Insulin-like peptide 3 (INSL3) is an important hormone for testicular descent during embryonic development and a factor for assessing functional status of Leydig cells of testes, but there is limited number of equine studies. Anti-Müllerian hormone (AMH) is a useful diagnostic marker for cryptorchidism in horses. This study aimed to compare serum concentrations and testicular expression intensity of INSL3 and AMH in intact and cryptorchid male horses. Serum INSL3 concentrations in intact (n = 9; mean ± SEM, 19.9 ± 5.9 ng/mL) and noncastrated unilateral cryptorchid (UC) male horses (n = 16; mean ± SEM, 16.8 ± 4.1 ng/mL) were higher compared with hemicastrated unilateral cryptorchid (HCUC) male horses (n = 9; mean ± SEM, 3.8 ± 0.7 ng/mL) (P < 0.05). And serum INSL3 in bilateral cryptorchid (BC) male horses (n = 4; 1.9 ± 0.4; mean ± SEM, ng/mL) were lower compared with intact male horses (P < 0.05). Serum AMH concentrations in BC male horses (n = 3; mean ± SEM, 30.6 ± 4.8 ng/mL) were higher compared with intact male horses (n = 5; mean ± SEM, 12.2 ± 3.9 ng/mL) (P < 0.05). Immunostaining of scrotal and cryptorchid testis showed that Sertoli cells were positive for AMH, and Leydig cells were positive for INSL3. Staining intensity of AMH was higher in cryptorchid testis than in scrotal testis (P < 0.05). Furthermore, AMH expression intensity was higher in abdominal testis than in inguinal testis (P < 0.05). Immunostaining intensity of INSL3 in the testis was positively correlated with serum INSL3 (r, 0.7; P < 0.01), seminiferous tubule area (r, 0.727; P < 0.01), and Johnsen score for spermatogenesis (r, 0.604; P < 0.05), whereas immunostaining intensity of AMH in the testis was negatively correlated with seminiferous tubule area (r, -0.814; P < 0.01) and Johnsen score for spermatogenesis (r, -0.807; P < 0.01). Our findings suggested that AMH is a good biomarker for diagnosing cryptorchidism in male horses, in addition to INSL3 values to assess the testis of intact and cryptorchid male horses.

中文翻译：

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正常和隐睾雄马血清胰岛素样肽3和抗苗勒管激素的血清浓度和睾丸表达

胰岛素样肽 3 (INSL3) 是胚胎发育过程中睾丸下降的重要激素，也是评估睾丸间质细胞功能状态的一个因素，但对马的研究数量有限。抗苗勒管激素 (AMH) 是一种有用的马隐睾症诊断标志物。本研究旨在比较完整和隐睾公马中INSL3和AMH的血清浓度和睾丸表达强度。完整（n = 9；平均值± SEM，19.9 ± 5.9 ng/mL）和未阉割的单侧隐睾（UC）雄性马（n = 16；平均值± SEM，16.8 ± 4.1 ng/mL）的血清INSL3浓度高于半阉割单侧隐睾 (HCUC) 雄性马 (n = 9; 平均值 ± SEM, 3.8 ± 0.7 ng/mL) (P < 0.05)。双侧隐睾 (BC) 雄性马的血清 INSL3 (n = 4; 1.9 ± 0.4; 平均值 ± SEM, ng/mL) 低于完整的雄性马 (P < 0.05)。BC 公马的血清 AMH 浓度（n = 3；平均值 ± SEM，30.6 ± 4.8 ng/mL）高于完整的公马（n = 5；平均值 ± SEM，12.2 ± 3.9 ng/mL）（P < 0.05 ）。阴囊和隐睾睾丸免疫染色显示支持细胞AMH阳性，Leydig细胞INSL3阳性。隐睾睾丸AMH染色强度高于阴囊睾丸（P < 0.05）。此外，腹部睾丸的AMH表达强度高于腹股沟睾丸（P < 0.05）。睾丸中INSL3的免疫染色强度与血清INSL3（r，0.7；P < 0.01）、曲细精管面积（r，0.727；P < 0.01）和精子发生的Johnsen评分（r，0.604；P < 0.05）呈正相关, 而睾丸中AMH的免疫染色强度与生精小管面积（r，-0.814；P < 0.01）和精子发生的Johnsen评分（r，-0.807；P < 0.01）呈负相关。我们的研究结果表明，除了用于评估完整和隐睾公马睾丸的 INSL3 值之外，AMH 还是诊断公马隐睾症的良好生物标志物。