angiotensin-iii and ubenimex

The purpose of this investigation was to determine whether the aminopeptidase inhibitor with broad specificity, bestatin, affects angiotensin I (Ang I)-, angiotensin II (Ang II)- or angiotensin III (Ang III)-stimulated collagen gel contraction in cardiac fibroblasts.. Cardiac fibroblasts (from normal male adult rats) were cultured to confluency in Dulbeccos modified Eagles medium (DMEM) with 10% foetal bovine serum (FBS). These fibroblasts (100,000 cells) were then further incubated in a floating collagen gel lattice with the test products Ang I (1 micromol/L), Ang II (100 nmol/L), Ang III (100 nmol/L) and bestatin (100 micromol/L) for three days in DMEM without FBS. The area of the collagen gels embedded with cardiac fibroblasts was determined by a densitometric analysis. Aminopeptidase activity was estimated by spectrophotometric determination of the liberation of p-nitroaniline from alanine- or arginine-p-nitroanilide.. Ang I, II and III stimulated (p<0.05) collagen gel contraction by 30.4+/-4.8 (SEM)%, 27.1+/-3.1% and 15.4+/-3.6% respectively. Ang I- and II-induced stimulation of collagen gel contraction was of the same order but more pronounced (p<0.05) than Ang III- stimulated collagen gel contraction. The Ang I-, II- and III-stimulated collagen contraction was reduced by bestatin. Bestatin, however, did not affect basal collagen gel contraction in cardiac fibroblasts. Bestatin dose-dependently inhibited the hydrolysis of arginine- and alanine-p-nitroanilide in cardiac fibroblasts. When a neutralising antibody to transforming growth factor TGF-b1 was added to the collagen gel simultaneously with the angiotensins, the stimulated collagen contraction was not affected. Beta-aminoproprionitrile, an inhibitor of lysyl oxidase, completely abolished basal as well as Ang I-, II- and III-stimulated collagen contraction in cardiac fibroblasts.. Our data suggest that aminopeptidases are involved in the Ang I-, II- and III-induced stimulation of collagen contraction in cardiac fibroblasts.

Topics: Aminopeptidases; Angiotensin I; Angiotensin II; Angiotensin III; Angiotensins; Anilides; Animals; Cells, Cultured; Collagen; DNA; Fibroblasts; Gels; Hydrolysis; Leucine; Male; Myocardium; Nitro Compounds; Rats; Rats, Wistar; Thymidine

A previous study by our group has demonstrated that the selective AT1-receptor antagonist losartan behaves as a noncompetitive antagonist in rabbit isolated renal artery (RA). In the present investigation, the influence of losartan and irbesartan on the contractile effects of angiotensin II (AII) and its degradation products angiotensin III (AIII) and angiotensin IV (AIV) was determined in the rabbit isolated RA and femoral artery (FA). The arteries were set up in organ chambers and changes in isometric force were recorded. In both rabbit isolated RA and FA preparations, AII, AIII and AIV elicited significant contractile responses with a similar efficacy. These effects were impaired by the presence of functional endothelium in RA preparations but not in FA preparations. In both preparations studied, the effects of AII, AIII and AIV were influenced neither by the aminopeptidase-A and -M inhibitor amastatin (10 microM), nor by the aminopeptidase-B and -M inhibitor bestatin (10 microM). In endothelium-denuded FA preparations, preincubation with losartan (3-300 nM) antagonized AII-, AIII- and AIV-induced contractions in a competitive manner. However, in endothelium-denuded RA preparations, losartan depressed the maximal contractile responses induced by AII but not those induced by AIII and AIV. In the same preparations, preincubation of another selective AT1-receptor antagonist irbesartan (3-30 nM) concentration-dependently shifted AII and AIII curves to the right in an insurmountable manner. The reduction of the maximal response of AII is more potent when compared to that of AIII (47.7 +/- 1.51% vs. 66.7 +/- 1.88%, percentage of the initial maximal response; P < 0.05; n=5). The selective AT2-receptor antagonist PD123177 (1 microM) did not influence the responses to all three peptides in both RA and FA preparations. These heterogeneous antagonistic effects of the two AT1-receptor antagonists studied with respect to the contractile actions of AII, AIII and AIV suggest the possible existence of multiple, functionally relevant AT1-receptor subtypes in rabbit RA preparations.

