Influência do exercício aeróbio na renina de portadores de hipertensão arterial com sobrepeso

FUNDAMENTO: A atividade do sistema renina-angiotensina-aldosterona tem relação direta com sobrepeso e sedentarismo, e essas variáveis se associam à hipertensão arterial (HA). O exercício aeróbio propicia melhor controle da pressão arterial (PA) por agir nos mecanismos da regulação pressórica, dentre eles, a atividade de renina plasmática (ARP). OBJETIVO: Avaliar a influência do exercício aeróbio sobre ARP em portadores de HA com sobrepeso. MÉTODOS: Foram avaliados níveis pressóricos, bioquímicos e antropométricos pré e pós-treinamento de 16 semanas, três vezes por semana, a 60%-80% da frequência cardíaca máxima. Os dados foram expressos em média ± desvio padrão ou mediana e intervalo interquartílico, e analisados pelo teste t, Mann-Withney e ANOVA (p < 0,05). RESULTADOS: Vinte indivíduos apresentaram média de idade de 57 ± 7,0 anos e índice de massa corpórea de 30 ± 3,5 kg/m². O treinamento aeróbio promoveu a redução da porcentagem de gordura corporal (35 ± 7,8 para 30 ± 5,6 %), da frequência cardíaca (FC) (80 ± 10,4 para 77 ± 8,5 bpm) e da pressão de pulso (PP) (50 ± 11,8 para 46 ± 10,0 mmHg) na amostra geral (p < 0,05), sem redução da ARP, que variou de 0,8 (0,45-2,0) a 1,45 (0,8-2,15) ηg/ml/h (p = 0,055). No grupo com redução da circunferência abdominal (CA) (n = 8) houve redução da PA sistólica e PP (p < 0,05). No grupo sem redução da CA, nenhuma das variáveis pressóricas apresentou alteração. A ARP não se associou com nenhuma variável estudada. O efeito do treinamento aeróbio associou-se à redução da PP na casuística total e à redução da PA sistólica no subgrupo com redução da CA. CONCLUSÃO: O treinamento aeróbio não reduziu a ARP em hipertensos com sobrepeso.

Commissural nucleus of the solitary tract is important for cardiovascular responses to caudal pressor area activation

The nucleus of the solitary tract (NTS) is the site of the first synapse of cardiovascular afferent fibers in the central nervous system. Important mechanisms for cardiovascular regulation are also present in the caudal pressor area (CPA) localized at the caudal end of the ventrolateral medulla. In the present study we sought to investigate the role of the commissural subnucleus of the NTS (commNTS) on pressor and tachycardic responses induced by L-glutamate injected into the CPA. Male Holtzman rats (n=8 rats/group) anesthetized with urethane (1.2 g/kg of body weight, iv) received injections of the GABAA receptor agonist muscimol into the commNTS. Unilateral injection of L-glutamate (10 nmol/ 100 nL) into the CPA increased mean arterial pressure (MAP, 31 4 mm Hg, vs. saline: 3 +/- 2 mm Hg) and heart rate (HR, 44 8 bpm, vs. saline: 10 7 bpm). inhibition of commNTS neurons with muscimol (120 pmol/60 nL) abolished the increase in MAP (9 4 mm Hg) and HR (17 7 bpm) produced by L-glutamate into the CPA. The present results suggest that the pressor and tachycardic responses to CPA activation are dependent on commNTS mechanisms.

