During exercise water and electrolytes are lost in sweat. There is a large variation in both sweat rate and sweat composition and as a consequence sweat electrolyte loss can be large, especially for sodium, the primary cation in sweat. The loss of large amounts of sodium in sweat has been linked with hyponatraemia and muscle cramps. Sodium intake is encouraged in some athletes and in some exercise situations, which is in direct contrast to guidelines aimed at the general population aimed at reducing average sodium intakes to 2.4g of sodium per day (6g salt/day). Dietary sodium intakes have been determined by numerous methods, including weighed dietary records and 24h urine collections. As dietary sodium intake in excess of basal requirement is primarily excreted in the urine in non-sweating individuals, and the basal requirement for sodium is small, 24h urine collections can provide an accurate estimate of dietary sodium intake. In Chapter 3, 24h urinary sodium excretion was measured in eighteen subjects on 4 separate occasions. Subjects consumed their normal diet with the exception of a 5g creatine supplement and 500ml of water, which was part of a separate investigation. The relationship between urine sodium excretion in each 24h collection period was weak, but on average males excreted 200 ± 48mmol of sodium per day and females excreted 157 ± 33mmol of sodium per day, which is equivalent to 4.6g and 3.6g of sodium, respectively. This is in excess of the current recommended intake. In chapter 4, the variation in sodium excretion was determined in eight subjects who consumed the same diet for 5 consecutive days. Despite the similar intake of sodium each day, a day to day variation in sodium excretion of 13% was still observed. This was not related to either sodium intake or potassium intake. In chapter 5, nine subjects consumed their normal diet for 5 consecutive days but weighed and recorded all food and drink consumed. During this period, 24h urine samples were also collected. No strenuous exercise was permitted apart from an exercise task on day 4. This involved intermittent cycling in the heat until 2% body mass (BM) was lost. Sweat was collected from four absorbent patches placed on the back, chest, forearm and thigh. Sweat sodium concentration was adjusted to account for the 35% over-estimation using this regional collection method. Subjects lost 1.51 ± 0.19L of sweat and 66 ± 16mmol (range 32 86mmol) of sodium. There was no difference in sodium balance between each 24h period due to a significant decrease in urine sodium excretion on the day of exercise (day 4). In chapter 6, the effect of prior exercise on sweat composition during a second exercise bout completed later that same day was determined. Eight healthy males cycled for 40 minutes in the heat on one or two occasions. A period of 5h elapsed between exercise bouts when two exercise sessions were performed. Sweat was collected using a whole body washdown method and by 4 absorbent patches placed on the back, chest, forearm and thigh. The main finding was that prior exercise did not affect sweat rate or sweat sodium, potassium and chloride concentrations in the second exercise bout when using the whole body washdown method. Chapter 7 determined the effects of two exercise sessions completed on the same day on electrolyte balance. Nine subjects followed their normal dietary behaviour but weighed and recorded all food and drink consumed during 5 consecutive days. During this period 24h urine samples were also collected. No strenuous exercise was permitted during this period apart from two exercise tasks on day 4. During exercise sweat was collected using a whole body washdown technique. Sweat rate and sweat sodium, potassium and chloride concentrations during the second exercise bout were found to be similar to the first exercise bout. Subjects lost 2.64L (range 1.80 3.48L) of sweat and 138 ± 106mmol of sodium (range 32 287mmol). Sodium balance was not significantly affected on the day of exercise, but urine sodium was lower than dietary sodium intake on the day of exercise (Day 4) and the day following exercise (day 5), indicating significant sodium conservation by the kidney. In contrast, no change in sodium intake was observed. In chapter 8, the effect of skimmed milk and a sports drink in restoring fluid balance was examined following exercise-induced dehydration. Seven physically active males cycled intermittently in the heat until 2% BM was lost. During a 1h rehydration period a sports drink (23mmol Na+/L) or skimmed milk (32mmol Na+/L) was consumed in a volume equivalent to 150% of BM loss. Fluid balance at the end of the 3h recovery period tended to be more positive when milk was consumed. Despite this, no difference in exercise capacity in the heat was observed. This thesis shows that exercise did not increase sodium intake, but this may be due to the already high dietary sodium intake of individuals. Sodium balance was maintained in the majority of individuals due to a significant conservation of sodium by the kidneys. When sweat sodium losses are large, urine sodium conservation may not be sufficient to prevent a negative sodium balance. When no food is consumed in the acute period post-exercise, the higher sodium content of skimmed milk than a sports drink may be partly responsible for the increased retention of the ingested fluid. But this did not enhance subsequent performance in the heat.

