THE SEAT OF THE EMETIC ACTION OF PILOCARPINE

¹ From the Department of Pharmacology of Cornell University Medical College, New York City

The present investigation is concerned with the emetic action of moderate intravenous doses (2 mgm.) of pilocarpine in the cat and dog.

A. Moderate doses of pilocarpine induce vomiting in the cat and dog through their peripheral action on the parasympathetic type of afferent nerve endings which transmit impulses to the center mainly through the sympathetic trunk.

B. Atropine abolishes the emetic action of pilocarpine by its direct depressant action on the same nerve endings.

These statements are supported by the following evidence:

A. 1. The emetic action of pilocarpine in the dog is inhibited completely by cutting off all afferent nerve paths from the heart to the center (section of the cord at the level of the second thoracic vertebra and the vagi at the level of the sixth cervical vertebra; section of the cord at the level of the sixth thoracic vertebra does not inhibit it).

2. The emetic action of pilocarpine in the cat is usually inhibited by extirpation of the stellate ganglia.

3. The foregoing direct evidence is supported by the fact that the direct application of pilocarpine to the center does not induce vomiting.

B. 1. "Doses of atropine (5 mgm. in 1 per cent solution) applied to the gastric or intestinal mucosa prevent copper sulphate vomiting, indicating a depression of autonomic afferent endings" (Koppanyi) (11).

2. The local application of atropine abolishes the action of pilocarpine previously induced in the eye and in the intestine, and in the skin of the frog, and it abolishes nearly all other peripheral effects of pilocarpine.

3. The intravenous injection of 0.01 mgm. of atropine abolishes the emetic action of a minimal dose of pilocarpine, but 500 times that dose of atropine has no perceptible effect on the emetic action of minimal doses of apomorphine and morphine on the vomiting center (Eggleston). The intramuscular injection of 5 mgm. of atropine sulphate (500 times the minimum effective intravenous dose against pilocarpine) has no influence on the emetic action of a minimal dose of nicotine salicylate (0.01 mgm.) applied directly to the vomiting center in the dog.

4. The direct application of a relatively large dose (0.02 mgm.) of atropine to the vomiting center has no influence on the emetic action of nearly minimal doses of morphine or apomorphine applied directly to the center (Hatcher and Weiss).