Morrison C D, Daniel J A, Holmberg B J, Djiane J, Raver N, Gertler A, Keisler D H
Department of Animal Sciences, University of Missouri, Columbia, Missouri 65211, USA.
J Endocrinol. 2001 Feb;168(2):317-24. doi: 10.1677/joe.0.1680317.
Leptin has been implicated in the regulation of feed intake, growth, and reproduction. The objective of this study was to determine if centrally administered leptin would affect feed intake and the secretion of growth hormone (GH) and luteinizing hormone (LH) in ewe lambs. Eighteen ewe lambs were ovariectomized and fitted with intracerebroventricular (i.c.v.) cannulae. Lambs were randomly assigned to receive either a maintenance diet (fed), or a diet that provided 38% of maintenance requirements (diet-restricted) for 14 weeks. Subsequently, recombinant ovine leptin or vehicle was continuously infused, via i.c.v. cannulae, in a linearly increasing dose for 8 days, reaching a maximum of 1.25 microg/kg per h. Feed intake was recorded on days -1 to 7. Blood was collected via jugular cannulae every 10 min for 4 h on days 0, 2, 4, 6 and 8 for the determination of serum leptin, insulin, LH and GH. Leptin suppressed feed intake in fed lambs on days 4 to 7 (P<0.001), but had no effect on feed intake in diet-restricted lambs (P>0.25). Fed lambs had greater serum concentrations of leptin than diet-restricted lambs (P=0.007). Also, although not different on day 0 (pretreatment), on day 8 serum leptin concentrations were greater in leptin-treated lambs than in saline-treated lambs (P=0.003). Insulin was lower in diet-restricted than in fed lambs (P=0.003), but was not affected by leptin treatment (P=0.82). LH pulse frequencies were lower in diet-restricted lambs than in fed lambs (P=0.038), but were not affected by leptin treatment (P=0.85). Mean serum GH was greater in diet-restricted than in fed lambs (P<0.01). In diet-restricted lambs treated with leptin or saline, mean GH did not differ on day 0, but increased in response to leptin treatment (P<0.006). Treatment of fed lambs with leptin did not affect serum GH (P>0.32). From this work, we propose that leptin represents an important functional link between adipose stores and hypothalamic function in ruminants. We demonstrate that leptin concentrations change in response to reduced nutritional status, and that leptin has the ability to regulate multiple physiological processes in lambs, including both feed intake and secretion of GH.
瘦素与采食量、生长及繁殖的调节有关。本研究的目的是确定脑室内注射瘦素是否会影响母羊羔羊的采食量以及生长激素（GH）和促黄体生成素（LH）的分泌。18只母羊羔羊接受卵巢切除术并安装脑室内（i.c.v.）套管。羔羊被随机分配接受维持日粮（自由采食组）或提供维持需要量38%的日粮（限饲组），持续14周。随后，通过i.c.v.套管以线性递增剂量连续输注重组羊瘦素或赋形剂，持续8天，最高剂量达到每小时1.25微克/千克。在第-1至7天记录采食量。在第0、2、4、6和8天，通过颈静脉套管每10分钟采集一次血液，共采集4小时，用于测定血清瘦素、胰岛素、LH和GH。瘦素抑制了自由采食组羔羊在第4至7天的采食量（P<0.001），但对限饲组羔羊的采食量没有影响（P>0.25）。自由采食组羔羊的血清瘦素浓度高于限饲组羔羊（P=0.007）。此外，虽然在第0天（预处理）时两组无差异，但在第8天，瘦素处理组羔羊的血清瘦素浓度高于生理盐水处理组羔羊（P=0.003）。限饲组羔羊的胰岛素水平低于自由采食组羔羊（P=0.003），但不受瘦素处理的影响（P=0.82）。限饲组羔羊的LH脉冲频率低于自由采食组羔羊（P=0.038），但不受瘦素处理的影响（P=0.85）。限饲组羔羊的血清GH平均值高于自由采食组羔羊（P<0.01）。在限饲组中，用瘦素或生理盐水处理的羔羊在第0天的平均GH无差异，但瘦素处理后平均GH升高（P<0.06）。用瘦素处理自由采食组羔羊对血清GH没有影响（P>0.32）。基于这项研究，我们认为瘦素是反刍动物脂肪储备与下丘脑功能之间的重要功能联系。我们证明瘦素浓度会因营养状况降低而变化，并且瘦素有能力调节羔羊的多种生理过程，包括采食量和GH的分泌。
