As most people are aware, laminitis is not a disease a horse suffers, but rather a symptom of an underlying endocrine (hormone) imbalance that must be addressed to combat the issue. The two most common endocrine diseases that cause laminitis in the horse are Pituitary Pars Intermedia Dysfunction (PPID) and Equine Metabolic Syndrome (EMS).
PPID is a condition that affects a specific part of the pituitary gland and results in the excess production of a chemical (POMC) that is further broken down into the hormones ACTH, alpha=MSH and B-END. This was discussed in more detail in a previous edition of (Equestrian Life, Issue 50 September/October 2019) so I will not go into PPID in too much depth here. One of these hormones produced in high amounts is ACTH and this triggers an increase in the production of cortisol. Cortisol is a stress hormone designed to increase sugar levels in the blood so that energy is readily available to the horse in the event of a flight or fight scenario.
EMS is a disorder that primarily occurs when the body fails to regulate insulin levels appropriately (insulin dysregulation), and it is linked to a failure of muscle, liver, and adipose cells responding to insulin (insulin resistance). This dysregulation causes the pancreas to keep releasing more and more insulin, leading to hyperinsulinemia (high levels of insulin in the blood).
In normal horses, insulin controls the level of glucose in the blood; it is released when glucose is high and effectively pushes glucose into cells or into pathways that turn glucose into complex sugars or fats that can be stored. When the glucose levels drop below a base level, insulin production and release is turned off, allowing complex sugar compounds and fats to be broken down into glucose that can be immediately utilised as an energy source.
Chronically high levels of glucose in the blood, as can occur with PPID sufferers, initially cause high sustained insulin levels in the blood that eventually become uncontrollable, leading to insulin dysregulation. Once the pony or horse has insulin dysregulation, the sugar levels cannot be controlled effectively with normal levels of insulin, leading to hyperinsulinemia and insulin resistance. The pancreas will continue to produce and release insulin to drive the glucose level down, maintaining this hyperinsulinemia that we now know is the cause of laminitis.