Barb C R, Kraeling R R, Rampacek G B
Animal Physiology Research Unit, USDA/ARS, Richard B. Russell Agriculture Research Center, PO Box 5677, Athens, GA 30604, USA.
Reprod Suppl. 2002;59:203-17.
Transition from the fed to fasted state occurs more rapidly in prepubertal pigs than in mature pigs. Insulin-like growth factor I (IGF-I), leptin and specific metabolites, such as glucose and free fatty acids (FFA), play a role in signalling metabolic status to the brain-pituitary axis. High serum concentrations of FFA or glucose suppressed the growth hormone (GH) response to GH releasing hormone (GHRH), whereas glucose inhibited and FFA enhanced pituitary LH response to GnRH. The site of action of FFA and glucose on LH and GH secretion is at the pituitary cell. In cultured pig pituitary cells, IGF-I suppressed the GH response to GHRH and enhanced basal LH secretion. However, intracerebroventricular injection of IGF-I failed to affect LH or GH secretion in prepubertal gilts. Acute fasting suppressed leptin secretion without affecting LH or GH secretion. Metabolic fuel restriction by decreasing glucose availability increased GH secretion, but decreased LH secretion in prepubertal gilts. However, serum leptin concentrations were unchanged. Thus, the effects of acute energy deprivation on LH and GH secretion are independent of changes in leptin secretion. Serum leptin concentrations, hypothalamic leptin receptor mRNA and oestrogen-induced leptin gene expression in fat increased with age and adiposity in pigs. This increase occurred at the time of expected puberty in intact pigs. An intracerebroventricular injection of leptin suppressed feed intake, but stimulated GH secretion in prepubertal gilts. Leptin stimulated GnRH release from hypothalamic tissue in vitro. These results identify putative signals that link metabolic status and neuroendocrine control of appetite, growth and reproduction and have implications for nutrition-related human health problems due to high fat diets.
从进食状态转变为禁食状态，幼龄猪比成年猪发生得更快。胰岛素样生长因子I（IGF-I）、瘦素和特定代谢产物，如葡萄糖和游离脂肪酸（FFA），在向脑垂体轴传递代谢状态信号方面发挥作用。高血清浓度的FFA或葡萄糖抑制生长激素（GH）对生长激素释放激素（GHRH）的反应，而葡萄糖抑制垂体促黄体生成素（LH）对促性腺激素释放激素（GnRH）的反应，FFA则增强该反应。FFA和葡萄糖对LH和GH分泌的作用位点在垂体细胞。在培养的猪垂体细胞中，IGF-I抑制GH对GHRH的反应并增强基础LH分泌。然而，脑室内注射IGF-I未能影响幼龄后备母猪的LH或GH分泌。急性禁食抑制瘦素分泌，但不影响LH或GH分泌。通过降低葡萄糖可利用性进行代谢燃料限制会增加幼龄后备母猪的GH分泌，但会降低LH分泌。然而，血清瘦素浓度未发生变化。因此，急性能量剥夺对LH和GH分泌的影响与瘦素分泌的变化无关。猪血清瘦素浓度、下丘脑瘦素受体mRNA以及脂肪中雌激素诱导的瘦素基因表达随年龄和肥胖程度增加。这种增加发生在完整猪预期的青春期时。脑室内注射瘦素可抑制幼龄后备母猪的采食量，但刺激GH分泌。瘦素在体外刺激下丘脑组织释放GnRH。这些结果确定了将代谢状态与食欲、生长和繁殖的神经内分泌控制联系起来的假定信号，并且对高脂肪饮食引起的与营养相关的人类健康问题具有启示意义。
