Efeitos da restri??o alimentar sobre o sistema renina angiotensina e sua influ?ncia nas respostas cardiovasculares de ratas Fischer.

Programa de P?s-Gradua??o em Ci?ncias Biol?gicas. N?cleo de Pesquisas em Ci?ncias Biol?gicas, Pr?-Reitoria de Pesquisa de P?s Gradua??o, Universidade Federal de Ouro Preto.Introdu??o: Insufici?ncia card?aca, desregula??o auton?mica, hipotens?o e bradicardia s?o problemas comuns nos casos de restri??o alimentar (RA) severa e ? bem estabelecido que o sistema renina angiotensina aldosterona (SRAA) ? importante no controle da press?o arterial atrav?s da a??o sobre v?rios ?rg?os. Entretanto pouco se sabe sobre o SRAA e sua influ?ncia nas respostas cardiovasculares na RA. Objetivo: N?s avaliamos o efeito da RA na via metab?lica da Ang-[1-8] na regula??o da press?o arterial para investigar como a RA pode causar hipotens?o enquanto simultaneamente aumenta a atividade do sistema nervoso simp?tico. Metodologia e Resultados: Foram usadas ratas Fischer mantidas em dieta controle (CT), ad libitum, ou RA (60%) por 14 dias. O efeito da Ang-[1-8] sobre a press?o arterial m?dia (PAM) foi menor nos animais com RA mesmo ocorrendo uma ativa??o maior da via metab?lica da Ang-[1-8]. O metabolismo da Ang-[1-10] e seu precursor angiotensinog?nio (AGT), foram aumentados pela RA como evidenciado pelo aumento da atividade da enzima conversora de angiotensina (ECA) plasm?tica e elevada concentra??o de Ang-[1-8]. Ap?s a infus?o de Ang-[1-10], houve tamb?m aumento na concentra??o de AGT e na convers?o da Ang-[1-10] para outros metab?litos de angiotensina incluindo Ang-[2-10], Ang-[2-8] e Ang-[3-8]. Embora a Ang-[1-8] causou uma resposta pressora menor na RA, foi encontrado que o RNAm para o receptor AT1 foi aumentado em vasos mesent?ricos enquanto nenhuma altera??o foi observada na express?o dos receptores AT2 e Mas. Al?m da express?o, a responsividade do receptor AT1 na RA foi aumentada ap?s infus?o de losartan. Entretanto, ap?s infus?o de fenilefrina, a amplitude da resposta pressora foi a mesma que a observada no grupo CT. Conclus?o: Nossos resultados sugerem que as vias metab?licas da angiotensina est?o ativadas constantemente no modelo de RA aumentando a concentra??o plasm?tica da Ang-[1-8] e seus pept?deos downstream em compensa??o a hipotens?o, bradicardia e hipovolemiaRationale: Heart failure, autonomic imbalance, hypotension and bradycardia are common problem in anorexia nervosa (AN) and is well known that the angiotensin system is important to control the blood pressure through many organs, however nothing is known about the angiotensin (Ang) system and its influence in the cardiovascular responses in AN. Objective: We examined the effect of food restriction (FR) on Ang-[1-8] metabolic pathways in blood pressure regulation to investigate how FR can cause hypotension while simultaneously increasing the sympathetic nervous system. Methods and Results We used female Fischer rats maintained on a control (CT) or severe FR (60%) diet for 14 days. The mean arterial pressure (MAP) response to Ang-[1-8] was attenuated in FR rats even though the systemic Ang-[1-8] metabolic pathway was activated. Metabolism of Ang-[1-10] and its precursor, angiotensinogen, were increased by FR as evidenced by increased plasma angiotensin converting enzyme (ACE) activity and elevated plasma Ang-[1-8] and angiotensinogen levels before and after Ang-[1-10] infusion. There was also increased conversion of Ang-[1-10] to other angiotensin metabolites including Ang-[2-10], Ang-[2-8] and Ang-[3-8]. Although Ang-[1-8] causes a lower MAP response, we found that AT1R mRNA expression was increased in mesenteric vessels whereas no differences were observed in the mRNA expression of angiotensin type 2 receptor (AT2R) and mas receptor (masR). Furthermore, the AT1 blockage with losartan caused a higher depressor effect in FR, even no difference was seen in the maximum BP response with phenylephrine infusion. Conclusions: Our results suggest that angiotensin metabolic pathways are constantly activated in FR model to increase the Ang-[1-8] and its downstream peptides in order to compensate for the hypotension, bradycardia and hypovolemia