Cardiovascular responses to microinjection of L-glutamate into the NTS in AV3V-lesioned rats

The excitatory amino acid L-glutamate injected into the nucleus of the solitary tract (NTS) in unanesthetized rats similar to peripheral chemoreceptor activation increases mean arterial pressure (MAP) and reduces heart rate. In this study, we investigated the effects of acute (I day) and chronic (15 days) electrolytic lesions of the preoptic-periventricular tissue surrounding the anteroventral third ventricle (AV3V region) on the pressor and bradycardic responses induced by injections of L-glutamate into the NTS or peripheral chemoreceptor activation in unanesthetized rats. Male Holtzman rats with sham or electrolytic AV3V lesions and a stainless steel cannula implanted into the NTS were used. Differently from the pressor responses (28 +/- 3 mm Hg) produced by injections into the NTS of sham-lesioned rats, L-glutamate (5 nmol/ 100 nl) injected into the NTS reduced MAP (-26 +/- 8 mm Hg) or produced no effect (2 7 turn Hg) in acute and chronic AV3V-lesioned rats, respectively. The bradycardia to L-glutamate into the NTS and the cardiovascular responses to chemoreflex activation with intravenous potassium cyanide or to baroreflex activation with intravenous phenylephrine or sodium nitroprusside were not modified by AV3V lesions. The results show that the integrity of the AV3V region is essential for the pressor responses to L-glutamate into the NTS but not for the pressor responses to chemoreflex activation, suggesting dissociation between the central mechanisms involved in these responses. (C) 2004 Elsevier B.V. All rights reserved.

Role of pressor mechanisms from the NTS and CVLM in control of arterial pressure

In the present study, we investigated the effects of inhibition of the caudal ventrolateral medulla (CVLM) with the GABA(A) agonist muscimol combined with the blockade of glutamatergic mechanism in the nucleus of the solitary tract (NTS) with kynurenic acid (kyn) on mean arterial pressure (MAP), heart rate (HR), and regional vascular resistances. In male Holtzman rats anesthetized intravenously with urethane/chloralose, bilateral injections of muscimol (120 pmol) into the CVLM or bilateral injections of kyn (2.7 nmol) into the NTS alone increased MAP to 186 +/- 11 and to 142 +/- 6 mmHg, respectively, vs. control: 105 +/- 4 mmHg; HR to 407 +/- 15 and to 412 +/- 18 beats per minute (bpm), respectively, vs. control: 352 +/- 12 bpm; and renal, mesenteric and hindquarter vascular resistances. However, in rats with the CVLM bilaterally blocked by muscimol, additional injections of kyn into the NTS reduced MAP to 88 +/- 5 mmHg and mesenteric and hindquarter vascular resistances below control baseline levels. Moreover, in rats with the glutamatergic mechanisms of the NTS blocked by bilateral injections of kyn, additional injections of muscimol into the CVLM also reduced MAP to 92 +/- 2 mmHg and mesenteric and hindquarter vascular resistances below control baseline levels. Simultaneous blockade of NTS and CVLM did not modify the increase in HR but also abolished the increase in renal vascular resistance produced by each treatment alone. The results suggest that important pressor mechanisms arise from the NTS and CVLM to control vascular resistance and arterial pressure under the conditions of the present study.

Central blockade of nitric oxide synthesis reduces moxonidine-induced hypotension

1 Nitric oxide (NO) and alpha(2)-adrenoceptor and imidazoline agonists such as moxonidine may act centrally to inhibit sympathetic activity and decrease arterial pressure.2 In the present study, we investigated the effects of pretreatment with L-NAME ( NO synthesis inhibitor), injected into the 4th ventricle (4th V) or intravenously (i.v.), on the hypotension, bradycardia and vasodilatation induced by moxonidine injected into the 4th V in normotensive rats.3 Male Wistar rats with a stainless steel cannula implanted into the 4th V and anaesthetized with urethane were used. Blood flows were recorded by use of miniature pulsed Doppler flow probes implanted around the renal, superior mesenteric and low abdominal aorta.4 Moxonidine (20 nmol), injected into the 4th V, reduced the mean arterial pressure (-42+/-3 mmHg), heart rate (-22+/-7 bpm) and renal (-62+/-15%), mesenteric (-41+/-8%) and hindquarter (-50+/-8%) vascular resistances.5 Pretreatment with L-NAME (10 nmol into the 4th V) almost abolished central moxonidine-induced hypotension (-10+/-3 mmHg) and renal (-10+/-4%), mesenteric (-11+/-4%) and hindquarter (-13+/-6%) vascular resistance reduction, but did not affect the bradycardia (-18+/-8 bpm).6 the results indicate that central NO mechanisms are involved in the vasodilatation and hypotension, but not in the bradycardia, induced by central moxonidine in normotensive rats. British Journal of Pharmacology (2004).

