The pituitary is a small gland located near the base of the horse's brain. It regulates almost all of the body's endocrine (hormonal) systems. It is often called the "master gland."
The hypothalamus, located near the pituitary, works in conjunction with the pituitary gland to regulate the body's systems. Hormones produced by the pituitary and hypothalamus influence the adrenal glands to produce or not produce cortisol.
In pituitary pars intermedia dysfunction (PPID), a common disease of older horses, the pituitary gland enlarges and forms a benign tumor. This tumor secretes excessive amounts of multiple proteins, which leads to significant increases in the stress hormone cortisol.
This elevation in cortisol and other proteins result in excessive hair growth, excessive drinking and urination and laminitis. In humans and dogs, high levels of cortisol can also lead to inappropriate blood clotting.
A student at Tufts University evaluated horses with PPID to determine whether they also exhibit inappropriate blood clotting.
To test for clotting, the student drew blood from horses with PPID and without PPID and examined the process of clot formation to the point when the clot is broken down.
The testing method in this study examined both blood cells and plasma (the liquid portion of blood) and looked at the plasma proteins that are considered to be accurate indicators of coagulation.
The results of this study indicate that, in contrast to dogs and humans,horses with PPID are not at higher risk for the formation of blood clots compared to normal horses.