Mecanismos centrais e periféricos na regulação do fluxo sanguíneo muscular
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Data
1997
Autores
Pôssas, Olga Sueli [UNIFESP]
Orientadores
Cravo, Sérgio Luiz Domingues [UNIFESP]
Tipo
Tese de doutorado
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Resumo
A manutencao de um fluxo sanguineo adequado e essencial para a homeostase do organismo. Ajustes rapidos e diferenciados do debito cardiaco aos diversos territorios vasculares sao obtidos atraves de uma complexa rede neural cuja principal via eferente e a divisao simpatica do sistema nervoso vegetativo. A organizacao central desta rede assim como seus mecanismos perifericos permanecem, em grande parte, desconhecidos. Na medula oblonga, o nucleo rostroventrolateral (RVL) e o responsavel pela manutencao do tono vasomotor e constitui a via eferente comum dos ajustes cardiovasculares provocados pela estimulacao de aferentes dos baroceptores, quimioceptores e aferentes somaticos e viscerais. O presente trabalho contem dois estudos em que buscamos determinar: I. o papel do RVL nos ajustes cardiovasculares produzidos pela estimulacao de aferentes somaticos; II. a participacao do oxido nitrico (NO) nos ajustes hemodinamicos produzidos pela estimulacao de aferentes do nervo laringeo superior (NLS) e do nervo aortico depressor (NAD). Na primeira parte desse estudo utilizamos ratos Wistar machos (280-350 g, N = 32) anestesiados com uretana (1,2 g/kg, i.p.), paralisados (d-tubocurarina, 0,5 mg/kg, i.v.) e ventilados artificialmente. Aferentes somaticos do nervo ciatico foram estimulados eletricamente com pulsos quadrados de 1 ms de duracao, 50 Hz de frequencia, de 800 a 1000 µA de intensidade por 10 s. A arteria carotida e a veia jugular foram cateterizadas para registro de pressao arterial (PA) e frequencia cardiaca (FC) e infusao de drogas respectivamente. O fluxo sanguineo (FS) do membro estimulado foi registrado por fluxometria Doppler, atraves de sondas miniaturizadas implantadas na arteria iliaca e expresso como a variacao percentual do valor basal. A condutancia vascular (CV) foi calculada como a razao entre as variacoes de FS e PA e tambem expressa como a variacao percentual. Os resultados obtidos demonstraram que: 1. a estimulacao eletrica do ciatico produziu hipertensao, taquicardia e vasodilatacao no membro estimulado; 2. a administracao sistemica de atropina (3mg/kg, i.v.) ou propranolol (4 mg/kg, i.v.) nao modificaram a resposta pressora ou a resposta vasodilatadora, mas diminuiram a resposta taquicardica; 3. microinjecao unilateral do agente neuroexcitatorio/neurotoxico acido cainico (2 nmol/100 nL) no RVL, contralateral ao nervo estimulado aboliu os ajustes cardiovasculares a estimulacao do ciatico; 4. a microinjecao do antagonista glutamatergico, acido quinurenico (2 nmol/ 100 nL) no RVL contralateral, aboliu a resposta pressora e a taquicardia, porem, nao modificou o aumento de FS o que resultou em um aumento da resposta vasodilatadora; 5. a microinjecao do antagonista GABAergico, bicuculina (0,4 nmol/100 nL), nao modificou a resposta pressora, porem aboliu o aumento de FS, observando-se portanto vasoconstricao em resposta a estimulacao do ciatico. Os resultados obtidos demonstram que o nucleo RVL contralatareal ao membro estimulado representa a via eferente dos ajustes cardiovasculares provocados pela estimulacao de aferentes somaticos. A vasodilatacao observada nao depende da ativacao de fibras vasodilatadoras colinergicas ou a de receptores β-adrenergicos. No RVL aferencias glutamatergicas parecem ser responsaveis pela resposta pressora, enquanto aferentes GABAergicos parecem estar envolvidos com a vasodilatacao produzida pela estimulacao de aferentes somaticos. Na segunda parte desse estudo utilizamos ratos Wistar machos (250 - 350 g, N = 46) anestesiados (pentobarbital, 50 mg/kg, i.v.), traqueostomizados e respirando espontaneamente. A arteria e