RESUMEN
Extracellular volume expansion (EVE) was performed in intact rats and 24 h after locus coeruleus (LC) lesions or sham-operation. Blood pressure was registered 5 min before and after EVE. At the end of the experiment the animals were decapitated and blood was collected from the trunk for quantification of plasma atrial natriuretic peptide (ANP). All experimental groups showed similar basal blood pressure. Volume expansion caused a slight decrease in blood pressure and an increase in ANP secretion in all groups, but these changes were significantly enhanced in animals bearing a lesion in the anterior region of the LC. There was no pronounced c-fos expression in any region of the LC 2 h after EVE in intact animals. In conclusion, the data support the idea that the LC does not participate in blood pressure control in resting conditions. However, the anterior region of the LC seems to play a role when adjustments of blood pressure and excretion of water and sodium are necessary during changes in blood volume. The results on c-fos expression are in accordance with the idea that this nucleus may be part of an inhibitory pathway which modulates the circuits of control for depressor reflex response and ANP secretion after extracellular volume expansion.
Asunto(s)
Factor Natriurético Atrial/sangre , Presión Sanguínea/fisiología , Locus Coeruleus/fisiología , Animales , Factor Natriurético Atrial/metabolismo , Volumen Sanguíneo/fisiología , Espacio Extracelular/fisiología , Masculino , Proteínas Proto-Oncogénicas c-fos/análisis , Proteínas Proto-Oncogénicas c-fos/biosíntesis , Ratas , Ratas Wistar , Valores de ReferenciaRESUMEN
Bilateral electrolytic lesions in the rat Locus Coeruleus (LC) were made one or seven days before experimentation. Four hemorrhage sessions, withdrawing 10% of the blood volume per session, were performed in 5 min intervals in freely moving rats. Blood pressure (BP) was not affected by the lesions and did not drop in the first, but decreased in all subsequent hemorrhages. The decrease in BP in animals with lesion in the anterior LC was similar to the controls. However, animals with lesions in the posterior LC showed an enhanced decrease in BP during the second hemorrhage, in acute and chronic experiments. Expression of Fos protein was studied to investigate the relationship between LC activity and BP changes. Two hours after the second hemorrhage, the brains were removed and processed for Fos immunocytochemistry. Hemorrhage increased the number of Fos immunoreactive neurons mainly in the posterior LC. We conclude that (1) the LC does may not play a role in cardiovascular control during resting, but seems to mediate compensatory cardiovascular mechanisms in situations of hypovolemia; and (2) the posterior LC, but not the anterior, plays a pressor role during hemorrhage.