Acetylcholine and the sympathetic innervation of the spleen.

This paper is concerned with the role of acetylcholine-like substances in the sympathetic innervation of the spleen. The presence of cholinergic fibres in the sympathetic nerve supply to the cat's spleen was deduced by Burn & Rand (1960c) from observations on the response of the spleen of reserpine-treated cats to splenic nerve stimulation. Stimulation of the splenic nerve in a normal cat releases noradrenaline (Peart, 1949) and causes contraction of the spleen. But when the spleen is depleted of noradrenaline by reserpine (Burn & Rand, 1959 a), splenic nerve stimulation produces either a smaller contraction than usual or a relaxation which is enhanced by eserine and abolished by atropine. The innervation of the cat's spleen has been studied by Utterback (1944), who concluded that there was no parasympathetic innervation and that there were no ganglion cells in the spleen. Sympathetic denervation leads to a decrease in the noradrenaline content of the spleen (von Euler & Purkhold, 1951; Burn & Rand, 1959a), and von Euler (1956) concluded that the loss of noradrenaline on denervation could be explained if it were normally contained in the nerves. However, in another sympathetically innervated structure, the vessels of the rabbit's ear, denervation has been shown to cause a fall in acetylcholine content (Armin, Grant, Thompson & Tickner, 1953). It is well known that the spleen contains acetylcholine. This was first observed by Dale & Dudley (1929), although as yet no explanation has been given for its presence. In order to investigate the possibility that the acetylcholine might be associated with the splenic nerves, we have studied the effect of sympathetic denervation on the acetylcholine content of the cat's spleen. Acetylcholine has been detected in the venous effluents after the stimulation of the sympathetic nerves to a number of structures: the sweat glands (Dale & Feldberg, 1934), the blood vessels of the dog's hind legs