RESUMO
The aim of this work was to evaluate the potential of liposomes as a tool for the sustained release of the short half-life peptides of the renin-angiotensin system in a specific site of the brain. Angiotensin (Ang)-(1-7) was selected for this study because of its known cardiovascular effects at the level of the rostral ventrolateral medulla (RVLM) and because of the considerable interests in elucidating its physiopathological role as a neuromodulator. Ang-(1-7)-containing liposomes (LAng) were microinjected unilaterally in the RVLM of Wistar rats, and the effects on blood pressure (MAP) and heart rate were evaluated by telemetry. Empty liposomes (Lemp) were used as control. LAng elicited a significant pressor effect during daytime and bradycardia during nighttime that lasted for 5 and 3 days, respectively. These cardiovascular effects resulted in a significant attenuation of the circadian variations of MAP and heart rate. In the case of MAP, a significant inversion of the circadian rhythm was observed on day 2 after LAng microinjection. None of these effects were observed following microinjection of Lemp. Using this novel technique, it was possible to establish, in chronic conditions, the pressor effect of Ang-(1-7) at the RVLM. Moreover, our data unmasks a new physiological role for Ang-(1-7) at the level of the RVLM: modulation of the circadian rhythms of MAP and heart rate.
Assuntos
Angiotensina I/administração & dosagem , Pressão Sanguínea/efeitos dos fármacos , Frequência Cardíaca/efeitos dos fármacos , Bulbo/efeitos dos fármacos , Fragmentos de Peptídeos/administração & dosagem , Angiotensina I/fisiologia , Animais , Ritmo Circadiano/efeitos dos fármacos , Ritmo Circadiano/fisiologia , Preparações de Ação Retardada , Lipossomos , Masculino , Fragmentos de Peptídeos/fisiologia , Ratos , Ratos WistarRESUMO
We have previously demonstrated that microinjections of the selective angiotensin-(1-7) [ANG-(1-7)] antagonist, A-779, into the rostral ventrolateral medulla (RVLM) produces a significant fall in mean arterial pressure (MAP) and heart rate (HR) in both anesthetized and conscious rats. In contrast, microinjection of angiotensin II (ANG II) AT(1) receptor antagonists did not change MAP in anesthetized rats and produced dose-dependent increases in MAP when microinjected into the RVLM of conscious rats. In the present study, we evaluated whether endogenous ANG-(1-7) and ANG II acting at the RVLM contribute to the hypertension of transgenic rats harboring the mouse renin Ren-2 gene, TGR(mREN2)27. Unilateral microinjection of A-779 (0.1 nmol) produced a significant fall in MAP (-25 +/- 5 mmHg) and HR (-57 +/- 20 beats/min) of awake TGR rats. The hypotensive effect was greater than that observed in Sprague-Dawley (SD) rats (-9 +/- 2 mmHg). Microinjection of the AT(1) antagonist CV-11974 (0.2 nmol) produced a fall in MAP in TGR rats (-14 +/- 4 mmHg), contrasting with the pressor effect observed in SD rats (33 +/- 9 mmHg). These results indicate that endogenous ANG-(1-7) exerts a significant pressor action in the RVLM, contributing to the hypertension of TGR(mREN2)27 transgenic rats. The role of ANG II at the RVLM seems to be dependent on its endogenous level in this area.
Assuntos
Angiotensina II/análogos & derivados , Angiotensina II/metabolismo , Angiotensina I/metabolismo , Hipertensão/metabolismo , Bulbo/metabolismo , Fragmentos de Peptídeos/metabolismo , Renina/genética , Angiotensina I/administração & dosagem , Angiotensina II/administração & dosagem , Antagonistas de Receptores de Angiotensina , Animais , Animais Geneticamente Modificados , Anti-Hipertensivos/administração & dosagem , Benzimidazóis/administração & dosagem , Compostos de Bifenilo , Pressão Sanguínea/efeitos dos fármacos , Pressão Sanguínea/genética , Frequência Cardíaca/efeitos dos fármacos , Hipertensão/genética , Masculino , Bulbo/efeitos dos fármacos , Microinjeções , Fragmentos de Peptídeos/administração & dosagem , Ratos , Ratos Sprague-Dawley , Tetrazóis/administração & dosagemRESUMO
OBJECTIVES: In the present study, we evaluated the effect of angiotensin-(1-7) [Ang-(1-7)] and its selective antagonist, D-Ala7-Ang-(1-7) (A-779), at the nucleus tractus solitarii (nTS), in the modulation of the bradycardic component of the baroreceptor reflex. METHODS: Mean arterial pressure (MAP) and heart rate were continuously recorded. Reflex changes in heart rate elicited by bolus injection of graded doses of phenylephrine were evaluated before and after bilateral microinjection (glass micropipette) of Ang-(1-7) (10 pmol or 25 pmol), A-779 (50 pmol) or saline (vehicle) into the nTS of urethane anesthetized male Wistar rats or spontaneously hypertensive rats (SHR). The averaged ratio between reflex changes in heart rate and changes in MAP was used as index of baroreflex sensitivity. RESULTS: Microinjection of Ang-(1-7) into the nTS elicited significant decreases in MAP and heart rate in both Wistar and SHR. While the decrease in MAP was similar in both strains, the changes in heart rate were smaller in SHR. A-779 produced small changes in MAP and heart rate that were no different from those induced by saline. After microinjection of 10 pmol of Ang-(1-7) into the nTS of normotensive rats, there was a significant increase in baroreflex sensitivity. In SHR, only the microinjection of a higher dose (25 pmol) of Ang-(1-7) produced a significant increase in baroreflex sensitivity. A significant reduction inbaroreflex sensitivity was observed after microinjection of A-779 (50 pmol) in both strains. CONCLUSIONS: These results indicate that Ang-(1-7) exerts a tonic modulatory effect on the baroreflex control of heart rate at the nTS, probably through a non-AT1 non-AT2 receptor subtype. In addition, our data showed a reduced sensitivity to Ang-(1-7) at the nTS of SHR, that could be accounting, at least in part, for the decreased baroreflex sensitivity present in this model of hypertension.
