Cartmill J A, Thompson D L, Storer W A, Gentry L R, Huff N K
Department of Animal Sciences, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803, USA.
J Anim Sci. 2003 Sep;81(9):2311-21. doi: 10.2527/2003.8192311x.
Previous observations from this laboratory indicated that horses with high BCS could have resting plasma leptin concentrations ranging from low (1 to 5 ng/mL) to very high (10 to 50 ng/mL). To study the possible interactions of leptin secretion with other endocrine systems, BCS and plasma leptin concentrations were measured on 36 mares and 18 geldings. From mares and geldings that had a mean BCS of at least 7.5, five with the lowest (low leptin) and five with the highest (high leptin) leptin concentrations were selected. Jugular blood samples were collected twice daily for 3 d from the 20 selected horses to determine average resting hormone concentrations. Over the next 12 d, glucose infusion, injection of thyrotropin-releasing hormone (TRH), exercise, and dexamethasone treatment were used to perturb various hormonal systems. By design, horses selected for high leptin had greater (P < 0.0001) leptin concentrations than horses selected for low leptin (14.1 vs. 2.8 +/- 0.92 ng/mL, respectively). In addition, mares had greater (P = 0.008) leptin concentrations than geldings. Horses selected for high leptin had lower (P = 0.027) concentrations of GH but higher (P = 0.0005) concentrations of insulin and thriiodothyronine (T3) than those selected for low leptin. Mares had greater (P = 0.0006) concentrations of cortisol than geldings. There was no difference (P > 0.10) in concentrations of IGF-1, prolactin, or thyroid-stimulating hormone (TSH). Horses selected for high leptin had a greater (P = 0.0365) insulin response to i.v. glucose infusion than horses selected for low leptin. Mares had a greater (P = 0.0006) TSH response and tended (P = 0.088) to have a greater prolactin response to TRH than geldings; the T3 response was greater (P = 0.047) in horses selected for high leptin. The leptin (P = 0.0057), insulin (P < 0.0001), and glucose (P = 0.0063) responses to dexamethasone were greater in horses selected for high leptin than in those selected for low leptin. In addition, mares had a greater (P < 0.0001) glucose response to dexamethasone than geldings. Cortisol concentrations were decreased (P = 0.029) by dexamethasone equally in all groups. In conclusion, differences in insulin, T3, and GH associated with high vs. low leptin concentrations indicate a likely interaction of these systems with leptin secretion in horses and serve as a starting point for future study of the cause-and-effect nature of the interactions.
该实验室之前的观察结果表明，体况评分（BCS）高的马匹，其静息血浆瘦素浓度范围可从低（1至5纳克/毫升）到非常高（10至50纳克/毫升）。为了研究瘦素分泌与其他内分泌系统之间可能的相互作用，对36匹母马和18匹阉马测量了BCS和血浆瘦素浓度。从平均BCS至少为7.5的母马和阉马中，挑选出瘦素浓度最低的5匹（低瘦素组）和最高的5匹（高瘦素组）。每天从这20匹选定的马匹采集颈静脉血样两次，持续3天，以确定平均静息激素浓度。在接下来的12天里，通过葡萄糖输注、注射促甲状腺激素释放激素（TRH）、运动和地塞米松治疗来干扰各种激素系统。按照设计，高瘦素组所选马匹的瘦素浓度高于低瘦素组所选马匹（P < 0.0001）（分别为14.1纳克/毫升和2.8±0.92纳克/毫升）。此外，母马的瘦素浓度高于阉马（P = 0.008）。高瘦素组所选马匹的生长激素（GH）浓度较低（P = 0.027），但胰岛素和三碘甲状腺原氨酸（T3）浓度高于低瘦素组所选马匹（P = 0.0005）。母马的皮质醇浓度高于阉马（P = 0.0006）。胰岛素样生长因子-1（IGF-1）、催乳素或促甲状腺激素（TSH）浓度没有差异（P > 0.10）。高瘦素组所选马匹对静脉注射葡萄糖的胰岛素反应大于低瘦素组所选马匹（P = 0.0365）。母马对TRH刺激的TSH反应更大（P = 0.0006），对TRH刺激的催乳素反应有增大趋势（P = 0.088）；高瘦素组所选马匹的T3反应更大（P = 0.047）。高瘦素组所选马匹对地塞米松的瘦素反应（P = 0.0057）、胰岛素反应（P < 0.0001）和葡萄糖反应（P = 0.0063）大于低瘦素组所选马匹。此外，母马对地塞米松的葡萄糖反应大于阉马（P < 0.0001）。地塞米松使所有组的皮质醇浓度均降低（P = 0.029）。总之，高瘦素浓度与低瘦素浓度相关的胰岛素、T3和GH差异表明，这些系统与马匹瘦素分泌之间可能存在相互作用，这为未来研究这些相互作用的因果性质提供了一个起点。
