Further studies of the interaction between ristocetin and fibrinogen.

Fibrinogen (FG) precipitation by ristocetin is enhanced by lowering the temperature to 4 degrees C. The precipitate has similar properties to an acquired cryofibrinogen being resolubilised on rewarming to 37 degrees C, and the process of precipitation and resolubilsation can be repeated indefinitely by lowering and raising the temperature. Other plasma proteins are also precipitated by ristocetin, but to a lesser degree than FG. This property appears to have no relation to ristocetin's ability to aggregate platelets in the presence of von Willebrand's factor, since platelet aggregation by ristocetin is inhibited by lowering the temperature.