Role of the Renin Angiotensin System in Blood Pressure Allostasis-induced by Severe Food Restriction in Female Fischer rats

Severe food restriction (FR) is associated with blood pressure (BP) and cardiovascular dysfunction. The renin-angiotensin system (RAS) regulates BP and its dysregulation contributes to impaired cardiovascular function. Female Fischer rats were maintained on a control (CT) or severe FR (40% of CT) diet for 14 days. In response to severe FR, BP allostasis was achieved by up-regulating circulating Ang-[1-8] by 1.3-fold through increased angiotensin converting enzyme (ACE) activity and by increasing the expression of AT1Rs 1.7-fold in mesenteric vessels. Activation of the RAS countered the depressor effect of the severe plasma volume reduction (≥30%). The RAS, however, still underperformed as evidenced by reduced pressor responses to Ang-[1-8] even though AT1Rs were still responsive to the depressor effects of an AT1R antagonist. The aldosterone (ALDO) response was also inadequate as no changes in plasma ALDO were observed after the large fall in plasma volume. These findings have implications for individuals who have experienced a period(s) of severe FR (e.g., anorexia nervosa, dieters, natural disasters) and suggests increased activity of the RAS in order to achieve allostasis contributes to the cardiovascular dysfunction associated with inadequate food intake

Role of the renin angiotensin system in blood pressure allostasis-induced by severe food restriction in female Fischer rats.

Severe food restriction (FR) is associated with blood pressure (BP) and cardiovascular dysfunction. The renin-angiotensin system (RAS) regulates BP and its dysregulation contributes to impaired cardiovascular function. Female Fischer rats were maintained on a control (CT) or severe FR (40% of CT) diet for 14 days. In response to severe FR, BP allostasis was achieved by up-regulating circulating Ang-[1?8] by 1.3-fold through increased angiotensin converting enzyme (ACE) activity and by increasing the expression of AT1Rs 1.7-fold in mesenteric vessels. Activation of the RAS countered the depressor effect of the severe plasma volume reduction (?30%). The RAS, however, still underperformed as evidenced by reduced pressor responses to Ang-[1?8] even though AT1Rs were still responsive to the depressor effects of an AT1R antagonist. The aldosterone (ALDO) response was also inadequate as no changes in plasma ALDO were observed after the large fall in plasma volume. These findings have implications for individuals who have experienced a period(s) of severe FR (e.g., anorexia nervosa, dieters, natural disasters) and suggests increased activity of the RAS in order to achieve allostasis contributes to the cardiovascular dysfunction associated with inadequate food intake

New insights on amygdala : basomedial amygdala regulates the physiological response to social novelty.

The amygdala has been associated with a variety of functions linked to physiological, behavioral and endocrine responses during emotional situations. This brain region is comprised of multiple sub-nuclei. These subnuclei belong to the same structure, but may be involved in different functions, thereby making the study of each sub-nuclei important. Yet, the involvement of the basomedial amygdala (BMA) in the regulation of emotional states has yet to be defined. Therefore, the aim of our study was to investigate the regulatory role of the BMA on the responses evoked during a social novelty model and whether the regulatory role depended on an interaction with the dorsomedial hypothalamus (DMH). Our results showed that the chemical inhibition of the BMA by the microinjection of muscimol (c-aminobutyric acid (GABAA) agonist) promoted increases in mean arterial pressure (MAP) and heart rate (HR), whereas the chemical inhibition of regions near the BMA did not induce such cardiovascular changes. In contrast, the BMA chemical activation by the bilateral microinjection of bicuculline methiodide (BMI; GABAA antagonist), blocked the increases in MAP and HR observed when an intruder rat was suddenly introduced into the cage of a resident rat, and confined to the small cage for 15 min. Additionally, the increase in HR and MAP induced by BMA inhibition were eliminated by DMH chemical inhibition. Thus, our data reveal that the BMA is under continuous GABAergic influence, and that its hyperactivation can reduce the physiological response induced by a social novelty condition, possibly by inhibiting DMH neurons

Influência da restrição alimentar no controle da pressão arterial sistêmica.