Topics: Angiotensin II; Angiotensin III; Angiotensin Receptor Antagonists; Animals; Anti-Bacterial Agents; Antihypertensive Agents; Biphenyl Compounds; Endothelium, Vascular; Femoral Artery; Imidazoles; In Vitro Techniques; Irbesartan; Leucine; Losartan; Male; Peptides; Protease Inhibitors; Pyridines; Rabbits; Receptor, Angiotensin, Type 1; Renal Artery; Tetrazoles; Vasoconstrictor Agents

We previously reported that chronic central administration of angiotensin III (AIII) fails to produce sustained drinking behavior in spontaneously hypertensive rats (SHR), possibly because of the development of early desensitization of the angiotensin receptors. The present study extended these findings to the cellular level, using brain-slice preparation from Wistar-Kyoto rats (WKY) and SHR, in conjunction with single-neuron recording in the subfornical organ (SFO), a target site for angiotensin II-induced drinking. We found that a majority of the SFO neurons studied (13/18 in WKY, 20/28 in SHR) responded in a dose-related manner to AIII, given in the range of 10(-6)-10(-5) M. This excitation was receptor-specific, since it was reversed by Ile7-AIII (10(-4)-10(-3) M), the selective AIII antagonist. Bestatin (10(-5)-10(-4) M), an aminopeptidase B inhibitor, did not discernibly affect basal spike frequency when delivered alone. Nevertheless, given in combination with the heptapeptide, bestatin reduced the intensity and duration of SFO neuronal response in WKY to the higher dose (10(-5) M), and in SHR to both doses (10(-6) or 10(-5) M), of AIII. These data suggest that the SFO may also be a central site of action for AIII. Moreover, prolonging the action of AIII by protecting it from being metabolized with bestatin may produce desensitization of the angiotensin receptors on SFO neurons. This was particularly so in the SHR, which are thought to be defective in the degradation of the heptapeptide in the brain.

Topics: Aminopeptidases; Angiotensin III; Angiotensin Receptor Antagonists; Animals; Dose-Response Relationship, Drug; In Vitro Techniques; Leucine; Male; Neurons; Prosencephalon; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Angiotensin; Subfornical Organ

Microinjection of angiotensin II and III into the rostral ventrolateral medulla of anesthetized barodenervated rabbits elicited in both cases pressor responses, which were of similar magnitude and time course. The responses to angiotensin II and III were either unchanged or increased in the presence of compounds which inhibit their degradation to shorter length peptides. The results indicate that both angiotensin peptides are independently capable of eliciting pressor responses in the rostral ventrolateral medulla.

Topics: Angiotensin II; Angiotensin III; Animals; Anti-Bacterial Agents; Blood Pressure; Histocytochemistry; Horseradish Peroxidase; Leucine; Medulla Oblongata; Microinjections; Oligopeptides; Peptides; Rabbits; Sodium; Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; Wheat Germ Agglutinins

A soluble tripeptidylaminopeptidase has been isolated from human post-mortem cerebral cortex by anion exchange, hydrophobic interaction and size-exclusion chromatography. From gel filtration studies the active enzyme can exist in both high molecular weight (M(r) > 10(6) and smaller forms. The enzyme hydrolyses Ala-Ala-Phe-7-amido-4-methylcoumarin with a pH optimum of around 7.5 and Km of 148 microM. It did not hydrolyse N-succinyl-Ala-Ala-Phe-7-amido-4-methylcoumarin, aminoacyl- or dipeptidyl-7-amido-methylcoumarins and was not inhibited by bestatin. The enzyme was inhibited by phenylmethylsulphonyl-fluoride, 3,4-dichloroisocoumarin, N-hydroxymercuriphenyl-sulphonic acid and N-ethylmaleimide showing that its activity is serine and cysteine dependent. The purified enzyme released tripeptides from several naturally occurring neuropeptides with quite broad specificity. Cholecystokinin octapeptide, angiotensin III and neurokinin A were the most rapidly hydrolysed. Peptides with Pro residues around the point of cleavage were not hydrolysed.