Antihypertensive responses elicited by central moxonidine in rats: Possible role of nitric oxide

In the present study, we investigated the effects of pretreatment with N-G-nitro-L-arginine methyl ester (L-NAME) (nitric oxide synthase inhibitor) injected intravenously (IV) on the hypotension, bradycardia, and vasodilation produced by moxonidine (alpha(2)-adrenergic/imidazoline receptor agonist) injected into the fourth brain ventricle (4th V) in rats submitted to acute hypertension that results from baroreflex blockade by bilateral injections of kynurenic acid (kyn, glutamatergic receptor antagonist) into the nucleus of the solitary tract (NTS) or in normotensive rats. Male Wistar rats (n = 5 to 7/group) anesthetized with IV urethane (1.0 g kg(-1) of body weight) and a-chloralose (60mg kg(-1) of body weight) were used. Bilateral injections of kyn (2.7 nmol 100 nL(-1)) into the NTS increased baseline mean arterial pressure (148 +/- 11 mm Hg, vs. control: 102 +/- 4mm Hg) and baseline heart rate (417 +/- 11 bpm, vs. control: 379 +/- 6 bpm). Moxonidine (20 nmol mu L-1) into the 4th V reduced mean arterial pressure and heart rate to similar levels in rats treated with kyn into the NTS (68 +/- 9 mm Hg and 359 +/- 7 bpm) or in control normotensive rats (66 +/- 7 mm Hg and 362 +/- 8 bpm, respectively). The pretreatment with L-NAME (2 5 mu mol kg-1, IV) attenuated the hypotension produced by moxonidine into the 4th V in rats treated with kyn (104 +/- 6 mm Hg) or in normotensive rats (95 +/- 8 mm Hg), without changing bradycardia. Moxonidine into the 4th V also reduced renal, mesenteric, and hindquarter vascular resistances in rats treated or not with kyn into the NTS and the pretreatment with L-NAME IV reduced these effects of moxonidine. Therefore, these data indicate that nitric oxide mechanisms are involved in hypotension and mesenteric, renal, and hindquarter vasodilation induced by central moxonidine in normotensive and in acute hypertensive rats.

Functional relationship between subfrnical organ cholinergic stimulation and nitrergic activation influencing cardiovascular and body fluid homeostasis

We have studied the effects of L-NG-nitro arginine methyl esther (L-NAME), L-arginine (LAR), inhibitor and a donating nitric oxide agent on the alterations of salivary flow, water intake, arterial blood pressure (MAP) and heart rate (HR) induced by the injection pilocarpine into the subfornical organ (SFO). Rats (Holtzman 250-300 g) were anesthetized with 2, 2, 2-tribromoethanol (20 mg/100 kg b. wt.) and a stainless steel carmula were implanted into their SFO. The volume of injection was 0.2 mu l. The amount of saliva secretion was studied over a 5-min period. Pilocarpine (40 mu g), L-NAME (40 mu g) and LAR (30 mu g) were used in all experiments for the injection into the SFO. Pilocarpine (10, 20, 40, 80 and 160 mu g) injected into SFO elicited a concentration-dependent increase in salivary secretion. L-NAME injected prior to pilocarpine into the SFO increased salivary secretion and water intake due to the effect of pilocarpine. LAR injected prior to pilocarpine into the SFO attenuated the salivary secretion and water intake. Pilocarpine, injected into the SFO increased the MAP and decreased heart rate (HR). L-NAME injected prior to pilocarpine into the SFO potentiated the pressor effect of pilocarpine with a decrease in HR. LAR injected into the SFO prior to pilocarpine attenuated the increase in MAP with no changes in HR. The present study suggests that the SFO nitrergic cells interfere in the cholinergic pathways implicated in the control of salivary secretion, fluid and cardiovascular homeostasis. (c) 2007 Elsevier B.V All rights reserved.

