Sympathetic nervous system regulation

Hinojosa-Laborde C, Chapa I, Lange D, Haywood JR. Gender differences in sympathetic nervous system regulation. Clin Exp Pharmacol Physiol 1999 26 122-126. 

The part of the vertebrate nervous system that regulates involuntary action, such as the intestines, heart and glands it is divided into the sympathetic nervous system and the parasympathetic nervous system. 

The regulation of the total peripheral resistance also involves the complex interactions of several mechanisms. These include baroreflexes and sympathetic nervous system activity response to neurohumoral substances and endothelial factors myogenic adjustments at the cellular level, some mediated by ion channels and events at the cellular membrane and intercellular events mediated by receptors and mechanisms for signal transduction. As examples of some of these mechanisms, there are two major neural reflex arcs (Fig. 1). Baroreflexes are derived from high-pressure barorecep-tors in the aortic arch and carotid sinus and low-pressure cardiopulmonary baroreceptors in ventricles and atria. These receptors respond to stretch (high pressure) or... 

The adrenal gland is located on the upper segment of the kidney (Fig. 42-1). It consists of an outer cortex and an inner medulla. The adrenal medulla secretes the catecholamines epinephrine (also called adrenaline) and norepineprhine (also called noradrenaline), which are involved in regulation of the sympathetic nervous system. The adrenal cortex consists of three histologically distinct zones zona glomerulosa, zona fasciculata, and an innermost layer called the zona reticularis. Each zone is responsible for production of different hormones (Fig. 42-2). 

Figure 15.5 Effects of sympathetic and parasympathetic nervous activity on mean arterial pressure. The parasympathetic nervous system innervates the heart and therefore influences heart rate and cardiac output. The sympathetic nervous system innervates the heart and veins and thus influences cardiac output. This system also innervates the arterioles and therefore influences total peripheral resistance. The resulting changes in cardiac output and total peripheral resistance regulate mean arterial pressure.

Loss of plasma volume leads to a decrease in MAP. Baroreceptors located in the aortic and carotid sinuses detect this fall in MAP and elicit reflex responses that include an increase in the overall activity of the sympathetic nervous system. Sympathetic stimulation of the heart and blood vessels leads to an increase in cardiac output (CO) and increased total peripheral resistance (TPR). These adjustments, which increase MAP, are responsible for the short-term regulation of blood pressure. Although increases in CO and TPR are effective in temporary maintenance of MAP and blood flow to the vital organs, these activities cannot persist indefinitely. Ultimately, plasma volume must be returned to normal (see Table 19.1). 

Altman, J. D., Trendelenburg, A. U., MacMillan, L. etal. Abnormal regulation of the sympathetic nervous system in alpha2A-adrenergic receptor knockout mice. Mol. Pharmacol. 56 154-161,1999. 

Another clinically important effect I would like to mention is the inhibition of salivary secretion by clonidine. Both the sympathetic nervous system and the parasympathetic nervous system are involved in the physiological regulation of salivation. HOEFKE (53) as well as RAND and coworkers (54) found that parasympathetic salivary secretion stimulated by electrical impulses on the chorda tympani and by carbachol could not be blocked by clonidine in anaesthetised animals. In our own experiments in rats with clonidine and the 2,6-diethyl derivative St 91 which does not penetrate to the CNS, secretion of saliva was blocked only after clonidine, (HOEFKE (55)) indicating a central mode of action. 

The sympathetic nervous system plays an important role in the involuntary regulation of cardiac activity, vascular tonicity, functional activity of smooth muscle, and glands by releasing endogenic adrenergic substances, cateeholines, from peripheral nerve endings into the synapses of the central nervous system (CNS). 

Abrupt interruption of propranolol therapy in individuals with angina pectoris has been associated with reappearance of angina, acute myocardial infarction, or death due to a sudden increase in sympathetic nervous system tone to the heart. The mechanisms underlying these reactions are unknown, but they may be the result of an increase in the number of p-receptors that occur following chronic p-adrenoceptor blockade (up-regulation of receptors). When it is advisable to discontinue propranolol administration, such as before coronary bypass surgery, the dosage should be tapered over 2 to 3 days. 

The sympathetic nervous system is an important regulator of virtually all organ systems. This is particularly evident in the regulation of blood pressure. As illustrated in the case study, the autonomic nervous system is crucial for the maintenance of blood pressure even under relatively minor situations of stress (eg, the gravitational stress of standing). 

N.A. Rauvolfia serpentina (L.) Benth. Indole alkaloids, reserpine, rescinnamine, ajmaline, yohimbine.99 Regulate hearbeat, treat high blood pressure and anxiety. Sedative and depressant effect on sympathetic nervous system. 

Altman JD, Trendelenburg AU, MacMillan L, Bernstein D, Limbird L, Starke K, Kobilka BK, Hein L (1999) Abnormal regulation of the sympathetic nervous system in 2a-adrenergic receptor knockout mice. Mol Pharmacol 56 154-61 Anagnostaras SG, Murphy GG, Hamilton SE, Mitchell SL, RahnamaNP, Nathanson NM, Silva A1 (2003) Selective cognitive dysfunction in acetylcholine Mi muscarinic receptor mutant mice. Nature Neurosd 6 51-8... 

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