Angiotensin and baroreflex control of the circulation

Abstract

There is a close association between the location of angiotensin (Ang) receptors and many important brain nuclei involved in the regulation of the cardiovascular system. The present review encompasses the physiological role of Ang II in the brainstem, particularly in relation to its influence on baroreflex control of the heart and kidney. Activation of AT 1 receptors in the brainstem by fourth ventricle (4V) administration to conscious rabbits or local administration of Ang II into the rostral ventrolateral medulla (RVLM) of anesthetized rabbits acutely increases renal sympathetic nerve activity (RSNA) and RSNA baroreflex responses. Administration of the Ang antagonist Sarile into the RVLM of anesthetized rabbits blocked the effects of Ang II on the RSNA baroreflex, indicating that the RVLM is the major site of sympathoexcitatory action of Ang II given into the cerebrospinal fluid surrounding the brainstem. However, in conscious animals, blockade of endogenous Ang receptors in the brainstem by the 4V AT 1 receptor antagonist losartan resulted in sympathoexcitation, suggesting an overall greater activity of endogenous Ang II within the sympathoinhibitory pathways. However, the RSNA response to airjet stress in conscious rabbits was markedly attenuated. While we found no effect of acute central Ang on heart rate baroreflexes, chronic 4V infusion inhibited the baroreflex and chronic losartan increased baroreflex gain. Thus, brainstem Ang II acutely alters sympathetic responses to specific afferent inputs thus forming part of a potentially important mechanism for the integration of autonomic response patterns. The sympathoexcitatory AT 1 receptors appear to be activated during stress, surgery and anesthesia.

Phytochemical and in vitro and in vivo biological investigation on the antihypertensive activity of mango leaves (Mangifera indica L.)

“…Head and colleagues [Head et al 2002] showed the inverse relationship between the physiological function of the baroreflex and levels of angiotensin II (Ang II), and this fact is in agreement with our results where animals treated with dichloromethanic fraction of M. indica normalized their baroreflex sensitivity. This improvement may be related to observed inhibition of ACE and reduction of MAP.…”

Baroreflex modulation by angiotensins at the rat rostral and caudal ventrolateral medulla

“…Two groups of cardiovascular neurons have been functionally defined in the CVLM: neurons that relay baroreflex inputs from the NTS to the RVLM and neurons that are insensitive to the baroreflex input (14, 44). In addition, the CVLM depressor response, in part, is associated with vagally mediated decrease in heart rate (HR), suggesting a reciprocal connection between the main area containing parasympathetic preganglionic neurons, i.e., the nucleus ambiguus (NA), and the CVLM (47).Among the neurotransmitters and neuromodulators that participate in the control of blood pressure at brain stem areas, growing attention has been given to the peptides of the reninangiotensin system (RAS) (4,21,31,45). High concentrations of the AT 1 receptor and fibers with ANG II immunoreactivity have been described in the dorsomedial and ventrolateral areas of the medulla (2, 4, 21, 22).…”

“…Among the neurotransmitters and neuromodulators that participate in the control of blood pressure at brain stem areas, growing attention has been given to the peptides of the reninangiotensin system (RAS) (4,21,31,45). High concentrations of the AT 1 receptor and fibers with ANG II immunoreactivity have been described in the dorsomedial and ventrolateral areas of the medulla (2, 4, 21, 22).…”

“…High concentrations of the AT 1 receptor and fibers with ANG II immunoreactivity have been described in the dorsomedial and ventrolateral areas of the medulla (2,4,21,22). In addition, important interactions between angiotensinergic peptides and the neuronal elements of the VLM have been shown (47).…”

MicroRNA network changes in the brain stem underlie the development of hypertension

“…NTS contains the highest amount of ANG II receptors in the medulla, and this is evolutionarily conserved (4,14,23,30). RVLM also contains a high amount of ANG II receptors compared with the rest of the medulla (22,23). miR-135a putative mediation of ANG II signaling occurs via downregulation of Agtrap, angiotensin II receptor-associated mRNA.…”