Anorexia nervosa é caracterizada por alterações psicológicas que ocasionam uma distorção da imagem corporal, um medo extremo de engordar e uma redução voluntária na ingestão alimentar. Esses pacientes muitas vezes desenvolvem alterações cardiovasculares, as quais são consideradas a principal causa de morte. Na impossibilidade de desenvolver experimentos com humanos, modelos experimentais que apresentam alterações semelhantes à anorexia tornam-se necessários para uma melhor compreensão da patologia. O modelo de restrição alimentar (RA) utilizado consiste na redução de 60% da quantidade de micro e macronutrientes oferecidos durante 14 dias. No 14º dia o grupo controle e RA foram subdivididos em três grupos experimentais: central, periférico e dosagens bioquímicas. Após o período de dieta, observamos que a mesma diminuiu o peso corporal dos animais e gerou alterações bioquímicas e fisiológicas semelhantes as que ocorrem na anorexia. As alterações bioquímicas foram diminuição da albumina plasmática, colesterol total e LDL, AST e ureia, juntamente com aumento na concentração de glicose e creatinina. Já as alterações fisiológicas foram anestro, diminuição da pressão arterial média (PAM) e da frequência cardíaca (FC). Também observamos edema cerebral e pulmonar e diminuição no peso do coração, rim e fígado, segundo peso absoluto. Posteriormente, testamos os sistemas que controlam a pressão arterial e a RA diminuiu o óxido nítrico plasmático e ocasionou uma resposta hipotensora maior após estimulação periférica do reflexo Bezold- Jarisch. Esse mesmo perfil de resposta foi observado após inibição periférica dos receptores α1 adrenérgico, porém quando bloqueamos os receptores β adrenérgicos houve uma resposta pressora menor. A infusão de Ang I aumentou mais a PAM nos animais RA, a qual posteriormente foi abolida pelo captopril. Quando colocamos Ang II por via endovenosa ou intracerebroventricular a resposta pressora foi menor na restrição em ambas as vias de administração. No bloqueio dos receptores AT1 centrais houve uma hipotensão mais acentuada que não foi observada no teste periférico e após dosagem da concentração de Ang II plasmática não houve diferença. Contudo, podemos dizer que o protocolo de restrição alimentar foi eficiente em desenvolver alterações bioquímicas e fisiológicas semelhantes as da anorexia nervosa diminuiu a concentração de óxido nítrico plasmático, aumentou a atividade simpática no vaso e aumentou a resposta hipotensora do reflexo Bezold-Jarisch. No sistema renina angiotensina, ocorreu uma resposta pressora reduzida após infusão de Ang II nos animais submetidos à restrição alimentar, também houve um aumento da responsividade após infusão de angiotensina I dependente de ECA juntamente com um aumento da atividade do receptor AT1.Anorexia nervosa is characterized by psychological changes that cause a distortion of body image, extreme fear of gaining weight and voluntary reduction in food intake. These patients often develop cardiovascular changes, which are considered the leading cause of death. Failing to develop human experiments, experimental models showing changes similar to anorexia become necessary for a better understanding of the pathology. The model of food restriction (FR) used was the restriction of 60% including macro and micro nutrients during 14 days. After the diet period, the control group and FR were divided in three experimental groups: central, peripheral and biochemical measurements. 14 days food restriction decreased body weight of the rats and produced biochemical and physiological changes that simulated anorexia nervosa symptoms. The biochemical alterations observed were reduction in plasma albumin, total cholesterol, LDL cholesterol, AST and urea. At the same time, there were increases in plasmatic concentrations of glucose and creatinine. The physiological changes observed were anestrus, hypotension and bradycardia. We have also detected cerebral and lung edema with reduction in heart, kidney and liver weight. Subsequently, we tested the systems that control blood pressure. Plasma nitric oxide was reduced in FR rats. FR rats presented a greater hypotensive response after peripheral stimulation of the Bezold-Jarisch reflex and inhibition of peripheral α1 adrenergic receptors. After blockage of β-adrenergic receptors there was a smaller pressor response in FR rats. The infusion of iv. Ang I increased blood pressure in FR, which was abolished by iv captopril. The pressor response was induced by iv and icv AngII was lower in food restricted animals. After the central blockage of AT1 receptors, in periventricular areas of lateral ventricle, there was a more pronounced hypotension which was not observed after the peripheral infusion. Interestingly, the plasma concentration of Ang II was not different between control and FR. Thus, we can conclude that food restriction protocol was effective in developing biochemical and physiological changes similar to those observed in anorexia nervosa in humans. Food restriction decreased plasma nitric oxide concentration, increased sympathetic activity in the vessel and increased the hypotensive response of Bezold-Jarisch reflex. In the renin-angiotensin system, there was a reduced pressor response after infusion of Ang II in animals subjected to dietary restriction. On the other hand, the pressor response of Ang I was increased and dependent on ECA. A possible increase in AT1 receptor activity could be prevent in the model contributing, with the increased sympathetic activity, in maintenance of blood pressure in FR rats

Increased α1-adrenoreceptor activity is required to sustain blood pressure in female rats under food restriction.

