Nature's Lubricant: Sodium Hyaluronate

Sodium hyaluronate is often called "hyaluronic acid," although this is a misnomer. At normal physiologcal pH values, the acid can occur only as its sodium salt, i.e., as sodium hyaluronate.

Sodium hyaluronate, the active substance in HYLARTIN^® V Injection (sodium hyaluronate), is found in all living organisms and has numerous functions in the body. It contributes to elasticity and pliability in connective tissue and skin. High levels of sodium hyaluronate are also found in the vitreous body of the eye and in the umbilical cord. In joints, sodium hyaluronate combines with proteoglycans to form giant molecular complexes that provide the elastic, shock-absorbing properties of cartilage. High-molecular-weight sodium hyaluronate is necessary for the synovial fluid to accomplish its most important duties.

• Shock absorption - Dissipates the energy from hoof impact during running, stopping, turning and other strenuous activity, preventing damage to bone and tissues



• Lubrication - Reduces friction between the soft tissues of the joint cavity



• Blocking - Locks out leukocytes with their cartilage-degrading enzymes from the joint cavity



• Feeding - The network formed by the long molecular chains acts as a sponge to absorb and release liquid during joint action. This process allows glucose and other nutrients to move from the blood vessels of the joint capsule through the synovial fluid into the cartilage cells

Most of the frictional resistance in a joint is caused by soft tissues rubbing against each other or against the surface of cartilage. High-molecular-weight sodium hyaluronate is critical because it lubricates these tissues. When a joint is inflamed, the synovial membrane and joint capsule swell, leading to increased friction. At the same time, the sodium hyaluronate is degraded to a low molecular weight and grade, reducing the synovial fluid's role as a lubricant. Increased friction contributes greatly to the pain and lack of mobility associated with inflamed joints.

Chemically, sodium hyaluronate is a polysaccharide chain with a naturally high molecular weight. When dissolved, the long chain gives a solution certain characteristics that can actually be seen by the naked eye.

A solution of sodium hyaluronate (1-percent solution, molecular weight 3 million daltons) is pressed through a cannula onto a glass rod. Because of its high viscosity and elasticity, the solution remains on the rod, and the string of solution expands as it leaves the cannula.

Synovial fluid from horses normally contains 1.3 mg sodium hyaluronate per mL. Long hyaluronate molecules intertwine and wind in the synovial fluid to form a filter of random coils of entangled molecules. This filter keeps out leukocytes and their damaging enzymes. It also binds water molecules to prevent turbulence in the synovial fluid. On the other hand, the filter allows glucose, electrolytes and other low-molecular-weight substances, all important to normal joint function, to move through the barrier easily because of their small size.

Natural sodium hyaluronate serves as a barrier to protect tissues within the joint cavity. Injecting low-molecular-weight sodium hyaluronate as therapy has little or no effect. Here's why:

• The short molecular chains of low-molecular-weight sodium hyaluronate cannot form entangled molecules with the same efficiency as high-molecular-weight sodium hyaluronate, such as HYLARTIN V



• Low-molecular-weight sodium hyaluronate cannot provide long-lasting lubrication, because it is incapable of stimulating the synovial membrane to synthesize hyaluronate normally



• Low-molecular-weight sodium hyaluronate allows leukocytes and various enzymes to flow into the synovial cavity and synovial fluid, where they begin to deteriorate cartilage when they reach joint surfaces

As with all intra-articular injections, occasional mild side effects may include heat, transient edema and pain around the injection site.

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