AV3V lesions reduce the pressor response to L-glutamate into the RVLM

Neurons from the rostral ventrolateral medulla (RVLM) directly activate sympathetic preganglionic neurons in the spinal cord. Hypertensive responses and sympathetic activation produced by different stimuli are strongly affected by lesions of the preoptic periventricular tissue surrounding the anteroventral third ventricle (AV3V region). Therefore, in the present study, we investigated the effects of acute (1 day) and chronic (IS days) electrolytic lesions of the AV3V region on the pressor responses produced by injections of the excitatory amino acid L-glutamate into the RVLM of unanesthetized rats. Male Holtzman rats with sham or electrolytic AV3V lesions and a stainless steel cannula. implanted into the RVLM were used. The pressor responses produced by injections of L-glutamate (1, 5 and 10 nmol/100 nl) into the RVLM were reduced 1 day (9 +/- 4, 39 +/- 6 and 37 +/- 4 mm Hg, respectively) and 15 days after AV3V lesions (13 +/- 6, 39 +/- 4 and 43 +/- 4 mm Hg, respectively, vs. sham lesions: 29 +/- 3, 50 +/- 2 and 58 +/- 3 mm Hg, respectively). Injections of L-glutamate into the RVLM in sham or AV3V-lesioned rats produced no significant change in the heart rate (HR). Baroreflex bradycardia and tachycardia produced by iv phenylephrine or sodium nitroprusside, respectively, and the pressor and bradycardic responses to chemoreflex activation with iv potassium cyanide were not modified by AV3V lesions. The results suggest that signals from the AV3V region are important for sympathetic activation induced by L-glutamate into the RVLM. (c) 2006 Elsevier B.V. All rights reserved.

Ablation of NK1 receptor bearing neurons in the nucleus of the solitary tract blunts cardiovascular reflexes in awake rats

The nucleus of the solitary tract (NTS) receives primary afferents involved in cardiovascular regulation. We investigated the role of NK1-receptor bearing neurons in the NTS on cardiovascular reflexes in awake rats fitted with chronic venous and arterial cannulae. These neurons were lesioned selectively with saporin conjugated with substance P (SP-SAP, 2 mu M, bilateral injections of 20 nL in the subpostremal NTS, or 200 nL in both the subpostremal and the commissural NTS). Before, and 7 and 14 days after injection of SP-SAP, we measured changes in blood pressure and heart rate induced by i.v. injection of phenylephrine and nitroprusside (baroreceptor reflex), cyanide (arterial chemoreceptor reflex), and phenylbiguanide (Bezold-Jarisch reflex). The smaller injections with SP-SAP completely abolished NK1 receptor staining in the subpostremal NTS. The larger injections abolished NK1 receptor immunoreactivity in an area that extended from the commissural NTS to the rostral end of the subpostremal NTS. The lesions seemed to affect only a limited number of neurons, since neutral red stained sections did not show any obvious reduction in cell number. The smaller lesions reduced the gain of baroreflex bradycardia and the hypotension induced by phenylbiguanide. The larger lesions completely abolished the response to phenylbiguanide, blocked the baroreflex bradycardia induced by phenylephrine, severely blunted the baroreflex tachycardia, and blocked the bradycardia and reduced the hypertension induced by cyanide. Thus, these responses depend critically on NK1-receptor bearing neurons in the NTS. (c) 2006 Elsevier B.V. All rights reserved.

