Factors affecting the quantitative response of human eccrine sweat glands to intradermal injections of acetylcholine and methacholine.

1. Using a ventilated capsule in conjunction with an infra-red water vapour analyser, and an indwelling intradermal needle, quantitative studies were made relating the magnitude of the sweat responses to the doses of acetylcholine or methacholine.2. Acetylcholine dose-response curves were constructed, and from these curves the threshold dose was defined. The threshold was similar in all subjects (10(-3) +/- S.E. 10(-4) mug/0.1 ml.).3. Factors affecting the acetylcholine dose-response curves were studied. Optimum conditions for stimulation in all subjects occurred using a capsule of 0.63 cm diameter, injection volume of 0.1 ml. and a solution temperature of 37 degrees C. When the skin temperature was 36 degrees C the maximal acetylcholine response was then the same as the maximal thermal response.4. No change in the acetylcholine dose-response curves occurred with repeated determinations at the same site on the same occasion.5. The dose-response relationship for methacholine was similar to that for acetylcholine. The methacholine response was, however, more prolonged and so the volumes secreted were greater.