Submitted by Ana Maria Fiscina Sampaio (fiscina@bahia.fiocruz.br) on 2012-11-19T18:59:36Z No. of bitstreams: 1 Atila dos Santos Batista. Papel dos receptores....pdf: 4517971 bytes, checksum: 2d9cb0d434dcb66027ca90861bbd1a75 (MD5) / Made available in DSpace on 2012-11-19T18:59:36Z (GMT). No. of bitstreams: 1 Atila dos Santos Batista. Papel dos receptores....pdf: 4517971 bytes, checksum: 2d9cb0d434dcb66027ca90861bbd1a75 (MD5) Previous issue date: 2012 / Fundação Oswaldo Cruz. Centro de Pesquisas Gonçalo Moniz. Salvador, Bahia, Brasil / Diferentes áreas do sistema nervoso central que participam da regulação cardiovascular recebem projeções de núcleos da rafe produtores de 5-HT. Diversos estudos têm também demonstrado a participação dos receptores serotoninérgicos nas respostas neuroendócrinas e emocionais ao estresse e no equilíbrio hidrossalino, assim os objetivos do referido trabalho foram: a) estudar o papel dos receptores do tipo 5-HT3 presentes na ASM (área septal medial) sobre as respostas cardiovasculares ao estresse de contenção em ratos; b) verificar a possível interação entre os receptores colinérgicos muscarínicos e 5-HT3 presentes na ASM no controle cardiovascular; c) verificar o papel dos receptores do tipo 5-HT3 na ASM sobre o controle hidrossalino. Foram utilizados ratos Wistar (280-300g) submetidos ao implante de uma cânula guia na ASM. Os animais destinados aos estudos cardiovasculares receberam implante de catéter carotídeo para análise da PA. No momento do experimento referente ao estresse os animais receberam injeção de m-CPBG e ondansetrona na ASM e 15 min após a microinjeção foram submetidos ao estresse de contenção com registro da PA. Para análise da interação entre os receptores muscarínicos e os receptores serotoninérgicos do tipo 5-HT3 os animais receberam previamente atropina, antagonista colinérgico muscarínico, e após 10 min receberam ondansetrona com registro constante da PA por mais 110min. No protocolo experimental para depleção de sódio os animais receberam microinjeções de furosemida 24h antes do experimento tendo disponíveis bebedouros de água destilada. No momento do experimento os animais receberam microinjeções de m-CPBG e ondansetrona e após 15 min os volumes de água e salina 1,5% foram registrados por 2h. Para análise do efeito do bloqueio dos receptores 5-HT3 sobre o comportamento de ingestão de água os animais foram submetidos a privação hídrica por 24h. No momento do experimento microinjeções de salina, m-CPBG ondansetrona foram feitas na ASM com medida dos volumes ingeridos ao longo de 2h. Verificamos que os receptores serotoninérgicos do tipo 5-HT3 presentes na ASM inibem o aumento da PA em animais submetidos ao estresse, além disso, verificamos também que a resposta hipertensiva decorrente do bloqueio dos receptores serotoninérgicos do tipo 5- HT3 depende da integridade funcional dos receptores colinérgicos muscarínicos. Por outro lado, tanto a ativação, quanto o bloqueio dos receptores serotoninérgicos do tipo 5-HT3 presentes na ASM parecem não mediar a ingestão de sódio em animais sódio-depletados nem a ingestão de água em animais sob privação hídrica. / Different areas of the central nervous system that participate in cardiovascular regulation receive the projections of rafe nuclei that product 5-HT. Several studies have also demonstrated the participation of serotoninergic receptors in neuroendocrine and emotional responses for stress and in fluid and electrolyte balance. Thus, the objectives of this work were: a) to study the role of type 5-HT3 receptors present in MSA (medial septal area) on the cardiovascular responses to stress of restraint in rats; b) to verify the possible interaction between muscarinic cholinergic receptors and 5-HT3 present in MSA in cardiovascular control; c) to verify the role of type 5-HT3 receptors in MSA on fluid and electrolyte control. There were used Wistar rats (280-300g) submitted to a guide cannula implant in MSA. The animals for cardiovascular studies received carotid catheter implant to AP analyses. At the time of stress experiment the animals received m-CPBG and ondansetron injection in MSA and, 15 minutes after microinjection were submitted to stress of restraint with the AP register. To analyses the interaction between the muscarinic receptors and 5-HT3 serotoninergic receptors, the animals previously received atropine, cholinergic muscarinic antagonist, and 10 minutes after received ondansetron with the constant register of AP for 110 minutes more. In the experimental protocol for sodium depletion animals received furosemide microinjections 24 hours before the experiment with distilled water drinking fountains available. At the time of the experiment the animals received m-CPBG and ondansetron injection and after 15 minutes the volumes of water and 1,5% saline were registered for two hours. To analyses the effect of 5-HT3 receptors blockade on the water ingestion behavior the animals had been submitted to water privation by 24 hours. At the time of the experiment microinjections of saline, m-CPBG and ondansetron were made in MSA with measurement of ingested volumes during two hours. We verified that the type 5-HT3 serotoninergic receptors present in MSA inhibit the increase of AP in animals on stress. In addition, we also verified that the hypertensive response due to the type 5-HT3 serotoninergic receptors blockade depends on the functional integrity of the muscarinic cholinergic receptors. On the other hand, both the activation as the blocking of type 5-HT3 serotoninergic receptors presents in MSA seem not to mediate sodium ingest in sodium-depleted animals nor the water ingestion in animals on water deprivation.