The periodicity of microfilariae VII. The effect of parasympathetic stimulants upon the distribution of microfilariae

Abstract
1) Acetylcholine (intravenous) and carbachol (intramuscular) cause a rise in the microfilaria count of Dirofilaria immitis and of D. repens in dogs., i.e., they cause liberation of microfilariae from the lungs. This effect is partially antagonized by the previous administration of atropine. Acetylcholine has no obvious effect upon the motility of microfilariae of D. repens in vitro, and the effect upon the microfilariae in the dog must be due to some modification of the relationship between the microfilariae and the pulmonary capillaries. 2) Rise in the microfilaria count is caused also with Monnigofilaria setariosa of the mongoose, with Dipetalonema witei of the jird (by acetylcholine but not by carbachol) and with Litomosoides carinii of the cotton-rat (by carbachol but not by acetylcholine). No effect (rise or fall) was produced by acetylcholine or pilocarpine with the microfilariae of Wuchereria bancrofti of man, or of Brugia pahangi in the cat. 3) Atropine, which would paralyse parasympathetic nerve-endings, did not antagonize the actions of oxygen or of muscular exercise in causing a fall in the microfilaria count of W. bancrofti, i.e., reaccumulation of microfilariae in the lungs. 4) Apparently microfilarial periodicity in man does not depend upon the parasympathetic nervous system.