Mechanism of the emetic action of nicotine and lobeline

The emetic action of nicotine and lobeline was studied in cats and dogs. The minimal uniformly effective emetic doses were found to be 1.5 mg/kg I.M. nicotine bitartrate and 0.5 mg/kg I.M. lobeline sulfate. In terms of the alkaloid base, the dose-response relationship coincided, for practical purposes, at all dose levels studies. Sixty-six cats and ten dogs were used to establish the locus of the emetic action of the alkaloids. It was found, in cats, the agents stimulated two different sites of action, namely, a peripheral locus ( or loci) as well as the CT-zone. Therefore, in order to eliminate vomiting response to nicotine and lobeline in cats, it was necessary to combine the following procedures: spinal visceral deafferentation, vagotomy, and CT-zone ablation. The combination of these lesions was accomplished either by peripheral nerve sections in combination with CT-zone ablation or by a broad medullary lesion with destroyed both the CT-zone and incoming visceral afferents. The dogs, CT-zone ablation alone sufficed to protect animals against the emetic effect of nicotine and lobeline. The implication of these results in discussed in light of investigations of species variations previously reported in this field. Anti-emetic drug studies were also included in the present investigation. Tetraethylammonium (TEA) was effective in preventing emesis in response to nicotine in both cats and dogs, but it was effective only against lobeline in cats. Hexamethonium (C6) protected both species against uniformly effective emetic doses of nicotine and lobeline. Neither atropine nor chlorpromazine was found significantly to protect animal of either species against the emetic action of nicotine and lobeline.