Aims: Weevaluated the effect of food restriction (FR) on the various reflexes involved in short termcardiovascular regulation; we also evaluated the contribution of the sympathetic nervous systemand of the plasmatic nitric oxide (NO) in the development of the counterregulatory cardiovascular changes triggered by FR. Main methods: Female rats were subjected to FR for 14 days, and after this period biochemical measurements of biochemical parameterswere performed. For physiological tests, animalswere anaesthetised, and a catheter was inserted into the femoral artery and vein for the acquisition of blood pressure and heart hate, and drug infusion, respectively.We then tested the Bezold–Jarisch reflex, the baroreflex and chemoreflex and the effect of the infusion of adrenergic receptor antagonists in control and food restricted animals. Key findings: The rats subjected to severe FR presented biochemical changes characteristic ofmalnutrition with a great catabolic state. FR also led to hypotension and bradycardia besides reducing the plasmatic concentration of NO. Moreover, activation of the Bezold–Jarisch reflex induced a more pronounced hypotensive response in animals subjected to FR. Intravenous infusion of a α1-adrenoreceptor antagonist induced a greater hypotensive response and a more pronounced tachycardic response in animals under food restriction,while the infusion of β- adrenoreceptor antagonist induced lower increases in blood pressure in these animals. Significance: Our results suggest that an increased α1-adrenoreceptor activity in the resistance arteries coupled with a reduction of plasmatic NO contributes in a complementary manner to maintain the blood pressure levels in animals under FR

High fat diet induced-obesity facilitates anxiety-like behaviors due to GABAergic impairment within the dorsomedial hypothalamus in rats.

Overweight and obesity are conditions associated with an overall range of clinical health consequences, and they could be involved with the development of neuropsychiatric diseases, such as generalized anxiety disorder (GAD) and panic disorder (PD). A crucial brain nuclei involved on the physiological functions and behavioral responses, especially fear, anxiety and panic, is the dorsomedial hypothalamus (DMH). However, the mechanisms underlying the process whereby the DMH is involved in behavioral changes in obese rats still remains unclear. The current study further investigates the relation between obesity and generalized anxiety, by investigating the GABAA sensitivity to pharmacological manipulation within the DMH in obese rats during anxiety conditions. Male Wistar rats were divided in two experimental groups: the first was fed a control diet (CD; 11% w/w) and second was fed a high fat diet (HFD; 45% w/w). Animals were randomly treated with muscimol, a GABAA agonist and bicuculline methiodide (BMI), a GABAA antagonist. Inhibitory avoidance and escape behaviors were investigated using the Elevated T-Maze (ETM) apparatus. Our results revealed that the obesity facilitated inhibitory avoidance acquisition, suggesting a positive relation between obesity and the development of an anxiety-like state. The injection of muscimol (an anxiolytic drug), within the DMH, increased the inhibitory avoidance latency in obese animals (featuring an anxiogenic state). Besides, muscimol prolonged the escape latency and controlling the possible panic-like behavior in these animals. Injection of BMI into the DMH was ineffective to produce an anxiety-like effect in obese animals opposing the results observed in lean animals. These findings support the hypotheses that obese animals are susceptible to develop anxiety-like behaviors, probably through changes in the GABAergic neurotransmission within the DMH

Blunted gaba-mediated inhibition within the dorsomedial hypothalamus potentiates the cardiovascular response to emotional stress in rats fed a high-fat diet.