Assuntos
Angiotensina II/análogos & derivados , Angiotensina I/farmacologia , Barorreflexo/efeitos dos fármacos , Barorreflexo/fisiologia , Frequência Cardíaca/efeitos dos fármacos , Frequência Cardíaca/fisiologia , Hipertensão/fisiopatologia , Fragmentos de Peptídeos/farmacologia , Núcleo Solitário/efeitos dos fármacos , Núcleo Solitário/fisiologia , Angiotensina I/administração & dosagem , Angiotensina I/antagonistas & inibidores , Angiotensina II/farmacologia , Animais , Pressão Sanguínea/efeitos dos fármacos , Pressão Sanguínea/fisiologia , Masculino , Microinjeções , Fragmentos de Peptídeos/administração & dosagem , Fragmentos de Peptídeos/antagonistas & inibidores , Ratos , Ratos Endogâmicos SHR , Ratos Wistar , Receptores de Angiotensina/efeitos dos fármacos , Núcleo Solitário/anatomia & histologiaRESUMO
In this study, we characterized the cardiovascular effects produced by microinjection of doses in the femtomole range of bradykinin (BK) into the nucleus tractus solitarii of male Wistar rats (230-280 g, n = 120) anesthetized with urethane (1.2 g/kg, i.p.). Microinjections of BK (1, 10, 100 fmol, and 1 and 10 pmol, in 50 nl) or vehicle (NaCl, 0.9%) were made by using a triple-barreled glass micropipette into the medial nTS (0.4 mm anterior, 0.3 mm lateral to the obex and 0.3 mm deep from the dorsal surface). Microinjection of BK produced a shallow dose-dependent decrease in mean arterial pressure and heart rate reaching -18 +/- 6 mmHg and -21 +/- 5 beats/min, with the dose of 10 pmol. The peripheral mechanism of these effects, tested in animals treated with methylatropine (2 mg/kg, i.v.), or propranolol (2 mg/kg, i.v.) or prazosin (30 micrograms/kg, i.v.), was shown to be mainly dependent on an increase in vagal efferent activity for bradycardia and a decrease in sympathetic activity for hypotension. In order to investigate the receptor subtype involved in these effects, BK was microinjected into the nTS before and after the injection of the B1 receptor antagonist, Des-Arg9-Leu8-BK (DALBK) (11.5 pmol) or before and after the B2 receptor antagonist, HOE-140 (7.7 pmol). The cardiovascular effects of BK were significantly attenuated by the microinjection of HOE-140 and DALBK into the nTS. The effect of BK microinjected into the nTS on the baroreflex modulation was also investigated. While BK produced a significant facilitation of the baroreflex, HOE-140 and DALBK produced a significant attenuation of the baroreceptor control of heart rate. Taken together, the data presented in this study indicate the nTS as a site, in the central nervous system, for the modulatory effect of BK on the central cardiovascular control.
Assuntos
Bradicinina/farmacologia , Hemodinâmica/efeitos dos fármacos , Núcleo Solitário/fisiologia , Anestesia , Animais , Barorreflexo/efeitos dos fármacos , Pressão Sanguínea/efeitos dos fármacos , Bradicinina/administração & dosagem , Antagonistas dos Receptores da Bradicinina , Relação Dose-Resposta a Droga , Frequência Cardíaca/efeitos dos fármacos , Masculino , Microinjeções , Nervos Periféricos/efeitos dos fármacos , Pressorreceptores/efeitos dos fármacos , Ratos , Ratos Wistar , Receptores da Bradicinina/efeitos dos fármacosRESUMO
In this study we describe a new angiotensin antagonist [Asp1-Arg2-Val3-Tyr4-Ile5-His6-D-Ala7, (A-779)] selective for the heptapeptide angiotensin-(1-7) [Ang-(1-7)]. A-779 blocked the antidiuretic effect of Ang-(1-7) in water-loaded rats and the changes in blood pressure produced by Ang-(1-7) microinjection into the dorsal-medial and ventrolateral medulla. In contrast, A-779 did not change the dipsogenic, pressor, or myotropic effects of angiotensin II (Ang II). Also, A-779 did not affect the antidiuretic effect of vasopressin or the contractile effects of angiotensin III, bradykinin, or substance P on the rat ileum. In the rostral ventrolateral medulla, the pressor effect produced by Ang-(1-7) microinjection was completely blocked by A-779 but not by AT1 or AT2 receptor antagonists (DUP 753 and CGP 42112A, respectively). Conversely, the pressor effect produced by Ang II was not changed by A-779 but was completely blocked by DUP 753. Binding studies substantiated these observations: A-779 did not compete significantly for 125I-Ang II binding to adrenocortical membranes at up to a 1 microM concentration. Low affinity binding was also observed in adrenomedullary membranes with an IC50 greater than 10 microM. Our results show that A-779 is a potent and selective antagonist for Ang-(1-7). More importantly, our data indicate that specific angiotensin receptors mediate the central and peripheral actions of Ang-(1-7).