This study was undertaken to locate and characterise the neurons in the central nervous system that project to the kidney. In particular, the aim was to illustrate and characterise the neural link between regions in the hypothalamus known to influence renal function and fluid balance, and nerves known to innervate the kidney.

Hypertension affects one in two adults in the United States and contributes to more than 10% of deaths worldwide. The salt sensitivity of blood pressure, a clinical phenomenon present in one half of hypertensive patients and one quarter of normotensive individuals, predicts the development of hypertension. The prevalence of hypertension rises with age, and age-related increases in salt sensitivity and sympathetic nervous system activity, which promotes renal sodium reabsorption and plays a pathophysiological role in salt sensitivity and hypertension, have been documented. Increased mechanistic insight into the integrated renal and neural mechanisms influencing sodium homeostasis and blood pressure, particularly in aging, could yield valuable information for the phenotypically targeted treatment of hypertension. The renal nerves, comprised of the sensory afferent renal nerves (ARN) and the efferent renal sympathetic nerves, influence sodium homeostasis and blood pressure. The ARN, which include mechanosensitive and chemosensitive fibers, mediate a sympathoinhibitory reno-renal reflex that suppresses renal sympathetic nerve activity. The renal sympathetic nerves release norepinephrine, which can promote salt-sensitive hypertension in part by activating the sodium chloride cotransporter (NCC). In this thesis, Sprague Dawley rats were used as a model of normal aging to demonstrate that 1) the ARN are critical to the sympathoinhibitory and natriuretic responses to alterations in sodium homeostasis and protect against salt sensitivity of blood pressure, 2) the paraventricular nucleus of the hypothalamus may be a site of central integration of the mechanosensitive sympathoinhibitory reno-renal reflex, 3) norepinephrine promotes NCC activity through an α1-adrenoceptor-gated WNK1-OxSR1-dependent signaling pathway, driving salt-sensitive hypertension, and 4) impairments in the sympathoinhibitory reno-renal reflex may promote sympathoexcitation and NCC-mediated sodium retention, driving salt-sensitive hypertension in aging rats. Finally, data from the Genetic Epidemiology of Salt Sensitivity study were used to demonstrate that variance in the gene encoding Gαi2 proteins, which are upregulated in the paraventricular nucleus during high salt intake in salt-resistant animal models and are required for dietary sodium-evoked suppression of renal sympathetic outflow, may be a biomarker for the salt sensitivity of blood pressure in humans. Together, these findings highlight the integrated renal and neural mechanisms contributing to salt sensitivity and age-related hypertension.

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Of the factors that can promote hypertension, food behavior is highlighted in relation to unhealthy eating habits present in western diet. Thus, present study sought to evaluate some aspects of this pathology in several situations, and themes were discussed separately in two chapters. In the first moment, effect of maternal hyperlipidic diet on metabolic and autonomic parameters in offspring was evaluated. It is known which obesity induced by maternal diet can modify central regulatory pathways of the fetus, mainly long-term regulation of appetite, but no work sought to evaluate the influence of the maternal hyperlipidic diet (HD) on cardiovascular and autonomic parameters in the offspring . Female Holtzman rats (280-300 g) were divided into two groups. One group received standard diet (SD) and other HD. The animals had free access to SD or HD for 6 weeks prior and during gestation and lactation period. All pups were weaned after 21 days of life and had free access to SD. After one week some offspring and mothers were submitted to glycemic test and later euthanized for removal of adipose tissue and blood. Other offspring were submitted to in situ preparation. DH increased adipose tissue in all females, but was able to change only metabolic triacylglycerols concentration. Offspring of HFD dams (OffHFD) showed an increase in adipose tissue and total cholesterol and HDL levels. Offspring of SD dams (OffSD) showed decrease in sympathetic activity after pre-colicular transection. This effect was not observed in males offspring of mothers with HFD (OffHFD). KCN infusion caused similar increases in abdominal activity (ABD), in phrenic nerve frequency (PNA f) and sympathetic activity (SNA), but in OffHFD this increase in SNA was smaller. KCN caused increase in phrenic nerve amplitude (PNA) and was higher in OffHFD. Hypercapnia resulted in increase in SNA, ABD and PNA and decrease in PNA f in both groups. The decrease in PNA f was more pronounced in OffHFD and increased PNA was higher in OffHFD. Phenylephrine caused in both groups decrease in SNA, ABD and PNA, and generated an increase in PNA f. The reduction of SNA was higher in OffHFD. These results suggest that maternal HFD during fetal development alters central connections in offspring. In second moment oxytocin effects on vascular reactivity and its role in hypernatremia-induced responses were evaluated. Changes in volume and/or extracellular compartments composition are known to evoke various autonomic, cardiovascular and hormonal responses that to modulate renal excretion of water and sodium. The main vegetative adjustments are: renal vasodilation and oxytocin secretion. Regulation of osmolarity and volume is critical for survival. Despite knowledge, no study evaluated interaction between renal sympathetic activity and oxytocin secretion on renal and cardiovascular responses induced by sodium overload. Male Wistar rats (280–350 g) were anesthetized with sodium thiopental (40 mg/kg, i.v.). Animals were also instrumented for measurement of mean arterial