (Ang II) on nociception at particular time points of a 24-h cycle using different pain stimuli. A parallel investigation of phasic and tonic pain tests revealed different diurnal patterns of pain responses. Phasic pain test (mechanical paw pressure) in rats was characterized with shortest latencies during the dark phase, when the average of motor activity is greatest. Ang II (0.1 microg/animal) increased the latency of pain responses to mechanical and thermal stimulations mainly during the active dark phase. With regard to tonic pain, regardless of a weak circadian fluctuation of the number of pain responses (writhes) in mice, there was a tendency to attenuate the diurnal pattern of nociception. In contrast to the effect of Ang II on the phasic pain, it exerted an antinociceptive effect in the writhing test during the light phase. In summary, Ang II exerted an antinociceptive effect at the time points that have naturally high pain sensitivity.     

The effects of peptide and nonpeptide antagonists of angiotensin II receptors on the level of brain biogenic monoamines in rats with angiotensin II-induced increase of water intake

The effects of peptide and nonpeptide angiotensin II (Ang II)-receptor antagonists (losartan, EXP-3174, saralasin and sarmesin) on the levels of the biogenic monoamines dopamine, noradrenaline and serotonin in the frontal cortex, striatum, hypothalamus and hippocampus of rats with Ang II-induced water intake were investigated. Ang II administered i.c.v. at a dose inducing drinking behavior in rats significantly changed the levels of biogenic monoamines. The latter were also significantly affected by the Ang II-receptor antagonists, as in most cases the drugs antagonized the effect of Ang II. Most pronounced were the effects of Ang II and Ang II-receptor antagonists on the dopamine levels. These levels were reduced to zero after Ang II in all brain structures studied. The drugs tested increased the dopamine levels, restoring their values to the values in vehicle-injected rats. Ang II-receptor antagonists exerted mosaic effects on noradrenaline and 5-HT (serotonin) levels depending on both--the type of biogenic monoamine and the brain structure. There was no relationship between the inhibition of Ang II-induced water intake and the changes in the levels of brain biogenic monoamines under the effect of the Ang II-receptor antagonists. These antagonists may play a role in the modulation of brain monoaminergic neurotransmitter systems.     

Participation of angiotensin receptors in acute hypoxia in mice. II. Effects of angiotensin II nonpeptide receptor ligands losartan (DuP-753) and PD-123319.

The effects of intracerebroventricularly (i.c.v.) administered angiotensin nonpeptide receptor ligands losartan (DuP-753) and PD-123319 and their interactions with Ang II were examined on acute anoxic hypoxia in male mice. Results showed that losartan and PD-123319 exerted antihypoxic effects including increased latency to convulsive seizures and survival time and pretreatment with both drugs enhanced Ang II-increased survival time. Taken together, the results suggest that the antihypoxic effect of losartan and PD-123319 is most likely due to action on brain AT1 and AT2 receptors with both drugs behaving as partial agonists.     

Access of peripherally administered DuP 753 to rat brain angiotensin II receptors.

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.     

Mechanisms of angiotensin II chronotropic effect in anaesthetized dogs.

1. The chronotropic effect of angiotensin II (5 micrograms in 1 ml of Tyrode solution), injected directly into the sinus node artery of 24 anaesthestized and vagotomized dogs pretreated with a beta-adrenoceptor antagonist, was evaluated before and after the administration of: (a) an angiotensin II AT1 receptor antagonist (losartan, 50 micrograms kg-1 min-1 infused i.v. for 120 min), (b) an alpha-adrenoceptor antagonist (prazosin, 1 mg kg-1 i.v. bolus injected), (c) a Ca2+ channel blocker (nifedipine 50, 100 and 200 micrograms kg-1 i.v. bolus injected) and (d) a protein kinase inhibitor (staurosporine, 800 nM infused via the sinus node artery at 0.6 ml min-1 for 15 min). 2. Losartan and staurosporine by themselves had no effect on basal systemic arterial pressure and heart rate, whereas prazosin and nifedipine caused significant diminutions of both parameters. 3. Angiotensin II induced significant increases in heart rate, the mean augmentations being 29 +/- 2 beats min-1. Losartan, nifedipine and staurosporine significantly decreased the chronotropic effect of angiotensin II, the mean respective diminutions being 65 +/- 8, 40 +/- 9 and 64 +/- 10%, whereas prazosin had no effect. 4. This work has demonstrated that angiotensin II exerts in vivo a significant positive chronotropic effect that is mediated via AT1 receptors located in the region of the sinoatrial node. This effect is independent of the adrenergic system. It is decreased by the inhibition of the production of protein kinases, most probably of protein kinase C, and by the blockade of the voltage-sensitive L-type Ca2+ channels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Assessment of brain AT1-receptor on the nocturnal basal and angiotensin-induced thirst and sodium appetite in ovariectomised rats.

OBJECTIVE: Considering the controversial data regarding the role of the brain renin-angiotensin system (RAS) on the thirst and sodium appetite in ovariectomised rats, we aimed to evaluate the role of the brain angiotensin II (Ang II) AT1-receptor on the nocturnal fluids intake. Materials and methods: Groups of Wistar female rats were ovariectomised and chronically given oestrogen or vehicle to evaluate its influence on effects induced by i.c.v. injection of losartan, Ang I and Ang II. RESULTS: The i.c.v. losartan decreased basal water intake in the ovariectomised group. Ang II but not Ang I-induced nocturnal dipsogenic and natriorexigenic responses in ovariectomised rats. In oestrogen-treated rats, both peptides increased fluids intake. Previously, i.c.v. losartan abolished these effects in all groups. Oestrogen replacement decreased the nocturnal fluids intake, attenuated the losartan and Ang II effects, and highlighted the Ang I response. CONCLUSIONS: The present study has shown for the first time the involvement of AT1-receptor in regulating nocturnal basal water and salt intake in ovariectomised rats. In addition, our data have revealed an unexpected increased brain Ang I-mediated fluid intake in oestrogen-treated ovariectomised compared to ovariectomised rats, which was blocked by previous i.c.v. losartan. Our data have therefore shown that oestrogen influences homeostatic behaviours dependent on brain RAS.