Role of the locus coeruleus on blood pressure response and atrial natriuretic peptide secretion following extracellular volume expansion

Extracellular volume expansion (EVE) was performed in intact rats and 24 h after locus coeruleus (LC) lesions or sham-operation. Blood pressure was re gistered 5 min before and after EVE. At the end of the experiment the anima ls were decapitated and blood was collected from the trunk for quantificati on of plasma atrial natriuretic peptide (ANP). All experimental groups show ed 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 ant erior region of the LC. There was no pronounced c-fos expression in any reg ion of the LC 2 h after EVE in intact animals. in conclusion, the data supp ort 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 a re necessary during changes in blood volume. The results on c-fos expressio n are in accordance with the idea that this nucleus may be part of an inhib itory pathway which modulates the circuits of control for depressor reflex response and ANP secretion after extracellular volume expansion. (C) 1999 E lsevier Science Inc.