There are many causes of laminitis, including dietary overloads, hormonal disruptions, toxic plants, severe intestinal disorders and bacterial infections. It has been estimated that 80% or more of laminitis cases fall under the category of hormonal/endocrine pathologies but until recently detailed research has focused on other causes.
Protein Structure of the Hormone Insulin
Research has shown that both toxic laminitis (black walnut) and hind gut carbohydrate overload (starch/fructan) are characterized by activation of tissue degrading matrix metalloproteinase enzymes, the MMPs, breakdown of the basement membrane and inflammation revealed by large numbers of invading neutrophil white blood cells.
However, studies over the past few years have shown that this does not happen with laminitis caused by high insulin, which may have a lot to do with why this type of laminitis does not respond particularly well to antiinflammatory drugs like phenylbutazone. The cascade of tissue destruction caused by inflammation does not occur in laminitis related to this hormonal disruption.
We do not yet understand the complete mechanism behind endocrinopathic laminitis but there are important clues. High levels of insulin lead to high levels of endothelin-1, an extremely potent vasoconstrictor which interferes with blood supply to the laminae. A large body of literature also links insulin resistance and oxidative stress, high levels of reactive oxygen species.
With acute endocrinopathic laminitis, the core of treatment is to reduce the simple sugar and starch content of the diet by feeding only low sugar/starch hay and supplements as needed to balance the minerals in the hay fed in a low sugar/starch carrier such as rinsed and soaked beet pulp, soybean hulls or Brewer’s/Distiller’s dried grains. Potent antioxidant supplements containing both plant based (e.g. Turmeric, Ginger, Grape Seed extract, Boswellia) and nutrient sources (N-acetyl-cysteine, vitamin C, lipoic acid, vitamin E) work just as well, if not better, in controlling pain in acute episodes compared to NSAID (nonsteroidal antiinflammatory) drugs and without the potent side effects.
Supporting blood flow to the hoof in the face of high endothelin-1 concentrations is also important. The herb Jiaogulan, Gynostemma pentaphylluma, is an extremely potent vasodilator. It is well accepted by horses, safe and effective in relieving pain in a high percentage of laminitic horses. It works by stimulating production of the vasodilator nitric oxide inside vessels. This is supported by supplementation with the amino acid L-arginine, the precursor for nitric oxide.
Endothelin-1 levels are even higher in horses with chronic laminitis pain, so nitric oxide support is indicated for these as well, in addition to meticulous attention to diet and an appropriate trim. There are also chronic cases where pain is contributed to by actual changes in the nerves and the spinal cord – neuropathic pain. Acetyl-L-carnitine, “ALCar”, is a naturally occurring metabolite of L-carnitine in the body and has shown clear benefit in different types of neuropathic pain in many species. It has also been effective in horses.
We have much more to learn about hormonal laminitis but have made decent inroads and the most important realization for moving forward is that this is different from other causes of laminitis. The solutions need to be different too.
Eleanor Kellon, VMD