The studies on leptin, an endocrine factor secreted from adipose tissue, in domestic animals

人们已经知道，在大鼠和人类体内，脂肪量的增加刺激了脂肪细胞的瘦素分泌。瘦素抑制了这些动物的食物摄入，增加了基础代谢率。然而，在反刍动物中，瘦素的作用和对瘦素分泌的调控尚不清楚。在第一个实验中，我们在绵羊脑室内注射小鼠瘦素。瘦素降低了绵羊的采食量和体重，升高了体温，说明瘦素抑制了绵羊的摄食量，提高了绵羊的基础代谢率。在第二个实验中，我们每隔15分钟采集绵羊血液，连续24小时，测定血浆瘦素浓度。与人类相似，绵羊的血浆瘦素水平也表现出脉动性。而饲喂和光照条件对血浆瘦素水平无明显影响。此外，血浆瘦素水平不受血浆皮质醇的影响。我们认为反刍动物没有表现出血浆瘦素的昼夜节律，因为反刍动物餐后血糖和胰岛素的变化很小。第三个试验采集育肥肉牛血液，测定血清瘦素浓度。在育肥期间，血清瘦素水平升高。血清瘦素水平与大理石纹评分呈正相关。血浆瘦素与皮下脂肪厚度的关系尚不清楚。上述结果表明，瘦素对育肥后期肉牛的生产能力有不利影响，但可通过育肥牛血浆瘦素水平来估计牛肉的大理石花纹。在第四项实验中，我们利用分离的大鼠脂肪细胞，尝试通过膳食因子调控瘦素的分泌。钒增加脂肪细胞的瘦素分泌。此外，钒对瘦素分泌的作用与胰岛素的作用是叠加的，这表明钒促进了胰岛素诱导的瘦素分泌。

It has been known that the increase in body fat mass stimulated leptin secretion from adipocytes in rats and humans. Leptin suppressed food intake and increased basal metabolic rate in these animals. However, the action of leptin and the regulation of leptin secretion did not clarified in ruminants. In the first experiment, we intracerebroventricularly injected mouse leptin into sheep. The administration of leptin reduced feed intake and body weight and increased body temperature in sheep, which suggests that leptin suppresses food intake and increases basal metabolic rate in sheep. In the second experiment, we collected blood from sheep at 15-minutes intervals for 24 hours and plasma leptin concentration was determined. Similar to humans, plasma leptin level showed pulsatility in sheep. However, feeding and lightening condition did not affect plasma leptin level. Additionally, plasma leptin level was not affected by plasma cortisol. We suggest that ruminants do not show diurnal rhythms of plasma leptin because postprandial changes in blood glucose and insulin was slight in ruminants. In the third experiment, we collected blood in fattening beef cattle and serum leptin concentrations were determined. Serum leptin level was increased during fattening periods. There was a positive correlation between serum leptin level and marbling score. However the relationship between plasma leptin and subcutaneous fat thickness was not found. These results suggest that leptin adversely affects productivity of beef cattle during late fattening period but beef marbling may be estimated by plasma leptin level in fattening cattle. In the fourth experiment, we tried to manipulate leptin secretion by a dietary factor using isolated rat adipocyte. Vanadium increased leptin secretion from adipocyte. Additionally, the action of vanadium on leptin secretion was additive to the action of insulin, which suggests that vanadium enhances insulin-inducing leptin secretion.