Autonomic nervous system tissue effects

SYMPATHOMIMETIC AGENTS mimic the actions of the sympathetic division of the autonomic nervous system. The effects of this system on the tissues and organs are mediated by adrenaline and noradrenaline - which act predominantly as hormone or neurotransmitter, respectively. These catecholamines act at one of two receptor types, a-adrenoceptor and P-adrenoceptor, to exert the actions of the system. Sympathomimetics are of two types. 

The autonomic nervous system (ANS) modifies contractile activity of both types of smooth muscle. As discussed in Chapter 9, the ANS innervates the smooth muscle layer in a very diffuse manner, so neurotransmitter is released over a wide area of muscle. Typically, the effects of sympathetic and parasympathetic stimulation in a given tissue oppose each other one system enhances contractile activity while the other inhibits it. The specific effects (excitatory or inhibitory) that the two divisions of the ANS have on a given smooth muscle depend upon its location. 

While the dose-limiting toxicity for vinblastine usually is leukopenia, that for vincristine is most commonly neurotoxicity (58). Prominent manifestations of neurotoxicity are loss of the Achilles tendon reflex, paresthesias, loss of muscle strength (e.g., in the foot and wrist), and ataxia. Constipation and abdominal pain may occur and are thought to result, at least in part, from actions on the autonomic nervous system. Leukopenia and stomatitis are possible effects of vincristine treatment, but they occur relatively infrequently. Alopecia occurs with vincristine at a frequency comparable to that observed with vinblastine, and vincristine also is a potent tissue irritant. Vincristine may produce a syndrome of inappropriate secretion of antidiuretic hormone, and some manifestations of neurotoxicity, such as seizures, have been considered to be due to electrolyte disturbances associated with the relative excess of the antidiuretic hormone (58). 

CRITICAL ASSESSEMENT OF THE METHOD In general pharmacological studies during anesthesia should be assessed appropriately due to the possible interaction between the test compound and the used anesthetic as well as due to the reduced tone of the autonomic nervous system. Enteral administration of the candidate compound should be avoided, because enteral absorption of the test compound might be reduced due to the impaired intestinal motility during anesthesia. With respect to the effect of the aesthetic compound itself on intermediary metabolism the barbiturate pentobarbital sodium is the most inert anesthetic and does not cause alterations of metabolic blood and tissue parameters. In contrast, e.g. urethane as well as isoflurane (inhalation aesthetic) influences by itself substantially metabolic parameters over time (hours). 

Early studies of the parasympathetic nervous system showed that the alkaloid muscarine mimicked the effects of parasympathetic nerve discharge that is, the effects were parasympathomimetic. Application of muscarine to ganglia and to autonomic effector tissues (smooth muscle, heart, exocrine glands) showed that the parasympathomimetic action... 

Peptides are used by most tissues for cell-to-cell communication. As noted in Chapters 6 and 21, they play important roles in the autonomic and central nervous systems. Several peptides exert important direct effects on vascular and other smooth muscles. These peptides include vasoconstrictors (angiotensin II, vasopressin, endothelins, neuropeptide Y, and urotensin) and vasodilators (bradykinin and related kinins, natriuretic peptides, vasoactive intestinal peptide, substance P, neurotensin, calcitonin gene-related peptide, and adrenomedullin). This chapter focuses on the smooth muscle actions of the peptides. 

The prostaglandins and thromboxanes have major effects on four types of smooth muscle airway, gastrointestinal, reproductive, and vascular. Other important targets include platelets and monocytes, kidneys, the central nervous system, autonomic presynaptic nerve terminals, sensory nerve endings, endocrine organs, adipose tissue, and the eye (the effects on the eye may involve smooth muscle). 

The activation of the stress systems affects all tissues of the organism, and the peripheral immune system is no exception. These effects are mediated through at least tw o pathways via the HPA axis and by virtue of the innervation of lymphatic tissues by autonomic nerve fibers, especially from the sympathetic nervous system. All lymphoid tissues, primary (bone marrow and thymus) as well as secondary (spleen, lymph nodes, and gut-associated lymphoid tissue) are innervated by sympathetic nerve fibers. As discussed above, most lymphoid cells express catecholamine receptors, including B-lymphocytes, CD4- and CD 8-positive T cells, dendritic cells, monocytes, and macrophages. 

---