Involvement of Renal Sympathetic Nerve in Pathogenesis of Hypertension

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Hiroo Kumagai, Toshiko Onami, Kamon Iigaya, Chie Takimoto, Masaki Imai, Tomokazu Matsuura, Katsufumi Sakata, Naoki Oshima, Koichi Hayashi, Takao Saruta

Department of Internal Medicine, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan

Network of the Sympathetic Nervous System and Baroreflex

Figure 1 demonstrates the network of the sympathetic nervous system (SNS) [1-8]. The rostral ventrolateral medulla (RVLM, shaded area) contains neurons that stimulate the SNS and determine blood pressure (BP). If electrophysiological activity of the RVLM bulbospinal neurons is increased, it activates peripheral sympathetic nerves to the heart, the kidney (renal sympathetic nerve activity, RSNA), and arterioles, thus elevating BP. Figure 1 also illustrates the arterial baroreflex that makes BP stable. The baroreflex is a negative feedback system. When BP is elevated, activities of arterial baroreceptors at carotid sinus and vagal afferent nerves (IXth and Xth cranial nerves) are increased, and neuronal activity of the caudal VLM (CVLM) is increased via the nucleus tractus solitarius (NTS). Since synaptic transmission from CVLM neurons to the RVLM is mediated by an inhibitory amino acid (7-amino butyric acid, GABA) [1, 2], the neuronal activity of the RVLM is suppressed, and efferent sympathetic nerves (such as RSNA) and BP are decreased to the original level.

Conversely, if BP is reduced by standing or antihypertensive drugs, the activities of vagal afferents, the NTS, and CVLM neurons are reduced. Then, the activity of RVLM neurons is increased, and efferent sympathetic nerve activities should be activated. Thus, BP is increased to the original level.

Neuron Renal

Fig. 1. The SNS and arterial baroreceptor reflex. RVLM (shaded area) = rostral ventrolateral medulla; CVLM = caudal ventrolateral medulla; GABA = 7-amino butyric acid; NTS = nucleus tractus solitarius. Activated RVLM neuron increases peripheral sympathetic nerves to the heart, kidney, and arterioles, thus inducing hypertension.

Fig. 1. The SNS and arterial baroreceptor reflex. RVLM (shaded area) = rostral ventrolateral medulla; CVLM = caudal ventrolateral medulla; GABA = 7-amino butyric acid; NTS = nucleus tractus solitarius. Activated RVLM neuron increases peripheral sympathetic nerves to the heart, kidney, and arterioles, thus inducing hypertension.

The arterial baroreflex mentioned above is the so-called high-pressure baroreflex. The cardiopulmonary baroreflex (low-pressure baroreflex) is also important to maintain sodium and water balance. When circulating plasma volume increases, that is, sodium and water balance is positive, this signal stimulates left atria receptors. This information decreases RSNA via vagal afferent-mediated projections to the RVLM. The decreased RSNA increases sodium excretion. Conversely, when circulating plasma volume is decreased, RSNA increases to

Renal Sympathetic Nerve Hypertension

♦ Hypertension

Fig. 2. Functional roles of renal sympathetic nerve in the initiation of hypertension. JGA = juxtaglomerular apparatus; RVLM = rostral ventrolateral medulla. Increased renal sympathetic nerve activity (RSNA) produces renin release (then genesis of angiotensin II, Ang II), sodium reabsorption, and reduction in renal blood flow, thus inducing hypertension.

♦ Hypertension

Vasoconstriction -

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