Central cholinergic blockade reduces the pressor response to L-glutamate into the rostral ventrolateral medullary pressor area

Injections of the excitatory amino acid L-glutamate (L-glu) into the rostral ventrolateral medulla (RVLM) directly activate the sympathetic nervous system and increase mean arterial pressure (MAP). A previous study showed that lesions of the anteroventral third ventricle region in the forebrain reduced the pressor response to L-glu into the RVLM. In the present study we investigated the effects produced by injections of atropine (cholinergic antagonist) into the lateral ventricle (LV) on the pressor responses produced by L-ghl into the RVLM. Male Holtzman rats (280-320 g, n=5 to 12/group) with stainless steel cannulas implanted into the RVLM, LV or 4th ventricle (4th V) were used. MAP and heart rate (HR) were recorded in unanesthetized rats. After saline into the LV, injections of L-glu (5 nmol/100 nl) into the RVLM increased MAP (51 +/- 4 mm Hg) without changes in HR. Atropine (4 nmol/1 PI) injected into the LV reduced the pressor responses to L-glu into the RVLM (36 +/- 5 mm Hg), However, atropine at the same dose into the 4th V or directly into the RVLM did not modify the pressor responses to L-glu into the RVLM (45 +/- 2 and 49 +/- 4 mm Hg, respectively, vs. control: 50 +/- 4mmHg). Central cholinergic blockade did not affect baro and chemoreflex nor the basal MAP and HR. The results suggest that cholinergic mechanisms probably from forebrain facilitate or modulate the pressor responses to L-glu into the RVLM. The mechanism is activated by acetylcholine in the forebrain, however, the neurotransmitter released in the RVLM to facilitate the effects of glutamate is not acetylcholine. (C) 2007 Elsevier B.V. All rights reserved.

Involvement of central alpha(1)- and mu(2)-adrenoceptors on cardiovascular responses to moxonidine

In the present study we compared the effects produced by moxonidine (alpha(2)-adrenoceptor/imidazoline agonist) injected into the 4th cerebral ventricle and into the lateral cerebral ventricle on mean arterial pressure, heart rate and on renal, mesenteric and hindquarter vascular resistances, as well as the possible action of moxonidine on central alpha(1)- or alpha(2)-adrenoceptors to produce cardiovascular responses. Male Holtzman rats (n = 7-8) anesthetized with urethane (0.5 g/kg, intravenously - i.v.) and alpha-chloralose (60 mg/kg, i.v.) were used. Moxonidine (5, 10 and 20 nmol) injected into the 4th ventricle reduced arterial pressure (-19 +/- 5, -30 +/- 7 and -43 +/- 8 mmHg vs. vehicle: 2 +/- 4 mmHg), heart rate (-10 +/- 6, - 16 +/- 7 and -27 +/- 9 beats per minute - bpm, vs. vehicle: 4 +/- 5 bpm), and renal, mesenteric and hindquarter vascular resistances. Moxonidine (5, 10 and 20 nmol) into the lateral ventricle only reduced renal vascular resistance (-77 +/- 17%, - 85 +/- 13%, -89 +/- 10% vs. vehicle: 3 +/- 4%), without changes on arterial pressure, heart rate and mesenteric and hindquarter vascular resistances. Pre-treatment with the selective alpha(2)-adrenoceptor antagonist yohimbine (80, 160 and 320 nmol) injected into the 4th ventricle attenuated the hypotension (-32 +/- 5, -25 +/- 4 and -12 +/- 6 mmHg), bradycardia (-26 +/- 11, -23 +/- 5 and -11 +/- 6 bpm) and the reduction in renal, mesenteric and hindquarter vascular resistances produced by moxonidine (20 nmol) into the 4th ventricle. Pretreatment with yohimbine (320 nmol) into the lateral ventricle did not change the renal vasodilation produced by moxonidine (20 nmol) into the lateral ventricle. The alpha(1)-adrenoceptor antagonist prazosin (320 nmol) injected into the 4th ventricle did not affect the cardiovascular effects of moxonidine. However, prazosin (80, 160 and 320 nmol) into the lateral ventricle abolished the renal vasodilation (-17 +/- 4, -6 +/- 9 and 2 +/- 11%) produced by moxonidine. The results indicate that the decrease in renal vascular resistance due to moxonidine action in the forebrain is mediated by alpha(1)-adrenoceptors, while the cardiovascular effects produced by moxonidine acting in the brainstern depend at least partially on the activation of coadrenoceptors. (c) 2007 Elsevier B.V. All rights reserved.