Topics: Amino Acid Sequence; Aminopeptidases; Angiotensin III; Cerebral Cortex; Chromatography; Chromatography, Gel; Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; Humans; Hydrogen-Ion Concentration; Leucine; Molecular Sequence Data; Molecular Weight; Neurokinin A; Neuropeptides; Serine Endopeptidases; Sincalide; Substrate Specificity

We evaluated the chronic effect of angiotensin-III (AIII) in the promotion of drinking behavior in spontaneously hypertensive (SH) and normotensive Wistar-Kyoto (WKY) rats, using conscious, freely moving, male, adult animals that had been instrumented with an intracerebroventricular (icv) cannula connected to an osmotic mini-pump for 7-day infusion. Chronic icv infusion of AIII (5 or 10 pmol/min) elicited robust, dose-dependent, and Ile7-AIII (100 pmol/min; as specific antagonist)-reversible dipsogenesis in both SH and WKY rats, with higher water intake in the former strain. However, the drinking response in the SHRs exhibited a sharp drop after 3 days of AIII infusion, during which acute AIII (80 pmol, icv) challenges also failed to induce dipsogenesis. Chronic icv infusion of bestatin (150 pmol/min), an aminopeptidase-B inhibitor, did not by itself discernibly affect basal drinking. When combined with AIII (5 or 10 pmol/min), however, bestatin, respectively, suppressed and augmented the dipsogenic response of SH and WKY rats to the heptapeptide. These results suggest that chronic administration of AIII did not produce sustained drinking behavior in SHRs, possibly because of the development of early desensitization of the angiotensin receptors.

Topics: Aminopeptidases; Angiotensin III; Animals; Carbachol; Cerebral Ventricles; Drinking; Hypertension; Leucine; Male; Rats; Rats, Inbred SHR; Rats, Inbred WKY

In homogenates of the endothelium and smooth muscle cum adventitia of the rat aorta, exogenous angiotensin (ANG) I was found to be degraded to des-aspartate-ANG I (des-Asp-ANG I) instead of ANG II. ANG II and ANG III were not detectable in either of the homogenates after 5, 10 and 30 min of incubation with the decapeptide. However, both the homogenates were able to catalyse hippuryl-L-histidyl-L-leucine (HHL) to hippuric acid and the catalysis was completely inhibited by 3 microM captopril. The data show that the angiotensin converting enzyme (ACE) present in the homogenates of rat aorta, prepared by normal laboratory procedures, is not able to hydrolyse ANG I to ANG II. This finding has important consequences in the study of vascular ACE as the assay of the enzyme is often carried out using crude homogenate and HHL or other artificial substrates. In addition, the aminopeptidase that degraded ANG I to des-Asp-ANG I was not inhibited by either amastatin or bestatin, indicating that it was not aminopeptidase A or B. Together with the recent findings of other investigators which show that the de novo production of ANG II in vascular tissues is stimulated and inhibited by beta- and alpha-agonists, respectively, our present data may suggest that production of vascular ANG II occurs only in intact tissues and is probably under adrenergic regulation.

Topics: Amino Acid Sequence; Aminopeptidases; Angiotensin I; Angiotensin II; Angiotensin III; Animals; Anti-Bacterial Agents; Aorta; Endothelium, Vascular; Leucine; Male; Molecular Sequence Data; Muscle, Smooth, Vascular; Oligopeptides; Peptides; Rats; Rats, Sprague-Dawley

