Studies on the differences in activity of lung and brain thromboplastin.

Recent reports have suggested that thromboplastin (Tpl) prepared from lung may reflect more accurately than does brain Tpl the changes produced in the prothrombin complex by coumarin derivatives (1, 2). As evidence for this, it has been observed that as factor VII concentration decreases in the plasma of Dicumarol '-treated patients, the prothrombin time obtained with lung Tpl becomes disproportionately longer than that obtained with brain Tpl (1). The inference from this observation has been that brain Tpl contains a factor VII-like activity, not possessed by lung Tpl. This activity would mask a lowered plasma concentration of factor VII and would result in spuriously short prothrombin times. Verstraete, Clark and Wright (1, 2) concluded that brain thromboplastins possess, although to a lesser degree, the disadvantage previously observed for Russell's viper venom (3, 4). The latter, by virtue of its intrinsic convertin-like activity, is insensitive to changes in factor VII concentration and is, therefore, no longer used in following anticoagulated patients. Other observations, however, suggest that brain Tpl does not contain more factor VII activity than does lung and may, in fact, contain less. Mann and Hurn (5) have noted that contamination of the Tpl with small quantities of blood may result in marked enhancement of activity when tested on the plasma of patients receiving coumarin derivatives. If the factor VII-like activity of tissue Tpl was due to contamination by blood and not to intrinsic properties of Tpl itself, one would expect brain Tpl to show less such activity than lung Tpl, inasmuch as lung preparations are more heavily contaminated by blood during their preparation. In addition, Verstraete and associates (1) found that when Tpl solutions were adsorbed with BaSO4, lung Tpl showed a pronounced decrease