Theories and causes

ADAMTS-4

One enzyme of interest is the cartilage destroying enzyme ADAMTS-4. In the lamellae a protein is present that is degraded by this enzyme. Too much of this enzyme could lead to weakening of the lamellae and therefore weakening of the lamellar connection. The focus on MMP-2 and MMP-9 has now shifted to ADAMTS-4.

The basement membrane

Searching for the cause of laminitis in a different direction does not change the fact that the basement membrane cells – the hemidesmosomes – and the secondary epidermal lamellae deteriorate. They change shape and start to slide over one another. Also the amount of hemidesmosomes decreases. The lamellar connection gradually disintegrates.

This deterioration has been observed by researchers within 12 hours after the onset of laminitis. This is even before any clinical signs can be observed.

Degradation of the basement membrane does not only take place in the hoof. Also, the skin and chestnuts suffer from it. However consequences are far less disastrous because these tissues are less structural compared to hoof tissues.

Hoof vasculature

The capillaries that provide blood to this area of the hoof get damaged as well. Blood is instantly transferred via the shunts from the blood supplying arteries to the blood draining veins. The foot itself is short-circuited by this.

The damaged capillaries and short-circuiting of the hoof are the reasons veterinarians often prescribe vasodilator and anticoagulant drugs. Unfortunately, the latter are often erroneously called blood-thinners. By inhibiting clotting of the blood a superficial wound will indeed bleed longer. This gave rise to the idea that these drugs made the blood thinner. However this is not the case. In addition, the thickness of the blood is not the problem, nor the width of the capillaries. In any case, these symptom controlling drugs hardly reach the hoof at all because of the occurrence of shunting.

Conventional treatment

Based on this theory, treatment of laminitis focuses on lowering enzyme activity. According to researchers that subscribe to this theory, during the developmental phase vasodilation takes place in the hoof, causing the supply of TIMPs and MMP triggers to be higher than normal. The reduction of blood supply would therefore be helpful.

This is in stark contrast to the circulation theory (and the trauma theory) in which blood supply is stimulated. Blood circulation can be decreased by cold therapy. Decreasing the blood pressure also slightly reduces blood flow.

The administration of enzyme inhibitors to reduce the MMPs (such as MMP-2 and ADAMTS-4) could be effective as well, however it is important to take potential harmful side effects of these drugs into account.

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