Abstract
A number of authors 1 2 3 4 5 6 have described the vasopressor effect of large doses of normally vasodilator choline derivatives in atropinized animals, including the “parasympathetic substance’ acetylcholine. The findings of Hunt 7 and Broun and Beaune 8 on these subjects will be discussed in a detailed paper.
All drugs used in these experiments were given intravenously and the doses expressed in milligrams per kg. In 6 cats, 4 rabbits and 10 dogs anesthetized with barbiturates, it was found that acetylcholine in doses of 0.05 to 0.1 mg. did not produce vasopressor effects following the administration of 2 to 5 mg. of atropine sulphate. If the administration of acetylcholine was preceded by 0.3 to 2 mg. of physostigmine salicylate in atropinized animals, acetylcholine produced sharp, epinephrine-like rises in the blood pressure of 50 to 100 mm. of Hg. in cats and dogs, and lesser rises in rabbits. These pressor effects with acetylcholine may be elicited many times over a period of 6 hours in atropinized animals following a single dose of 0.5 to 1.0 mg. of physostigmine salicylate.
This action of physostigmine on the responses of small doses of acetylcholine in atropinized animals may be ascribed to a ganglionic action of this drug in facilitating the cholinergic effect of acetylcholine through the sympathetic synapses.
The injection of 3 mg. of cocaine hydrochloride enhanced the vasopressor effects of acetylcholine under the above conditions, but could not elicit vasopressor responses from small doses of acetylcholine in a physostigmine-like manner.
The injections of 0.1 to 1.0 mg. of pilocarpine produced vasodilator effects which were completely antagonized by atropine. Following atropinization, pilocarpine even in doses of 10 to 50 mg. produced no typical effects in the presence of physostigmine.
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