veia femoral foram caracterizadas para registro de PA, FC e infusao de drogas respectivamente. O NLS e o NAD foram dissecados e estimulados eletricamente (pulsos quadrados de 0,5 ms; 1 a 10 Hz; 8 V, durante 15 s) com intervalo de 10 min entre cada estimulacao. Em alguns experimentos a cadeia simpatica lombar (CSL) foi dissecada e o seu ramo esquerdo eletricamente estimulado (pulsos quadrados de 0,5 ms; 2,5 - 4 V; 20 Hz) com intervalo de 10 min. O fluxo sanguineo mesenterico (FSM); do trem posterior (FSTP) ou do membro posterior esquerdo (FSI) foram registrados por fluxometria Doppler atraves de sondas implantadas na arteria mesenterica, aorta abdominal ou arteria iliaca. A resistencia vascular foi calculada como a razao entre os picos maximos de variacao da PA e do FS ou foi calculada em alguns casos, como a razao entre a variacao total de PA e de FS durante o periodo de estimulacao. Nossos resultados demonstraram que: 1. a estimulacao eletrica (EE) da CSL produziu discreta hipotensao e uma reducao acentuada da resistencia vascular ipsilateral, indicando vasodilatacao ativa; 2. a administracao sistemica de um bloqueador especifico da NO sintase neuronal, o 7-nitroindazol (7-NI, 45 mg/kg, i.v.) aboliu a vasodilatacao produzida pela estimulacao da CSL; 3. a EE do NLS ou do NAD produziu hipotensao, vasodilatacao mesenterica e do trem posterior dependentes de frequencia ; 4. a administracao sistemica de L-NAME (50 µmol/kg, i.v.), um inibidor das formas endotelial e neuronal de NO sintase aboliu a hipotensao, a vasodilatacao mesenterica e a vasodilatacao do trem posterior, enquanto o 7-NI aboliu apenas a vasodilatacao do trem posterior sem interferir com a vasodilatacao mesenterica; 5. a vasodilatacao do trem posterior produzida pelas estimulacoes com frequencia de 10 Hz nao foram diferentes no primeiro episodio de EE apos o 7-NI, porem, diminuiram progressivamente com episodios sucessivos de EE. Esses resultados sugerem que, no rato, a estimulacao de aferentes do NLS e do NAD produz vasodilatacao no trem posterior que e mediada por NO liberado a partir de fibras nervosas da cadeia simpatica pos ganglionar
Body homeostasis depends on an appropriate blood flow. Rapid adjustments of the cardiac output to different vascular beds are produced by a complex neural network. The sympathetic division of the autonomic nervous system is the major efferent system for these adjustments. However its central organization as well the peripheral mechanisms involved are not completely established. Within medulla oblongata, the nucleus reticularis rostroventrolateralis (RVL) harbors the neurons responsible for maintenance of the vasomotor tone. Also, the RVL constitutes the efferent arm of cardiovascular adjustments produced by the stimulation of baroreceptor, chemoreceptor, somatic and visceral afferents. In the present study we investigated two components of these systems. We sought to determine: I. the role of the RVL in the cardiovascular adjustments produced by the stimulation of somatic afferent fibers; II. the role of nitric oxide (NO) as a neurotransmitter in the hemodynamic adjustments produced by stimulation of the superior laryngeal nerve (SLN) and the aortic depressor nerve (ADN) afferents. For the first study, male Wistar rats (250-350 g, N = 32) were anesthetized (urethane 1.2 g/kg, i.v.), paralyzed (d-tubocurarine, 0.5 mg/kg, i.v.) and artificially ventilated. Somatic afferent fibers of the sciatic nerve were electrically stimulated with (square pulses, 1 ms, 50 Hz, 800-1000 A, for 10 s). Catheters were placed into the carotid artery and jugular vein for measurement of mean arterial blood pressure (MAP), heart rate (HR) and drugs administration, respectively. The stimulated hindlimb blood flow (HLF) was recorded by Doppler flowmetry, by miniature probes placed in the iliac artery and was represented as the percentage of the baseline. Hindlimb relative vascular conductance (VC) was calculated by dividing Doppler shift (Hz) by the mean arterial pressure (mmHg) and also represented as percentage of basal levels. Results obtained demonstrated that: 1. electrical stimulation of the sciatic nerve produced hypertension, tachycardia and vasodilatation in the stimulated hindlimb; 2. systemic administration of atropine (3 mg/kg, i.v.) or propranolol (4 mg/kg, i.v.) did not modify the pressor or the vasodilator response, but tachycardia was reduced; 3. unilateral microinjections of the neuroexcitatory/neurotoxic agent (kainic acid, 2 nmol/100 nL) into the RVL contralateral to the stimulated limb abolished cardiovascular adjustments produced by sciatic stimulation; 4. after microinjection of the glutamatergic antagonist, kynurenic acid (2 nmol/100nL) into the contralateral RVL, MAP and HR responses were reduced whereas HBF responses were not modified, therefore, vasodilatatory responses were increased; 5. when the GABAergic antagonist, bicuculine (0.4 nmol/100 nL) was microinjected into the contralateral RVL, the pressor response was not modified, tachycardia was reversed to bradycardia and HBF response was abolished, hence VC decreased. These results demonstrated that the RVL represents the efferent arm of the cardiovascular adjustments produced by stimulation of somatic afferents. Within RVL glutamatergic afferents mediates pressor responses whilst GABAergic afferents modulates vasodilatatory responses. In the second study male Wistar rats (250-350 g) were anesthetized (pentobarbital, 50 mg/kg, i.v.), and the trachea was cannulated. The femoral artery and vein were catheterized for arterial blood pressure (AP) and heart rate (HR) recordings and infusing drugs, respectively. The superior laryngeal nerve (SLN) or the aortic depressor nerver (ADN) were dissected and electrically stimulated (square pulses of 0,5 ms; 1-10 Hz; 8 V, during 15 s) with 10 minutes between each stimulus. In some experiments the lumbar sympathetic chain (LSC) was isolated and its left branch was electrically stimulated (square waves of 0,5 ms; 2.5-4.0 V; 20 Hz) with 10 min. interval between each stimulus. The mesenteric blood flow (MBF); hindquarter blood flow (HQF) or the left hindlimb flow (HLF) were measured by pulsed Doppler flow probes placed on the mesenteric, abdominal aorta or on the iliac artery. The vascular resistance was calculated as the ratio between the maximal AP variation and blood flow (BF). In some experiments the vascular resistance was calculated as the total variation of AP and BF during the stimulation period. Our results demonstrated that: 1. the electrical stimulation (ES) of the LSC produced minor falls in AP and pronounced increases in HLF, which resulted in marked reductions on the ipsilateral hindlimb vascular resistance, 2. the vasodilatation produced by EE of the LSC was abolished following administration of 7-nitroindazole (7-NI, 45 mg/kg, i.v.), a specific inhibitor of neuronal NO-sintase; 3. EE of the SLN or the ADN produced decrease in PA, and frequency-dependent vasodilatation in the mesenteric and hindquarter (HQ) vascular beds; 4. the fall in AP and the mesenteric and HQ vasodilatation were abolished following the administration of L-NAME (50 mol/kg, i.v.), an inhibitor of both neuronal and endothelial NO-sintase. The prior administration of 7-NI abolished the HQ vasodilatation whereas the mesenteric vasodilatation was unaffected; 5. the HQ vasodilatation produced by EE with 10 Hz stimulation was not initially decreased following the 7-NI administration. However, upon repetitive EE the HQ vasodilatation progressively diminished such that only a minor vasodilatation was observed after 4 or 5 episodes EE. These results suggest that, in rats, the EE of the afferent fibers of the SLN and of the ADN produce HQ vasodilatation which is mediated by NO released from sympathetic post-ganglionic fibers of the lumbar sympathetic chain.
