Comparison of Vitex agnus castus Extract and Pergolide in Treatment of Equine Cushing's Syndrome

Pituitary pars intermedia hyperplasia, which causes Equine Cushing’s Syndrome, has been treated with dopaminergic agonists such as pergolide. Vitex agnus castus (Chaste Berry) extract has been used medicinally for centuries for various human female cycle disorders, and a lay article claimed its therapeutic efficacy in horses with pituitary hyperplasia and other hormonal dysfunction. Ethanol extracts of the seeds have been demonstrated to bind to the D2 receptor of rat pituitary cells and inhibit prolactin secretion. To our knowledge it is unknown whether Vitex agnus castus extract affects secretion of plasma ACTH or pro-opiomelanocortin (POMC)s. Pergolide is a dopaminergic agonist at D2 receptor sites in vitro, although there are no specific studies in horses. Elevated concentrations of POMCs and plasma ACTH have been measured in horses with pituitary hyperplasia. Pergolide has been shown to affect plasma POMC and plasma ACTH concentrations in horses. Because of increasing interest in the use of Vitex agnus castus in horses, we conducted a study on the effects of a commercially available product marketed for use in horses (Vitex agnus castus Extract) and compared it with the effect of pergolide.