Summary
The potency of different heparin preparations was investigated in vivo, by measuring
the Lee and White clotting time, lipolytic activity and partial thromboplastin time
of blood samples drawn at intervals after the intravenous injection of heparin into
the anesthetized dog. The blood clotting time in log minutes, the thromboplastin time
in log seconds, and the plasma lipolytic activity measured as the decrease in optical
density of a synthetic cocuont oil emulsion per unit of time after incubation with
postheparin plasma, were plotted against time after injection. A linear relation was
obtained between the dose of heparin and the response measured as the area under the
curve.
The in vivo responses for 6 heparin preparations at 3 dose levels were compared with
those for a reference heparin. The potency of each relative to the reference was estimated
as the ratio of equally effective doses. The results obtained were compared with assay
values reported for in vitro tests - U.S.P. , Howell, colorimetric (Lovibond, Beckman
DK-2 spectrophotometer and microelectrophoresis on agarose) . There was no consistent
case of one assay methodgiving results greatly different from the others and no assay
method consistently described the activity of the heparin preparation in another test
system, in vitro or in vivo.
