Sympathetic and Parasympathetic Responses after Intradermal and Intracorneal Injections

Abstract

In a recent series of papers Luithlen and Molitor 1 have reported that following an intradermal or intracorneal injection of 0.1 cc. of 0.9 per cent NaCl solution in a cat, the response of the vagus either to an electrical stimulus or to a parasympathetic-stimulating drug (cholazyl) is greatly increased. Both vagus trunks were cut, the electrical stimulus being applied peripherally; the drug was injected intravenously. They report that they were able to get a constant series of control responses to electrical or drug stimulation before the intradermal or intracorneal injection. They find that the enhancing effect is not obtained when the intradermal injection is made into a denervated area and conclude that it is due to a reflex heightening of vagus sensitivity, the afferent path being afferent fibers stimulated by the injected solution. It is difficult to see how peripheral manifestations of reflexly increased vagus tone can be elicited when both vagus trunks are cut. These workers also report an increased response to adrenalin after intradermal and more especially after intracorneal injection, attributing this to a reflexly increased sympathetic sensitivity. The increase in sympathetic response was less nearly constant than the increase in the parasympathetic response.

Since these results were so surprising it seemed worth while to repeat these experiments. The precautions prescribed by Luithlen and Molitor as essential to success were carefully observed, namely, proper preparation of the site of intradermal injection, maintenance of body temperature, anesthesia, etc. Shielded electrodes were used for nerve stimulation, the source of current being a chloride accumulator. The drug injections were made into a femoral vein, the injection time being 10 seconds. Arecoline was the parasympathetic drug employed, adrenalin the sympathetic. Adrenalin dilutions were made from a 1–1000 Parke-Davis preparation, no dilution more than 12 minutes old being used.