LOCUS OF EMETIC ACTION OF EPINEPHRINE AND DOPA IN DOGS

¹ Department of Physiology, National Taiwan University College of Medicine, Taipei, Taiwan

Intravenous injection of epinephrine and dopa induced vomiting in dogs after an average latency of 70 seconds and 117 seconds, respectively. The ED50 of epinephrine HCl and dopa in provoking emesis in dogs is 0.052 mg/kg and 0.79 mg/kg, respectively. Epinephrine is 15.0 times more potent than dopa in inducing emesis.

Epinephrine-induced emesis was only inconsistently blocked by trigger zone ablation. There was no correlation between the elevation of emetic threshold to epinephrine and the elevation of the apomorphine threshold or the completeness of trigger zone ablation. On the other hand, the same operation renders dogs completely refractory to dopa-induced emesis. Gut denervation did not alter its threshold. These results suggest that dopa, like apomorphine, provokes emesis only via the trigger mechanism.

Perphenazine was highly effective in preventing emesis induced by dopa, but not as effective in preventing that caused by epinephrine. On the other hand, the antiemetic effects of glycine against dopa and epinephrine do not differ. Atropine exerted no antiemetic effect on epinephrine-induced emesis.