Do you have a horse with PPID? Do you really understand the disease, and what causes the symptoms that you see? This video by the makers of Prascend, Boehringer Ingelheim, explains clearly how excess hormones are produced in the pituitary gland in horses with PPID. Notes of the video are below (slightly edited).
The pituitary gland (master gland) lies at the base of the brain and is responsible for the production of an array of hormones, which circulate throughout the body and regulate the function of various organs. In a healthy horse the release of hormones from the pituitary gland is controlled by the hypothalamus. The hypothalamus generates releasing and inhibiting factors that act on the pituitary gland to stimulate/inhibit the secretion of specific pituitary hormones.
The equine pituitary gland is comprised of 3 lobes: pars distalis, pars intermedia (which is affected by PPID) and pars nervosa.
In the healthy horse, the production of hormones from the pars intermedia is inhibited by dopamine. Dopamine is released into the pars intermedia from neurons that originate in the hypothalamus. The dopamine binds to dopamine receptors on the surface of the cells of the pars intermedia, like a key in a lock. Once the receptor is occupied by dopamine, the dopamine receptor acts like a brake, inhibiting the production and release of hormones from the pars intermedia. In a healthy horse, ample dopamine is available to evoke a strong inhibitory action by the dopamine receptors to make sure just the right amount of alpha-MSH, beta-endorphin, ACTH and CLIP is produced by the pars intermedia.
PPID originates from the degeneration of the dopamine producing neurons in the hypothalamus. The lack of sufficient dopamine in the pars intermedia leads to increased hormone production. The pars intermedia hormone concentrations in a horse with PPID may be more than 100 times greater than in a healthy horse. Absence of dopamine allows the cells of the pars intermedia to divide and enlarge, causing the pituitary gland to increase to 2 to 6 times normal size. Expansion of the pars intermedia causes the other pituitary lobes to become compressed.
The lack of dopamine in horses with PPID can be managed by using Prascend. Prascend is a dopamine agonist – it acts to replace the dopamine missing from the pars intermedia. By binding to dopamine receptors, it decreases the secretion of pars intermedia hormones which leads to improvement in symptoms, e.g. improved hair coat, muscle mass and attitude, less risk of developing laminitis and secondary infections. Prascend hasn’t been evaluated in breeding, pregnant and lactating horses – it is a dopamine agonist and therefore may interfere with reproductive hormones, and is likely to prevent/lessen milk production (due to effects on prolactin).