1. Experiments were performed with peptidase inhibitors on rabbit aortic strip preparations, to determine whether endogenous peptidase activity can influence the potency estimates for angiotensin receptor agonists and antagonists in this tissue. 2. Angiotensin II (A II) and angiotensin III (A III) both induced concentration-related contractions of rabbit aortic strip preparations. A III was approximately 38 fold less potent than A II, and the gradient of the A III concentration-response curve (1.00 +/- 0.04) was significantly more shallow than that (1.76 +/- 0.05) of the A II curve. 3. Neither the aminopeptidase-A and -M inhibitor, amastatin, nor the aminopeptidase-B and -M inhibitor, bestatin, affected the potency of, or the maximum response to, A II. In contrast, the potency of A III was increased by both amastatin and bestatin. Amastatin had the most marked effect and at 10 microM caused approximately a 12 fold increase in the potency of A III (EC50 values, 102 nM and 8.6 nM in the absence and presence of amastatin, respectively), and also significantly steepened the gradient of the A III concentration-response curve. Amastatin did not affect the position or shape of the concentration-response curve to the alpha 1-adrenoceptor agonist, phenylephrine. Finally, the carboxypeptidase-N inhibitor, D-L-mercaptomethyl-3-guanidine-ethylpropanoic acid (MERGETPA) did not change the position or shape of the concentration-response curves to either A II or A III.4. In the presence of amastatin, the potency of the peptide angiotensin receptor antagonist, Ile7-A III (100nM-l microM ), was increased approximately 13 fold (pA2, with A II as the agonist, 7.0 +/- 0.1 and 8.1 +/- 0.1, in the absence and presence of amastatin, respectively). However, the potency of the nonpeptide angiotensin receptor antagonist, DuP 753 (30-300 nM), was little affected by amastatin (pA2, 8.2 +/- 0.1 and 8.1 +/- 0.1 in the absence and presence of amastatin, respectively).5. The results of this study suggest that endogenous aminopeptidase activity in the rabbit thoracic aorta can profoundly affect estimates of the potency of peptide angiotensin receptor agonists and antagonists.A suitable aminopeptidase inhibitor should therefore be included in studies, using this tissue, which aim to classify angiotensin receptor subtype(s) based on the rank order of peptide angiotensin receptor agonist and/or antagonist potencies.

Topics: 3-Mercaptopropionic Acid; Adrenergic alpha-Agonists; Amino Acid Sequence; Aminopeptidases; Angiotensin II; Angiotensin III; Animals; Anti-Bacterial Agents; Aorta, Thoracic; Dose-Response Relationship, Drug; In Vitro Techniques; Leucine; Male; Molecular Sequence Data; Muscle Contraction; Oligopeptides; Peptides; Phenylephrine; Rabbits; Receptors, Angiotensin; Vasoconstriction

We evaluated the possible interactions between central alpha 2-adrenoceptors and endogenous angiotensin III (AIII) in Sprague-Dawley rats anesthetized with pentobarbital sodium (50 mg/kg, i.p.). The cardiovascular suppressive effects of the alpha 2-adrenoceptor agonist, guanabenz, were used as our experimental index for alpha 2-adrenoceptor activity. Intracerebroventricular (i.c.v.) administration of AIII (100 or 200 pmol) attenuated the hypotensive and negative inotropic and chronotropic actions of guanabenz (100 micrograms/kg, i.v.). Blocking the endogenous activity of the heptapeptide with its specific antagonist, Ile7-AIII (50 or 100 nmol, i.c.v.), on the other hand, potentiated the circulatory inhibitory efficacy of the aminoguanidine compound. These modulatory effects were essentially duplicated by bilateral microinjection of AIII (20 or 40 pmol) or Ile7-AIII (10 or 20 nmol) into the nucleus reticularis gigantocellularis (NRGC), a medullary site that is critically involved in the cardiovascular suppressive actions of guanabenz. I.c.v. injection of bestatin (200 nmol) also reduced the circulatory depressive potency of guanabenz. This effect was respectively enhanced and reduced when the aminopeptidase inhibitor was given simultaneously with AIII (200 pmol) and Ile7-AIII (100 nmol). These results suggest that the endogenous AIII may exert a tonic inhibition on the alpha 2-adrenoceptors in in the NRGC that are involved in cardiovascular regulation.