Rats fed a high-fat diet (HFD) present an exaggerated endocrine response to stress conditions, which, like obesity, show a high correlation with cardiovascular diseases. Meanwhile the GABAergic neurotransmission within the dorsomedial hypothalamus (DMH) is involved in the regulation of the physiological responses during emotional stress. Here we evaluated the influence of obesity, induced by a HFD, on the cardiovascular responses induced by air jet stress in rats, and the role of the GABAergic tonus within the DMH in these changes. Our results showed that consumption of a HFD (45% w/w fat) for 9 weeks induced obesity and increases in baseline mean arterial pressure (MAP) and heart rate (HR). Moreover, obesity potentiated stress responsiveness, evidenced by the greater changes in MAP and HR induced by stress in obese rats. The injection of muscimol into the DMH reduced the maximal increases in HR and MAP induced by stress in both groups; however, the reduction in the maximal increases in MAP in the HFD group was less pronounced. Moreover, the injection of muscimol into the DMH of obese rats was less effective in reducing the stress-induced tachycardia, since the HR attained the same levels at the end of the stress paradigm as after the vehicle injection. Injection of bicuculline into DMH induced increases in MAP and HR in both groups. Nevertheless, obesity shortened the tachycardic response to bicuculline injection. These data show that obesity potentiates the cardiovascular response to stress in rats due to an inefficient GABAA-mediated inhibition within the DMH

Estrogen receptor ? activation within dorsal raphe nucleus reverses anxiety-like behavior induced by food restriction in female rats.

Severe food restriction (FR), as observed in disorders like anorexia nervosa, has been associated to the reduction of estrogen levels, which in turn could lead to anxiety development. Estrogen receptors, mainly ER? type, are commonly found in the dorsal raphe nucleus (DRN) neurons, an important nucleus related to anxiety modulation and the primary source of serotonin (5-HT) in the brain. Taking together, these findings suggest an involvement of estrogen in anxiety modulation during food restriction, possibly mediated by ER? activation in serotonergic DRN neurons. Thus, the present study investigated the relationship between food restriction and anxiety-like behavior, and the involvement of DRN and ER? on the modulation of anxiety-like behaviors in animals subjected to FR. For that, female Fischer rats were grouped in control group, with free access to food, or a FR group, which received 40% of control intake during 14 days. Animals were randomly treated with 17?-estradiol (E2), DPN (ER? selective agonist), or their respective vehicles, PBS and DMSO. Behavioral tests were performed on Elevated T-Maze (ETM) and Open Field (OF). Our results suggest that FR probably reduced the estrogen levels, since the remained in the non-ovulatory cycle phases, and their uterine weight was lower when compared to control group. The FR rats showed increased inhibitory avoidance latency in theETM indicating that FR is associated with the development of an anxiety-like state. The injections of both E2 and DPN into DRN of FR animals had an anxiolytic effect. Those data suggest thatanxiety-like behavior induced by FR could be mediated by a reduction of ER? activation in the DRN neurons, probably due to decreased estrogen levels

Amygdalar neuronal activity mediates the cardiovascular responses evoked from the dorsolateral periaqueductal gray in conscious rats.

There is ample evidence that both lateral/ dorsolateral periaqueductal gray (l/dlPAG) and basolateral amygdala (BLA) are essential for the regulation of the autonomic responses evoked during innate reactions to threatening stimuli. However, it is not well established to what extent the BLA regulates the upstream functional connection from the l/dlPAG. Here we evaluated the role of the BLA and its glutamatergic receptors in the cardiovascular responses induced by l/dlPAG stimulation in rats. We examined the influence of acute inhibition of the BLA, unilaterally, by injecting muscimol on the cardiovascular responses evoked by the injection of N-methyl D-aspartate (NMDA) into the l/dlPAG. We also evaluated the role of BLA ionotropic glutamate receptors in these responses by injecting antagonists of NMDA and AMPA/kainate receptor subtypes into the BLA. Our results show that the microinjection of NMDA in the BLA increased the mean arterial pressure (MAP) and heart rate (HR). Injection of NMDA into the l/dlPAG caused similar increases in these variables, which was prevented by the prior injection of muscimol, a GABAA agonist, into the BLA. Moreover, injection of glutamatergic antagonists (2-amino-5-phosphonopentanoate (AP5) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)) into the BLA reduced the increase in MAP and HR induced by l/dlPAG activation. Finally, the inhibition of the central amygdala neurons failed to reduce the cardiovascular changes induced by l/dlPAG activation. These results indicate that physiological responses elicited by l/dlPAG activation require the neuronal activity in the BLA. This ascending excitatory pathway from the l/dlPAG to the BLA might ensure the expression of the autonomic component of the defense reactio