The rabbit is a well established model for studying the disseminated intravascular
coagulation (DIC) associated with endotoxic syndromes. In order to establish the role
of antithrombin III (AT III) in the modulation of DIC in the rabbit, characterization
of rabbit AT III was undertaken. Rabbit antithrombin III, isolated according to modifications
of the method of Thaler and Schmer, has a molecular weight comparable to that of human
AT III (62,000 daltons) as measured by mobility on SDS-PAGE gels. Mixtures of rabbit
and human AT III co-migrate as a single band on 7.5% SDS-PAGE gels. Rabbit AT III
possesses both progressive and heparin activated (immediate) antithrombin activity
in assays using human thrombin. Antisera raised against rabbit AT III demonstrates
no cross reactivity with human AT III suggesting that despite physiologic and molecular
weight similarities, antigenic differences are present. Incubation of rabbit antithrombin
III with specific antisera, either prior to or after addition of heparin, did not
alter the ability of antithrombin III to inhibit thrombin in either the immediate
or progressive assays indicating that the antigenic determinants are not found in
either the heparin binding or active thrombin binding sites. Crossed immunoelectrophoresis
(IEP) demonstrates that antisera to rabbit AT III reacts with both free rabbit antithrombin
III and AT III-thrombin complexes and can therefore be used in immunologic assays
to quantitate total rabbit AT III (bound and free) and in crossed IEP to demonstrate
the mobility of both free and complexed AT III.
