Regulation of body potassium is very complicated and is strictly controlled by hormones throughout the body produced by the kidneys, adrenal gland, thyroid and pancreas. Because normal horses commonly consume an excess of potassium in their diets, the kidneys must excrete excess potassium in urine. Initially, it could not be determined whether this disease was caused by a disorder in potassium regulation or by a disorder of muscle function. Studies of kidney, adrenal gland and thyroid function in horses with HYPP were normal. Investigations of muscle function in these horses, however, revealed a different story.
Electromyography measures the electrical activity present in selected muscles.
In affected horses, the muscles displayed a wide variety of abnormalities, specifically spontaneous activity from muscles under no stimulation. Even when the horses appeared normal, in between attacks, the abnormalities were reproducible. These abnormalities were also observed when the horses were under general anesthesia and under the influence of nerve blocking agents. This proved the theory that the muscle was abnormal. Collaborative studies with human physiologists Drs.