Central moxonidine on salivary gland blood flow and cardiovascular responses to pilocarpine

Peripheral treatment with the cholinergic agonist pilocarpine induces intense salivation that is inhibited by central injections of the alpha(2)-adrenergic/imidazoline receptor agonist moxonidine. Salivary gland blood flow controlled by sympathetic and parasympathetic systems may affect salivation. We investigated the changes in mean arterial pressure (MAP) and in the vascular resistance in the submandibular/sublingual gland (SSG) artery, superior mesenteric (SM) artery and low abdominal aorta (hindlimb) in rats treated with intraperitoneal (i.p.) pilocarpine alone or combined with intracerebroventricular (i.c.v.) moxonidine. Male Holtzman rats with stainless steel cannula. implanted into lateral ventricle (LV) and anesthetized with urethane were used. Pilocarpine (4 mumol/kg of body weight) i.p. reduced SSG vascular resistance (-50 +/- 13% vs. vehicle: 5 +/- 3%). Pilocarpine i.p. also increased mesenteric vascular resistance (15 +/- 5% vs. vehicle: 2 +/- 3%) and MAP (16 +/- 3 mmHg, vs. vehicle: 2 +/- 3 mmHg). Moxonidine (20 nmol) i.c.v. increased SSG vascular resistance (88 +/- 12% vs. vehicle: 7 +/- 4%). When injected 15 min following i.c.v. moxonidine, pilocarpine i.p. produced no change on SSG vascular resistance. Pilocarpine-induced pressor responses and increase in mesenteric vascular resistance were not modified by i.c.v. moxonidine. The treatments produced no change in heart rate (HR) and hindlimb vascular resistance. The results show that (1) i.p. pilocarpine increases mesenteric vascular resistance and MAP and reduces salivary gland vascular resistance and (2) central moxonidine increases salivary gland vascular resistance and impairs pilocarpine-induced salivary gland vasodilatation. Therefore, the increase in salivary gland vascular resistance may play a role in the anti-salivatory response to central moxonidine. (C) 2003 Elsevier B.V. All rights reserved.

Lipopolysaccharide reduces sodium intake and sodium excretion in dehydrated rats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The bradycardic and hypotensive responses to serotonin are reduced by activation of GABA A receptors in the nucleus tractus solitarius of awake rats

We investigated the effects of bilateral injections of the GABA receptor agonists muscimol (GABA A) and baclofen (GABA B) into the nucleus tractus solitarius (NTS) on the bradycardia and hypotension induced by iv serotonin injections (5-HT, 2 µg/rat) in awake male Holtzman rats. 5-HT was injected in rats with stainless steel cannulas implanted bilaterally in the NTS, before and 5, 15, and 60 min after bilateral injections of muscimol or baclofen into the NTS. The responses to 5-HT were tested before and after the injection of atropine methyl bromide. Muscimol (50 pmol/50 nl, N = 8) into the NTS increased basal mean arterial pressure (MAP) from 115 ± 4 to 144 ± 6 mmHg, did not change basal heart rate (HR) and reduced the bradycardia (-40 ± 14 and -73 ± 26 bpm at 5 and 15 min, respectively, vs -180 ± 20 bpm for the control) and hypotension (-11 ± 4 and -14 ± 4 mmHg, vs -40 ± 9 mmHg for the control) elicited by 5-HT. Baclofen (12.5 pmol/50 nl, N = 7) into the NTS also increased basal MAP, but did not change basal HR, bradycardia or hypotension in response to 5-HT injections. Atropine methyl bromide (1 mg/kg body weight) injected iv reduced the bradycardic and hypotensive responses to 5-HT injections. The stimulation of GABA A receptors in the NTS of awake rats elicits a significant increase in basal MAP and decreases the cardiac Bezold-Jarisch reflex responses to iv 5-HT injections.

Cardiovascular responses to hydrogen peroxide into the nucleus tractus solitarius

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)