Recently, anti-Müllerian hormone (AMH) was validated as a reliable marker of testicular damage caused by various chemotherapy drugs in humans and in mice. In horses, the reference values of AMH concentrations in normal stallions, during different seasons of a year, have been recently reported. However, this hormone was not evaluated in subfertile or infertile stallions with testicular damage. Therefore, the objective of this study was to investigate the effects of experimentally induced testicular degeneration on the concentration of AMH in stallions. Severe but transient testicular degeneration was induced in six Miniature horse stallions, in two, separate experiments (three stallions in each experiment), by the administration of a single dose of the contraceptive compound RTI-4587-073(l). Six different stallions served as controls (three stallions in each experiment). Treated and control stallions were switched between the experiments. Concentrations of AMH were determined in 78 samples of blood plasma collected during the first experiment and in 24 samples collected during the second experiment. Furthermore, the expression of AMH in 30 samples of testicular parenchyma, collected from these stallions during the second experiment, was also evaluated, using immunohistochemistry (IHC) and objectively analyzed using computerized methods. During the first experiment, the concentrations of AMH in blood increased significantly in treated stallions (P < 0.05), reaching a 62-151% change from the baseline by day 10 after treatment, before gradually decreasing to the pretreatment levels. There was no change in blood AMH concentration in control stallions. Only a trend to increase AMH concentration was observed in treated stallions during the second experiment (P = 0.055). The labeling for immunoreactive AMH in the Sertoli cells gradually increased after treatment, which was confirmed by the significantly increased IHC optic density score value (P < 0.05) and significantly decreased percentage contribution of negative pixels at fourth week after treatment (P < 0.05). We concluded that AMH is a promising candidate as a biomarker of testicular damage in stallions caused by toxic insults that lead to testicular degeneration.
