PHYSIOLOGY AND BIOCHEMISTRY OF SHOCK 417 



postganglionic nerve endings of the parasympathetic nervous system 

 producing dilation of blood vessels, increased tone of bronchioles and 

 gut, slowing of the heart, and increased glandular secretion; the use of 

 the term muscarinic action is related to these actions of acetylcholine. 

 Like the alkaloid nicotine, acetylcholine acts on all the autonomic 

 ganglia, both sympathetic and parasympathetic and on the skeletal 

 myoneural junction. It stimulates these when used in small doses and 

 paralyzes them when large doses are used. These effects of acetylcho- 

 line on autonomic ganglia and on voluntary myoneural junctions is 

 called nicotinic. 



c. Antagonists to Acetylcholine. Ergotamine, nicotine, curare, and 

 atropine are antagonists of acetylcholine. Atrofine blocks all the mus- 

 carinic action of acetylcholine whether they are excitatory as in the 

 intestine, or inhibitory as in the heart. Nicotine and curare block only 

 the nicotinic action of acetylcholine, nicotine acting especially on the 

 ganglia and curare on striated muscle. In a system where both striated 

 and smooth muscles are present (i.e., intestine of the fench, a primitive 

 fish, see Goodman and Gilman, 1941), the application of both atro- 

 pine and curare obviates the contraction of the organ; atropine 

 specifically blocks the action of acetylcholine on the smooth muscle, 

 and curare specifically blocks that on the striated muscle of the system. 



Curare, although having the same points of attack as acetylcholine, 

 has only a paralyzing effect. It acts at the neuromuscular junction, 

 that is, it prevents the end-plate from responding normally. If curare 

 is eliminated— excretion, washing, etc.— the neuromuscular transmis- 

 sion is re-established. 



Pilocar'pine is believed to act highly selectively on structures supplied 

 by postganglionic cholinergic nerves. In this respect, pilocarpine shows 

 the muscarinic and not the nicotinic effects of acetylcholine. Muscular 

 and glandular responses occur to muscarine and pilocarpine after com- 

 plete nerve degeneration. Similarly, evidence from frog single fibers 

 suggests that even in denervated muscles, the end-plate region remains 

 especially sensitive to depolarization and stimulation by acetylcholine 

 (Kuffler, 1946). 



d. The Role of Acetylcholine on the Effector Organs. Acetyl- 

 choline by its muscarinic action and cholinergic impulses which release 

 acetylcholine have been known to produce constriction of bronchial 

 muscle, and secretion of bronchial glands; increase of the secretion and 



