Sympathetic ganglia blockade

Following intravenous injection in the mother, placental transfer of Metubine iodide occurs rapidly, and, after 6 minutes, the fetal plasma concentration is approximately one-tenth the maternal level. Metocurine does not inhibit vagal transmission or sympathetic ganglionic blockade, and therefore produces minimal hemodynamic changes in humans. The relatively stable heart rate and blood pressure associated with its use make it a useful agent for patients with coronary artery disease and hypertension. 

It acts as a potent parasympatholytic by blocking the nerve impulses at the site of parasympathetic ganglia however, it fails to invoke a sympathetic ganglionic blockade. It has been observed to be highly... 

The sympathetic nervous system, through hberation of norepinephrine in adipose tissue, plays a central role in the mobilization of free fatty acids. Thus, the increased hpolysis caused by many of the factors described above can be reduced or abolished by denervation of adipose tissue or by ganglionic blockade. 

TABLE 11-1 Predominance of sympathetic or parasympathetic tone at effector sites effects of autonomic ganglionic blockade... 

Depletion by guanidines, unlike depletion by reserpine, is not dependent on sympathetic innervation, and is unaffected by denervation of peripheral tissues [400], or by ganglionic blockade [264, 401]. The ability of some drugs to antagonize the depleting action of guanidines without appreciably reducing that of reserpine has been described earlier (p. 185). 

E. The effect of ganglionic blockade depends upon the predominant autonomic tone exerted within various organ systems. Since the activity of the parasympathetic nervous system predominates in the eye, the effect of ganglionic blockade is mydriasis, not miosis. Similarly, stimulation of the genital tract and urinary retention would be decreased. Since sympathetic nervous system activity predominates in blood vessels and the ventricles, vasodilation and a decreased cardiac output would follow ganglionic blockade. 

The ganglion-blocking drugs cause a predictable cycloplegia with loss of accommodation because the ciliary muscle receives innervation primarily from the parasympathetic nervous system. The effect on the pupil is not so easily predicted, since the iris receives both sympathetic innervation (mediating pupillary dilation) and parasympathetic innervation (mediating pupillary constriction). Ganglionic blockade often causes moderate dilation of the pupil because parasympathetic tone usually dominates this tissue. 

Blood vessels receive chiefly vasoconstrictor fibers from the sympathetic nervous system therefore, ganglionic blockade causes a marked decrease in arteriolar and venomotor tone. The blood pressure may fall precipitously because both peripheral vascular resistance and venous return are decreased (see Figure 6-7). Hypotension is especially marked in the upright position (orthostatic or postural hypotension), because postural reflexes that normally prevent venous pooling are blocked. 

Reserpine, Chlorpromazine and other Psycholeptic Drugs Reserpine depletes postganglionic sympathetic fibres of their noradrenaline and the peripheral sympathetic responses of animals which have been pretreated with reserpine are those which would be expected to follow loss of sympathetic transmitter . Thus, in adrenalectomized, reserpinized cats, stimulation of the splanchnic nerves does not produce the increase in blood pressure which is seen in non-reserpinized animals. Hexamethonium normally produces hypotension due to ganglionic blockade in the reserpinized animal it is without effect. Reserpine also causes a loss of adrenaline from the adrenal medulla. Since this adrenaline is liberated into the blood stream, it is not surprising that reserpine causes hyperglycaemia. 

Existing sympathetic tone is critical in determining the degree to which blood pressure is lowered by ganglionic blockade thus, blood pressure may be decreased only minimally in recumbent nor-motensive subjects but may fall markedly in sitting or standing subjects. Postural hypotension limits use of ganglionic blockers in ambulatory patients. 

Usual Predominance of Sympathetic or Parasympathetic Tone at Various Effector Sites, and Consequences of Autonomic Ganglionic Blockade... 

Treatment of cholinergic symptoms by autonomic ganglionic blockade would be undesirable in that the effect of such treatment is to abolish sympathetic as well as parasympathetic tone. Removal of sympathetic tone adds to the existing bradycardia and hypotension which form part of the syndrome of intoxication by cholinesterase inhibitors. 

E) Blockade of ganglionic transmission at sympathetic ganglia in the periphery... 

The answer is d. (Hardman, pp 192-193.) Nicotine is a depolarizing ganglionic blocking agent that initially stimulates and then blocks nicotinic muscular (NM) (skeletal muscle) and nicotinic neural (NN) (parasympathetic ganglia) cholinergic receptors. Blockade of the sympathetic division of the autonomic nervous system (ANS) results in arteriolar vasodilation, bradycardia, and hypotension. Blockade at the neuromuscu-... 

Effects of autonomic blockade on the response to phenylephrine (Phe) in a human subject. Left The cardiovascular effect of the selective K-agonist phenylephrine when given as an intravenous bolus to a subject with intact autonomic baroreflex function. Note that the increase in blood pressure (BP) is associated with a baroreflex-mediated compensatory decrease in heart rate (HR). Right The response in the same subject after autonomic reflexes were abolished by the ganglionic blocker trimethaphan. Note that resting blood pressure is decreased and heart rate is increased by trimethaphan because of sympathetic and parasympathetic withdrawal. In the absence of baroreflex buffering, approximately a tenfold lower dose of phenylephrine is required to produce a similar increase in blood pressure. Note also the lack of compensatory decrease in heart rate. 

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