Escuela de Medicina, Veterinaria, Facultad de Recursos Naturales, Universidad Católica de Temuco, Temuco, Chile.
Theriogenology. 2012 Jun;77(9):1802-10. doi: 10.1016/j.theriogenology.2011.12.024. Epub 2012 Feb 25.
Gonadotrophin releasing hormone (GnRH) is commonly used in llamas to induce ovulation; however, the consequence of reduced doses of GnRH on luteinizing hormone (LH) release, ovulatory response, and subsequent corpus luteum (CL) development and function have apparently not been investigated. Hence, we examined the effect of gradual reduction of gonadorelin acetate (GnRH) dosage on pituitary LH release, ovulatory response, CL development, and plasma progesterone concentrations in llamas. Non-pregnant, non-lactating adult llamas were examined once daily by transrectal ultrasonography, and those with a follicle ≥8 mm in diameter that had grown for three consecutive days were randomly assigned to receive 50 (GnRH50, n = 23), 25 (GnRH25, n = 29), 12.5 (GnRH12.5, n = 29), or 6.25 μg (GnRH6.25, n = 29) of GnRH, or 0.5 mL of PBS (Control group, n = 16) im. In a subset (7 or 8 animals/group), intense blood sampling was done to measure LH concentrations. All females were examined by ultrasonography every 12 h from treatment (Day 0) to Day 2 to determinate ovulation, and thereafter on alternate days until Day 16 to evaluate CL development (9-13 animals/group). Also, blood samples for progesterone determination were taken (9 or 10 animals/group) on alternate days from Days 0-16. Ovulatory response (%) was highest (P < 0.05) in the GnRH50 (82.6), intermediate in the GnRH25 (72.3) and GnRH12.5 (75.9) groups, and lowest in the GnRH6.25 group (48.3). No ovulations were detected in the Control group. Mean peak LH concentrations (ng/mL) were highest (P < 0.05) for GnRH50 (6.2), intermediate for GnRH25 (4.4) and GnRH12.5 (2.9), and lowest for GnRH6.25 (2.2) groups. In addition, based on regression analysis, llamas with an LH peak <4 ng/mL were less likely to ovulate. Llamas given 50 μg of GnRH released more (P < 0.05) pituitary LH and had an LH surge of longer duration than those given 25, 12.5, or 6.25 μg. However, in those that ovulated, neither GnRH treatment nor treatment by time interaction affected (P > 0.05) CL diameter or plasma progesterone concentrations. In summary, reducing the dose of GnRH gradually decreased the magnitude of the preovulatory LH surge and ovulatory response; however, subsequent CL development and plasma progesterone concentrations were not affected.
促性腺激素释放激素（GnRH）常用于诱导骆马排卵；然而，GnRH 剂量减少对促黄体生成激素（LH）释放、排卵反应以及随后的黄体（CL）发育和功能的影响显然尚未得到研究。因此，我们研究了逐渐减少促性腺激素释放激素醋酸盐（GnRH）剂量对骆马垂体 LH 释放、排卵反应、CL 发育和血浆孕酮浓度的影响。通过直肠超声检查，每天检查一次非妊娠、非哺乳期成年骆马，连续 3 天直径≥8 毫米的卵泡随机分配接受 50（GnRH50，n = 23）、25（GnRH25，n = 29）、12.5（GnRH12.5，n = 29）或 6.25μg（GnRH6.25，n = 29）GnRH 或 0.5mL PBS（对照组，n = 16）im。在亚组（每组 7 或 8 只动物）中，进行密集采血以测量 LH 浓度。所有雌性动物从治疗（第 0 天）到第 2 天每隔 12 小时进行超声检查以确定排卵，此后每隔一天直到第 16 天评估 CL 发育（每组 9-13 只动物）。此外，每隔一天从第 0-16 天采集血液样本以确定孕酮浓度（每组 9 或 10 只动物）。GnRH50 组（82.6%）的排卵反应（%）最高（P<0.05），GnRH25 组（72.3%）和 GnRH12.5 组（75.9%）居中，GnRH6.25 组最低（48.3%）。对照组未检测到排卵。GnRH50 组的平均 LH 峰值（ng/mL）最高（P<0.05），GnRH25 组（4.4）和 GnRH12.5 组（2.9）次之，GnRH6.25 组最低（2.2）。此外，基于回归分析，LH 峰值<4ng/mL 的骆马排卵的可能性较小。给予 50μg GnRH 的骆马释放了更多（P<0.05）的垂体 LH，并且 LH 激增的持续时间长于给予 25、12.5 或 6.25μg GnRH 的骆马。然而，在那些排卵的动物中，GnRH 治疗或治疗时间的相互作用都没有影响（P>0.05）CL 直径或血浆孕酮浓度。总之，逐渐减少 GnRH 剂量会降低促黄体生成激素释放前的 LH 激增和排卵反应的幅度；然而，随后的 CL 发育和血浆孕酮浓度不受影响。
