Studies on the slow contraction of smooth muscle produced by human plasma.

The slow contraction of smooth muscle produced by human plasma becomes less potent after storage of the plasma for six months at room temperature and after processing of the plasma with kaolin. These observations fall into line with the fact that 40% of the initial smooth-muscle-contracting activity of the plasma can be accounted for in the deposit which is formed during the six-months period of storage, and also with the fact that the recovery of G acid from human plasma treated with kaolin is about 50% of the yield which is obtained from the same plasma before kaolin treatment.