A STUDY OF THE SUBSTANCES IN BLOOD SERUM AND PLATELETS WHICH STIMULATE SMOOTH MUSCLE

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Abstract
Serum and lysed platelets stimulate the smooth muscle of the rat duodenum, cat nictitating membrane (n.m.) and the vessels of the rabbit ear, whereas plasma and hemolysed red cells have at most a slight effect on these indicators. Lysed lymphocytes are devoid of activity on the n.m. or intestine; lymph stimulates the n.m., and rabbit ear vessels and inhibits the intestine. A pharmacologically active fraction (SMC) was prepared from the buffy coat of human blood by precipitating the proteins with acetone, extracting the filtrate with ether, and using the fraction of the dried ether insoluble residue which is soluble in methanol. SMC stimulates the smooth muscle of the intestine, uterus, carotid artery, n.m., pupillary sphincter, and vessels of the cat tail, but fails to affect the vessels of the rabbit ear. The action of cat serum on the n.m. is abolished by incubation with cat lung or kidney, or with rat lung or skeletal muscle, but not with cat spleen or skeletal muscle. The substance in SMC which stimulates the n.m. is destroyed by incubation with cat lung or rat lung, kidney, liver, intestine or skeletal muscle and by prolonged boiling in 1 N HC1 but not by incubation with rat spleen nor by boiling in 1 N NaOH. The activity of SMC or serum on the intestine and cat tail vessels is affected by incubation with tissues or by treatment with acid and alkali in the same manner as is its activity on the n.m. Expts. indicate that a single substance is responsible for the action of both SMC and serum on the intestine, n.m. and cat tail vessels. The evidence for the existence of other smooth muscle stimulating substances in serum and platelets is discussed.

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