Body homeostasis depends on an appropriate blood flow. Rapid adjustments of the cardiac output to different vascular beds are produced by a complex neural network. The sympathetic division of the autonomic nervous system is the major efferent system for these adjustments. However its central organization as well the peripheral mechanisms involved are not completely established. Within medulla oblongata, the nucleus reticularis rostroventrolateralis (RVL) harbors the neurons responsible for maintenance of the vasomotor tone. Also, the RVL constitutes the efferent arm of cardiovascular adjustments produced by the stimulation of baroreceptor, chemoreceptor, somatic and visceral afferents. In the present study we investigated two components of these systems. We sought to determine: I. the role of the RVL in the cardiovascular adjustments produced by the stimulation of somatic afferent fibers; II. the role of nitric oxide (NO) as a neurotransmitter in the hemodynamic adjustments produced by stimulation of the superior laryngeal nerve (SLN) and the aortic depressor nerve (ADN) afferents. For the first study, male Wistar rats (250-350 g, N = 32) were anesthetized (urethane 1.2 g/kg, i.v.), paralyzed (d-tubocurarine, 0.5 mg/kg, i.v.) and artificially ventilated. Somatic afferent fibers of the sciatic nerve were electrically stimulated with (square pulses, 1 ms, 50 Hz, 800-1000 A, for 10 s). Catheters were placed into the carotid artery and jugular vein for measurement of mean arterial blood pressure (MAP), heart rate (HR) and drugs administration, respectively. The stimulated hindlimb blood flow (HLF) was recorded by Doppler flowmetry, by miniature probes placed in the iliac artery and was represented as the percentage of the baseline. Hindlimb relative vascular conductance (VC) was calculated by dividing Doppler shift (Hz) by the mean arterial pressure (mmHg) and also represented as percentage of basal levels. Results obtained demonstrated that: 1. electrical stimulation of the sciatic nerve produced hypertension, tachycardia and vasodilatation in the stimulated hindlimb; 2. systemic administration of atropine (3 mg/kg, i.v.) or propranolol (4 mg/kg, i.v.) did not modify the pressor or the vasodilator response, but tachycardia was reduced; 3. unilateral microinjections of the neuroexcitatory/neurotoxic agent (kainic acid, 2 nmol/100 nL) into the RVL contralateral to the stimulated limb abolished cardiovascular adjustments produced by sciatic stimulation; 4. after microinjection of the glutamatergic antagonist, kynurenic acid (2 nmol/100nL) into the contralateral RVL, MAP and HR responses were reduced whereas HBF responses were not modified, therefore, vasodilatatory responses were increased; 5. when the GABAergic antagonist, bicuculine (0.4 nmol/100 nL) was microinjected into the contralateral RVL, the pressor response was not modified, tachycardia was reversed to bradycardia and HBF response was abolished, hence VC decreased. These results demonstrated that the RVL represents the efferent arm of the cardiovascular adjustments produced by stimulation of somatic afferents. Within RVL glutamatergic afferents mediates pressor responses whilst GABAergic afferents modulates vasodilatatory responses. In the second study male Wistar rats (250-350 g) were anesthetized (pentobarbital, 50 mg/kg, i.v.), and the trachea was cannulated. The femoral artery and vein were catheterized for arterial blood pressure (AP) and heart rate (HR) recordings and infusing drugs, respectively. The superior laryngeal nerve (SLN) or the aortic depressor nerver (ADN) were dissected and electrically stimulated (square pulses of 0,5 ms; 1-10 Hz; 8 V, during 15 s) with 10 minutes between each stimulus. In some experiments the lumbar sympathetic chain (LSC) was isolated and its left branch was electrically stimulated (square waves of 0,5 ms; 2.5-4.0 V; 20 Hz) with 10 min. interval between each stimulus. The mesenteric blood flow (MBF); hindquarter blood flow (HQF) or the left hindlimb flow (HLF) were measured by pulsed Doppler flow probes placed on the mesenteric, abdominal aorta or on the iliac artery. The vascular resistance was calculated as the ratio between the maximal AP variation and blood flow (BF). In some experiments the vascular resistance was calculated as the total variation of AP and BF during the stimulation period. Our results demonstrated that: 1. the electrical stimulation (ES) of the LSC produced minor falls in AP and pronounced increases in HLF, which resulted in marked reductions on the ipsilateral hindlimb vascular resistance, 2. the vasodilatation produced by EE of the LSC was abolished following administration of 7-nitroindazole (7-NI, 45 mg/kg, i.v.), a specific inhibitor of neuronal NO-sintase; 3. EE of the SLN or the ADN produced decrease in PA, and frequency-dependent vasodilatation in the mesenteric and hindquarter (HQ) vascular beds; 4. the fall in AP and the mesenteric and HQ vasodilatation were abolished following the administration of L-NAME (50 mol/kg, i.v.), an inhibitor of both neuronal and endothelial NO-sintase. The prior administration of 7-NI abolished the HQ vasodilatation whereas the mesenteric vasodilatation was unaffected; 5. the HQ vasodilatation produced by EE with 10 Hz stimulation was not initially decreased following the 7-NI administration. However, upon repetitive EE the HQ vasodilatation progressively diminished such that only a minor vasodilatation was observed after 4 or 5 episodes EE. These results suggest that, in rats, the EE of the afferent fibers of the SLN and of the ADN produce HQ vasodilatation which is mediated by NO released from sympathetic post-ganglionic fibers of the lumbar sympathetic chain.
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Citação
PÔSSAS, Olga Sueli. Mecanismos centrais e periféricos na regulação do fluxo sanguíneo muscular. Tese (Doutorado em Ciências) - Escola Paulista de Medicina, Universidade Federal de São Paulo (UNIFESP), São Paulo, 1997.