Cardiovascular actions of microinjections of angiotensin II in the brain stem of rats

Casto, R. Michael; Phillips, M. Ian

doi:10.1152/ajpregu.1984.246.5.r811

Cited by 45 publications

(35 citation statements)

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“…Norepinephrine, acetylcholine, epinephrine, Lglutamate, dopamjne, and other agents are known to reduce blood pressure and heart rate when injected into the NTS. In contrast, certain agents, such as angiotensin II, 26 vasopressin, 27 and yohimbine, 28 have been shown to raise blood pressure and heart rate when injected into this site.…”

Section: Discussionmentioning

confidence: 94%

Purinergic receptors in the brainstem mediate hypotension and bradycardia.

et al. 1988

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SUMMARY Adenosine acts at many sites to modulate neuronal activity. The purpose of this study was to investigate a possible role for adenosine as a neuromodnlator of brainstem cardiovascular control. Microinjections of adenosine (0-2.3 nmol) were made stereotaxically into various brainstem sites. Injection of adenosine into the nucleus tractus solitarii (NTS) produced dose-related decreases in heart rate and systolic and diastolic blood pressures. Maximal changes occurred 90 seconds after injection. Injection into the area postrema also produced decreased heart rate and systolic and diastolic blood pressures. No significant effect occurred following injection into the Cl area. Adenosine 5-triphosphate and its analogue, /3,-y-methylene adenosine 5-triphosphate also produced doserelated and potent vasodepressor and bradycardia effects in the NTS. Injection of l,3-dipropyl-8-psulfophenylxanthine (0.92 nmol), a potent adenosine receptor antagonist, produced no effect itself, but abolished for 45 minutes the actions of further injections of adenosine and adenosine 5'-triphosphate (but not L-glutamate) in both the NTS and area postrema. Thus, NTS and area postrema injections of adenosine decrease blood pressure and heart rate in anesthetized normotensive rats through adenosine receptors located in these areas. These findings support a role for endogenous adenosine as a central modulator in cardiovascular control. (Hypertension 11: 191-197, 1988) KEY WORDS • adenosine • adenosine 5'-triphosphate • central nervous system • nucleus tractus solitarii • area postrema • rats • nucleosides • purines • purinergic neurotransmission A UTONOMIC cardiovascular control is achieved / \ in the medulla oblongata through integration X \ . of input from higher centers with afferent input from receptors in chest and neck structures.1 This afferent input travels in the vagus and glossopharyngeal nerves and terminates principally in the nucleus tractus solitarii (NTS). NTS neurons have projections to many rostral and ventral sites. The Cl area in the ventrolateral medulla, which contributes to the tonic control over sympathetic outflow, receives some of these NTS projections.2 Stimulation of the NTS produces inhibition of sympathetic tone, while stimulation of the Cl area leads to an increase in sympathetic activation.

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Section: Discussionmentioning

confidence: 94%

Purinergic receptors in the brainstem mediate hypotension and bradycardia.

et al. 1988

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“…Thus, it is not surprising that this nucleus has been suggested as a main region for Ang influencing baroreceptor afferent information (8,54) as well as the integration of chemoreceptor afferents (54). In anesthetized rats, microinjection of Ang into the NTS produces pressor responses at nmol doses (55) and depressor responses at pmol doses (56), and attenuates the baroreceptor reflex (57,58) through AT 1 receptors. Our own studies in anesthetized rabbits are consistent with these findings since we observed mainly depressor responses to 1 pmol Ang II injected into the dorsomedial region.…”

Section: Ang Actions Within the Nucleus Tractus Solitariusmentioning

confidence: 99%

Angiotensin and baroreflex control of the circulation

Head¹,

Saigusa

Mayorov³

2002

Braz J Med Biol Res

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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.

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“…81 Microinjection of Ang II into the nucleus of the solitary tract produces depressor (low-dose) and pressor responses. 82,83 The pressor response involves activation of sympathetic efferent pathways. The rostral ventrolateral medulla contains a population of sympathetic premotor neurons whose tonic activity is essential for the maintenance of sympathetic vasomotor tone and normal resting BP.…”

Section: Sympathetic Nerve Activitymentioning

confidence: 99%