Carotid body, nicotine effects

Chapter 28). Stimulation of nicotinic receptors in adrenergic nerve terminals leads to the release of norepinephrine and activation of nicotinic chemoreceptors in the aortic arch and carotid bodies causes nausea and vomiting. Nicotinic receptors in the central nervous system mediate a complex range of excitatory and inhibitory effects. 

Low doses of nicotine stimulate respiration through activation of chemoreceptors in the aortic arch and carotid bodies, while high doses directly stimulate the respiratory centers. In toxic doses, nicotine depresses respiration by inhibiting the respiratory centers in the brainstem and by a complex action at the receptors at the neuromuscular junction of the respiratory muscles. At these neuromuscular receptors, nicotine appears to occupy the receptors, and the end plate is depolarized. After this, the muscle accommodates and relaxes. These central and peripheral effects paralyze the respiratory muscles. 

Nicotine, like ACh, will stimulate a number of sensory receptors. These include mechanore-ceptors that respond to stretch or pressure of the skin, mesentery, tongue, lung, and stomach chemoreceptors of the carotid body thermal receptors of the skin and tongue and pain receptors. Prior administration of hexamethonium prevents stirmilation of the sensory receptors by nicotine but has little, if any, effect on the activation of sensory receptors by physiological stimuli. 

A number of choline derivatives also possess nicotinic and muscarinic effects. The nicotinic action induces excitation of aortic and carotid body chemoceptors and thus reflex stimulation of the respiratory center. 

Doses from/with smoking. Nicotine causes release of catecholamines in the CNS, also serotonin, and antidiuretic hormone, corticotrophin and growth hormone. The effects of nicotine on viscera are probably largely reflex, from stimulation of sensory receptors (chemoreceptors) in the carotid and aortic bodies, pulmonary circulation and left ventricle. Some of the results are mutually antagonistic. 

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