In the fall, measuring a horses adrenocorticotropic hormone (ACTH) levels is often used as a diagnostic tool for pituitary pars intermedia dysfunction (PPID, also known as equine Cushing’s disease). It peaks between mid-August to mid-October as part of the metabolic preparation for winter and results in levels anywhere up to about three times those found at other times of the year. It used to be thought that this made early fall a poor time of year to use ACTH levels as a diagnostic tool. However, in recent years, research has shown that horses with PPID have a seasonal rise that is even higher than unaffected horses. Contrary to previous belief this might in fact make fall a good time of year to test due to the potential for a more profound response to the seasonal ACTH rise in horses with PPID.
The pituitary tumors associated with PPID influences the adrenal glands to release cortisol, a stress-related hormone. Cortisol plays an important role in the metabolism of carbohydrates, proteins, and fats and helps to balance the effects of insulin in the breakdown of sugar for energy. It is a vitally important hormone; however, when elevated for extended periods, as in the case of high circulating ACTH, high cortisol levels could have some negative consequences. These include inducing a degree of insulin resistance (IR), muscle wasting, a pot-belly appearance, immune deficiency, and an increased susceptibility to infections.
You horse’s elevated insulin level might be the result of the effects of the elevated ACTH on cortisol levels due to PPID. Of course some horses have high levels of circulating insulin indicative of IR without having PPID. But in horses with PPID, especially those not considered to be at risk of IR, IR is commonly the result of the PPID. read more…