pressure (MAP) and renal blood flow (RBF). Renal vascular conductance (RVC) was calculated as the ratio of RBF by MAP. In anesthetized rats (n = 6), OT infusion (0.03 μg/kg, i.v.) induced renal vasodilation. Ex vivo experiments demonstrated that OT caused renal artery relaxation. Blockade of OT receptors (OTR) reduced these responses to OT, indicating a direct effect of this peptide on OTR on this artery. Hypertonic saline (3 M NaCl, 1.8 ml/kg b.wt., i.v.) was infused over 60 s. In sham rats (n=6), hypertonic saline induced renal vasodilation. The OXTR antagonist (AT; n=7) and renal denervation (RX) reduced the renal vasodilation induced by hypernatremia. Atosiban with renal denervation (RX+AT; n=7) completely abolished renal vasodilation induced by sodium overload. Intact rats excreted 51% of the injected sodium within 90 min. Natriuresis was slightly blunted by atosiban and renal denervation (42% and 42% of load, respectively), whereas atosiban with renal denervation reduced sodium excretion to 16% of the load. These results suggest that OT and renal nerves are involved in renal vasodilation and natriuresis induced by acute plasma hypernatremia. The understanding of regulatory mechanisms activated both during obesity and during hyperosmolarity allows greater possibility development new therapeutic tools for hypertension prevention and treatment. / A hipertensão arterial é uma das patologias mais comuns que afetam a população. Dentre os fatores que podem propiciar a hipertensão o comportamento alimentar ganha destaque no que se referem aos hábitos alimentares não saudáveis presentes na dieta ocidental. Sendo assim, o presente trabalho procurou avaliar alguns aspectos dessa patologia em diversas situações, e os temas foram discutidos de forma separada em dois capítulos. No primeiro momento avaliou-se o efeito da dieta hiperlipídica materna sobre os parâmetros metabólicos e autonômicos na prole. Sabe-se que a obesidade induzida pela dieta materna pode modificar os caminhos regulatórios centrais do feto, principalmente a regulação em longo prazo do apetite, porém nenhum trabalho procurou avaliar a influência da dieta hiperlipídica (DH) materna sobre os parâmetros cardiovasculares e autonômicos na prole. Ratas Holtzman adultas (280 - 300 g) foram divididas em dois grupos. Um grupo recebeu dieta padrão (DP) e o outro grupo DH. Os animais tiveram acesso livre a DP ou DH durante 6 semanas prévias (período de pré-gestação) e durante período de gestação e lactação. Todos os filhotes foram desmamados após 21 dias de vida e tiveram livre acesso a DP. Após uma semana alguns filhotes e as mães foram submetidos ao teste glicêmico e posteriormente eutanasiadas para retirada de tecido adiposo e sangue. Os outros filhotes foram submetidos à preparação coração-bulbo-hipotálamo (in situ). A DH aumentou o tecido adiposo nas ratas, mas foi capaz de alterar apenas as concentrações metabólicas de triacilgliceróis nesses animais. Filhotes machos de mães com DH (FMDH) apresentaram aumento no tecido adiposo, aumento nos níveis de colesterol total e nos níveis de HDL. Filhotes machos de mães com DP (FMDP) apresentaram redução da atividade simpática após transecção pré-colicular. Esse efeito não foi observado nos FMDH. A infusão de KCN provocou aumentos similares entre FMDP e FMDH quanto à atividade abdominal (ABD), na frequência do nervo frênico (f PNA) e na atividade simpática torácica (SNA), porém, no grupo FMDH esse aumento na SNA foi menor. O KCN provocou um aumento na amplitude do nervo frênico (PNA) sendo maior em FMDH. A hipercapnia provocou nos filhotes um aumento na SNA, na ABD e na PNA e gerou uma diminuição na f PNA em ambos os grupos. A diminuição na f PNA foi mais acentuada em FMDH e o aumento da PNA foi maior em FMDH. A fenilefrina provocou nos dois grupos uma diminuição na SNA, na ABD e na PNA, e gerou um aumento na f PNA. A simpatoinibição foi maior em FMDH. Esses resultados sugerem que a DH materna durante desenvolvimento fetal provavelmente altera as conexões centrais na prole. No segundo momento avaliou-se os efeitos da ocitocina sobre a reatividade vascular e seu papel nas respostas induzidas pela hipernatremia. Sabe-se que alterações no volume e/ou na composição dos compartimentos extracelulares evocam várias respostas autonômicas, cardiovasculares e hormonais que atuam em conjunto para modular a excreção renal de água e sódio. Os principais ajustes vegetativos são: vasodilatação renal e secreção de ocitocina. A regulação da osmolaridade e do volume é fundamental para sobrevivência. Apesar do vasto conhecimento na área nenhum estudo avaliou a interação entre a atividade simpática renal e a secreção de ocitocina sobre as respostas renais e cardiovasculares induzidas pela sobrecarga de sódio. Ratos Wistar machos (280-350 g) foram anestesiados e instrumentalizados para implantação de cateteres na bexiga, na veia e na artéria femoral e também para medição da pressão arterial média (PAM) e fluxo sanguíneo renal (FSR). Em ratos anestesiados (n = 6), a infusão de OT (0,03 μg/kg, i.v.) induziu vasodilatação renal. Em experimentações ex vivo a OT causou relaxamento da artéria renal. O bloqueio dos receptores de OT (OTR) reduziu essas respostas à OT, indicando um efeito direto desse peptídeo em seu receptor nesta artéria. O bloqueio dos receptores de ocitocina e a desnervação renal reduziu a vasodilatação renal e natriurese induzida pela sobrecarga de sódio aguda e a combinação do antagonista de receptores de ocitocina e a desnervação renal aboliram completamente a vasodilatação renal e reduziram ainda mais a natriurese induzida pela hipernatremia. Estes resultados sugerem que a OT e os nervos renais estão envolvidos na vasodilatação renal e natriurese induzida por hipernatremia aguda. O amplo conhecimento na área e a compreensão dos mecanismos regulatórios ativados tanto durante a obesidade quanto durante hiperosmolaridade permite uma maior possibilidade de desenvolvimento de novas ferramentas terapêuticas para a prevenção e tratamento da hipertensão.