Abstract
1. The algesic effect of several substances following intraarterial injection into the rabbit ear was measured: by recording the action potentials of the auricular nerve in the isolated ear (method A) and by recording the reflex fall in systemic blood pressure elicited by intraarterial injection into the isolated perfused ear which was still connected to the body by the nerve (method B). 2. The order of activity of the algesic substances was: bradykinin, substance P>ACh>ATP, histamine, serotonin, KCl. A good correlation of the actions of all substances tested was found in both preparations. Physalaemin, eledoisin, adenosine, adrenaline, angiotensin, vasopressin, oxytocin and prostaglandin E1 were found to be inactive. 3. Infusion of prostaglandin E1 into the ear, however, enhanced the effect of all substances. 4. The vasoconstriction in the ear observed with most of the substances was not correlated with their activity in eliciting afferent impulses.
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