An Investigation of the Assay of Heparin Based on Its Activity in Vivo^[*]

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.

^* This investigation was supported by a grant from the Saskatchewan Heart Foundation.

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