, Volume 9, Issue 3, pp 125-131

Prolonged bleeding from the bite of the Asian medicinal leechHirudo nipponia

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Abstract

Selected antihaemostatic parameters associated with the bite of the Asian medicinal leechHirudo nipponia were investigated in human volunteers. This study confirms earlier work onHirudo medicinalis, in that the wound from a leech bite bleeds for hours even though blood coagulates normally after about 15 min. The whole blood clotting time forH. nipponia after 1 min was 12.88±3.15 min, comparable to that forH. medicinalis, but in both cases clotting time returned to control levels after about 15 min. However, the duration of bleeding from the bite ofH. nipponia (mean=210 min) was consistently shorter thanH. medicinalis, even when adjusted for size differences (mean=490 min). Similarly, the blood flow rate fromH. nipponia (mean-39 μl/min) is markedly slower thanH. medicinalis (mean =200 μl/min). The total blood lost from the host, therefore, was approximately ten times more withH. medicinalis thanH. nipponia. Collagen-induced platelet aggregation was significantly impaired in blood from theH. nipponia bite wound in 25 min. This may indicate that the prolongation of bleeding is caused by inhibition of platelet aggregation rather than by thrombin inhibition alone.

In both species, the saliva of the leech contains a potent antithrombin whose inhibitory activity returns to normal levels approximately 15 min after cessation of feeding. The internal amino acid sequence of the thrombin inhibitor secreted byH. nipponia into the saliva is unexpectedly different (55%) from that of hirudin secreted byH. medicinalis. This difference in sequence is reflected in the lack of neutralisation by the polyclonal antibody to hurudin fromH. medicinalis. Blockage of the N-terminal in antithrombin fromH. nipponia appears to be a further real difference compared to hirudin fromH. medicinalis.

The biological significance, if any, of these differences between species in bleeding time and antithrombin structure remains an open, but intriguing, question.