Topics: Angiotensin III; Animals; Brain; GTP-Binding Proteins; Guanabenz; Hemodynamics; Injections, Intraventricular; Leucine; Male; Rats; Rats, Inbred Strains; Receptors, Adrenergic, alpha

Rats received the aminopeptidase inhibitors amastatin (AM) and bestatin (BE), and carboxypeptidase inhibitor Plummer's (PL) via intracerebroventricular infusion in various combinations, i.e. PL alone, AM + BE, and a cocktail consisting of AM + BE + PL. Blood pressure responses were recorded and a postinfusion sample of cerebrospinal fluid (CSF) was radioimmunoassayed for endogenous angiotensin levels. Results indicate that CSF angiotensin was increased approximately 1.5x over control levels when PL was infused; a 2.5x increase accompanied AM + BE administration; and a 10.3x elevation was measured when all 3 inhibitors were infused as a cocktail. Concomitant elevations in blood pressure accompanied increased concentrations of angiotensin. We conclude that endogenous levels of angiotensin can be significantly increased in the ventricular space when a combination of these inhibitors is utilized to protect both the amino and carboxyl terminals of the angiotensin molecule from enzymatic degradation.

Topics: 3-Mercaptopropionic Acid; Angiotensin II; Angiotensin III; Animals; Anti-Bacterial Agents; Blood Pressure; Carboxypeptidases; Cerebral Ventricles; Injections, Intraventricular; Leucine; Male; Oligopeptides; Peptides; Protease Inhibitors; Radioimmunoassay; Rats; Rats, Inbred Strains

Two D-amino acid substitution angiotensin analogues were compared against native angiotensin II (AII) and angiotensin III (AIII) for their resistance to brain tissue-induced degradation and for pressor potency when intracerebroventricularly (i.c.v.) infused in Sprague-Dawley rats. The in vitro results indicate that [D-Asp1]AII was very resistant to degradation, AII and [D-Arg1]AIII were degraded at similar rates, while AIII was the most rapidly degraded. In vivo results revealed that AII, AIII and [D-Arg1]AIII produced greater pressor responses than [D-Asp1]AII. Intracerebroventricular pretreatment with the aminopeptidase A inhibitor, amastatin, significantly reduced the subsequent pressor response to i.c.v. infused [D-Asp1]AII presumably by inhibiting its conversion to AIII. In contrast, pretreatment with the aminopeptidase B inhibitor, bestatin, potentiated the subsequent pressor response to i.c.v. infused [D-Arg1]AIII, presumably by inhibiting the conversion of [D-Arg1]AIII to the less active hexapeptide AII(3-8). Next, i.c.v. pretreatment with the specific angiotensin receptor antagonist, [Sar1, Thr8]AII (Sarthran) was found to greatly diminish the subsequent pressor responses to i.c.v. infused [D-Asp1]AII and [D-Arg1]AIII, suggesting that these analogues are having their effect at the same brain angiotensin receptor site. These results support the hypothesis that AIII, or AIII-like ligands, may serve as the active form of brain angiotensin.

Topics: Aminopeptidases; Angiotensin II; Angiotensin III; Animals; Anti-Bacterial Agents; Blood Pressure; Dose-Response Relationship, Drug; Enzyme Inhibitors; Injections, Intraventricular; Leucine; Male; Oligopeptides; Peptides; Rats; Rats, Inbred Strains

Recent iontophoretic data suggest that conversion of angiotensin II (AII) to angiotensin III (AIII) may be necessary before the peptide can activate central angiotensin-sensitive neurons. Furthermore, this conversion may be inhibited by the aminopeptidase A inhibitor, amastatin. In the present study we investigated the importance of aminopeptidase activity on central angiotensin-induced pressor responses. Intracerebroventricular (i.c.v.) pretreatment with amastatin, suppressed i.c.v. AII-induced pressor responses. Pretreatment with the aminopeptidase B inhibitor, bestatin, increased pressor responses to AIII. Pressor responses induced by the aminopeptidase-resistant analogue, [Sar1]angiotensin II, were not affected by pretreatment with angiotensin inhibitors. These results support the hypothesis that AII must be converted to AIII to be active in the brain.

