The leech’s power is chemical. Its saliva is a pharmacy of bioactive molecules, and hirudin — a direct thrombin inhibitor — is the most famous of them.
Hirudin binds thrombin with extraordinary specificity, blocking the conversion of fibrinogen to fibrin and thereby preventing clot formation at the bite. This is what produces the prolonged, controlled bleeding that decongests tissue after the animal has detached.
More than one molecule
Hirudin rarely acts alone. Leech saliva also contains compounds that inhibit platelet aggregation, dilate local vessels and dampen inflammation — a coordinated mix that sustains microcirculation at the wound while the animal feeds and afterwards.
- Hirudin — direct thrombin inhibition
- Platelet-aggregation inhibitors
- Vasodilatory and anti-inflammatory factors
Why species and grade matter
The salivary profile is a property of a healthy, well-conditioned animal. Wild-harvested or poorly held leeches are an unknown quantity; medical-grade, fasted stock is what makes the pharmacology predictable.