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

已知，体脂质量的增加会刺激大鼠和人的脂肪细胞分泌瘦素。瘦素抑制了这些动物的食物摄入量，增加了基础代谢率。然而，瘦素的作用和瘦素分泌的调节在反刍动物中并不清楚。在第一个实验中，我们将小鼠瘦素注入绵羊脑室。瘦素降低了绵羊的采食量和体重，升高了体温，这表明瘦素抑制了绵羊的摄食量，提高了基础代谢率。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波动性。然而，饲养和光照条件对血浆瘦素水平没有影响。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轻微。在第三个试验中，我们采集育肥肉牛的血液，并测定了血清瘦素浓度。肥育期血清瘦素水平升高。血清瘦素水平与大理石花纹评分呈正相关。但未发现血浆瘦素与皮下脂肪厚度之间的关系。这些结果表明，在育肥后期，瘦素对肉牛的生产性能有不利影响，但可以通过育肥牛的血浆瘦素水平来评估牛肉大理石花纹。在第四个实验中，我们使用分离的大鼠脂肪细胞，试图通过饮食因素来控制瘦素的分泌。钒可促进脂肪细胞分泌瘦素。此外，钒对瘦素分泌的作用与胰岛素的作用是相加的，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.