Topics: Aminopeptidases; Angiotensin II; Angiotensin III; Animals; Anti-Bacterial Agents; Blood Pressure; Cerebral Ventricles; Injections, Intraventricular; Leucine; Male; Oligopeptides; Peptides; Rats; Rats, Inbred Strains; Reference Values

Improved immunohistochemical and quantitative microiontophoretic methods were used to characterise angiotensinergic and angiotensin-sensitive neurones in the paraventricular nucleus (PVN) of the rat. The results can be summarised as follows: 1) Angiotensinogen was found in PVN neurones, astrocytes in the diencephalon which make putative contacts with microvessels, and in cells of the choroid plexus. 2) Affinity-purified angiotensin II/III antibodies were used to locate immunoreactive AII/III in large PVN neurones and their fibre tracts which project either caudally or ventrally to the neurohypophysis. 3) Quantitative microiontophoretic studies showed that PVN neurones are more sensitive to angiotensin II than to angiotensin II. 4) Iontophoretic co-application of the selective aminopeptidase inhibitors bestatin and amastatin, together with angiotensin II and angiotensin III produced results consistent with a central role for angiotensin III.

Topics: Aminopeptidases; Angiotensin II; Angiotensin III; Animals; Anti-Bacterial Agents; Immunohistochemistry; Iontophoresis; Leucine; Male; Oligopeptides; Paraventricular Hypothalamic Nucleus; Peptides; Rats; Rats, Inbred SHR; Rats, Inbred Strains; Rats, Inbred WKY

The metabolism of [125I]angiotensin II (AII, octopeptide) and [125I]angiotensin III (AIII, heptapeptide) was determined in the cerebroventricular compartment following intracerebroventricular (i.c.v.) pretreatment with artificial cerebrospinal fluid (aCSF) or the aminopeptidase B inhibitor, bestatin (BE). Microwave fixation was used to stop brain aminopeptidase activity followed by high-performance liquid chromatography methods to measure degradation. The resulting mean t 1/2 values were: aCSF/AII = 23.5 s, BE/AII = 32.0 s; aCSF/AIII = 8.2 s, BE/AIII = 16.0 s. A second experiment indicated that i.c.v. administered BE induced considerable water consumption, while amastatin (AM, an aminopeptidase A inhibitor) did not. Combined i.c.v. treatment with BE/AII or BE/AIII produced water consumptions that were equivalent with the sum of the water intakes due to independent treatments. Unexpectedly, combined treatment with AM/AII also significantly facilitated water consumption as compared with the independent treatments. These results suggest that i.c.v. BE-induced drinking is due to the extension of the half-life of endogenous AIII, and that both AM and BE facilitate drinking to i.c.v. AII and AIII by inhibiting the degradation of AII and AIII. This delay in degradation prolongs the action of AIII at central angiotensin receptors while also slowing the conversion of AII to AIII, thus providing a depot of available AII to be converted to AIII in an obligatory manner.

Topics: Aminopeptidases; Angiotensin II; Angiotensin III; Animals; Brain; Cerebral Ventricles; Drinking Behavior; Injections, Intraventricular; Kinetics; Leucine; Male; Microwaves; Rats; Rats, Inbred Strains

We evaluated the participation of endogenous brain angiotensin III (AIII) in central cardiovascular regulation, using the intracerebroventricular injection technique in Sprague-Dawley rats anesthetized with pentobarbital sodium (50 mg/kg, i.p.). AIII (100 pmol) promoted an elevation in systemic arterial pressure and a reduction in the baroreceptor reflex (BRR) response. Its specific antagonist, Ile7-AIII (100 nmol), and the aminopeptidase inhibitor, bestatin (200 nmol), on the other hand, augmented the response of the same reflex. The suppressive action of AIII (100 pmol) on the BRR was attenuated, and the enhancing effect of Ile7-AIII (100 nmol) was potentiated, however, when these two peptides were administered simultaneously with bestatin (200 nmol). All these events were significantly different from their controls during the first 10-15 min following injection, parallel to the time course of a discernible action of AIII on systemic arterial pressure. We discussed that the endogenous AIII in the central nervous system may participate in cardiovascular control by tonically inhibiting the BRR, in concert with other brain neuropeptides.

