Water deprivation increases angiotensin-converting enzyme but not AT1 receptor expression in brainstem and paraventricular nucleus of the hypothalamus of the rat

The authors investigated whether water deprivation in normotensive rats produce an upregulation of the central renin-angiotensin system in the areas of the brain that are involved in blood pressure control especially PVH and RVLM. They measured AT1 receptor expression in a number of regions in the brain using quantitative AT1 receptor autoradiography.  Similarly angiotensin converting enzyme (ACE) was also measured in the some of these regions using a similar technique. They found that ACE expression was increased in brain regions that are important for blood pressure control. However there was no difference in AT1 receptor expression in the brain regions tested between dehydrated rats and water-replete controls except in subfornical organ (SFO), a circumventricular lacking blood brain barrier. This study partially proves that during dehydration the central RAS could maintain blood pressure through increasing the expression of ACE. Similarly increased AT1 receptors in the SFO indicate an increased response to Ang II, because of the lack of blood brain barrier in the SFO. SFO sends excitatory projections to the PVN. The neurons form the PVN projects to RVLM, which then projects to the intermediolateral cell column of the spinal cord to activate the preganglionic neurons of the sympathetic nervous system.  The authors believe during water deprivation, the above mentioned pathway could be involved in the maintenance of normal blood pressure.  

-Madhan