Topics: Angiotensin II; Angiotensin III; Animals; Blood Pressure; Cardiovascular Physiological Phenomena; Cardiovascular System; Injections, Intraventricular; Leucine; Male; Phenylephrine; Pressoreceptors; Rats; Rats, Inbred Strains; Time Factors

In the metabolism of angiotensin peptides by tissue angiotensinases, aminopeptidases A, B, M and leucine aminopeptidase have been identified as being particularly effective. Because the inhibitory actions of amastatin (AM) and bestatin (BE) are relatively specific for these aminopeptidases, we have examined the effects of these inhibitors on the binding, degradation and pressor activity of angiotensin II (AII) and angiotensin III (AIII). Within 30 min at 37 degrees C, significant metabolism of 125I-AII and 125I-AIII by homogenates of a block of tissue containing hypothalamus, thalamus, septum and anteroventral third ventricle regions of the brain was observed. A majority of 125I-AIII metabolism was due to soluble peptidases, whereas that of 125I-AII primarily resulted from membrane-bound peptidases. AM, BE and reduced incubation temperatures significantly decreased the metabolism of 125I-AII and 125I-AIII. After appropriate adjustments to reflect the proportion of intact radioligand bound, temperature- or inhibitor-induced decreases in metabolism were matched by corresponding increases in specific binding. Heat-treated bovine serum albumin, as a nonspecific peptidase inhibitor, had no effect on either the metabolism or binding of the ligands used. In accordance with their actions in vitro, i.c.v. administration of AM and BE prolonged the pressor activity of subsequently applied AII and AIII. Unexpectedly, the amplitude of the pressor response to AIII was increased by BE, whereas that to AII was decreased by AM. The results of this study indicate that the metabolism of AII and AIII by aminopeptidases is relatively specific and acts to modulate the actions of these peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Aminopeptidases; Angiotensin II; Angiotensin III; Animals; Anti-Bacterial Agents; Blood Pressure; Iodine Radioisotopes; Leucine; Male; Oligopeptides; Peptides; Rats; Rats, Inbred Strains

The effect of acute intracerebroventricular (i.c.v.) injections of angiotensin II and III (ANG II and ANG III; 0, 1, 10 and 100 pmol in 2 microliters artificial cerebrospinal fluid (CSF) on blood pressure and water consumption was investigated in Okamoto-Aoki spontaneously hypertensive rats (SHR), and Wistar-Kyoto (WKY) and Sprague-Dawley (SD) normotensive controls. Heightened sensitivity to i.c.v. ANG II and ANG III was observed in the SHR compared with the WKY and SD strains (P less than 0.001), for both pressor and drinking responses. In addition, i.c.v. treatment with an aminopeptidase B inhibitor, bestatin (20 nmol in 1 microliter artificial CSF) significantly potentiated the heightened pressor response to i.c.v.-injected ANG II and ANG III (100 pmol) in SHR and to a lesser degree in WKY animals compared with SD controls (P less than 0.001). These results suggest that a dysfunction in central aminopeptidase activity results in an extended life of endogenous angiotensins, and perhaps other peptides that may contribute to the high blood pressure seen in this animal model of human essential hypertension.

Topics: Angiotensin II; Angiotensin III; Animals; Blood Pressure; Cerebral Ventricles; Drinking; Hypertension; Injections, Intraventricular; Leucine; Male; Rats; Rats, Inbred SHR; Rats, Inbred Strains; Rats, Inbred WKY; Thirst

Alert spontaneously hypertensive (SH) rats, prepared with indwelling carotid artery catheters, demonstrated heightened and prolonged blood pressure (BP) responses to intracerebroventricular (i.c.v.) injections of 10 and 100 pmol angiotensin II and III (AII and AIII) as compared with Wistar-Kyoto (WKY) and Sprague-Dawley normotensive animals. Pretreatment with the aminopeptidase B inhibitor bestatin (10 nmol, i.c.v.) potentiated and prolonged the heightened pressor response to AIII (100 pmol, i.c.v.) in SH rats. These results suggest that dysfunction of angiotensin peptidase activity may be contributing to the progressive and sustained elevations in blood pressure noted to occur in the SH rat model of human essential hypertension.

Topics: Angiotensin II; Angiotensin III; Animals; Blood Pressure; Brain; Endopeptidases; Hypertension; Leucine; Male; Rats; Rats, Inbred SHR; Rats, Inbred Strains; Rats, Inbred WKY