Rule D C, Beitz D C, de Boer G, Lyle R R, Trenkle A H, Young J W
J Anim Sci. 1985 Oct;61(4):868-75. doi: 10.2527/jas1985.614868x.
Two Brown Swiss and two Holstein steers, average weight of 226 kg, were fasted 8 d. Two days before the fast, jugular vein catheters were installed. Blood samples were collected every 15 min from 0800 to 1400 h on d 0, 2, 5 and 8 of fasting. Plasma from each sample was analyzed for concentrations of growth hormone, and from selected samples for insulin, glucagon, glucose, beta-hydroxybutyrate, free fatty acids, urea N and glycerol. Both growth hormone and insulin concentrations decreased by d 2 of the fast and remained at that concentration. Glucagon, however, remained constant. From d 0 to 2, concentrations of beta-hydroxybutyrate, free fatty acids and glycerol increased but then changed little for d 5 and 8. From d 0 to 2, glucose decreased and urea N increased. In contrast to the other metabolites, glucose and urea N concentrations stabilized between 3 and 5 d of fasting. The ratio of growth hormone to insulin decreased threefold and the ratio of glucagon to insulin decreased fivefold from d 0 to 2; both ratios remained constant during the rest of the fast. The data indicate that fasting cattle adapt by decreasing concentrations in plasma of growth hormone and insulin but not glucagon. These endocrine changes, therefore, seem responsible for greater rates of free fatty acid mobilization and glucose sparing during an energy deficit.
选用两头瑞士褐牛和两头荷斯坦公牛，平均体重226千克，禁食8天。禁食前两天，安装颈静脉导管。在禁食的第0、2、5和8天，从08:00至14:00每15分钟采集一次血样。分析每个样本血浆中的生长激素浓度，并从选定样本中分析胰岛素、胰高血糖素、葡萄糖、β-羟基丁酸、游离脂肪酸、尿素氮和甘油的浓度。禁食第2天时，生长激素和胰岛素浓度均下降，并维持在该浓度。然而，胰高血糖素浓度保持不变。从第0天到第2天，β-羟基丁酸、游离脂肪酸和甘油的浓度升高，但在第5天和第8天变化不大。从第0天到第2天，葡萄糖浓度下降，尿素氮浓度升高。与其他代谢物不同，葡萄糖和尿素氮浓度在禁食3至5天之间趋于稳定。从第0天到第2天，生长激素与胰岛素的比值下降了三倍，胰高血糖素与胰岛素的比值下降了五倍；在禁食的其余时间里，这两个比值都保持不变。数据表明，禁食的牛通过降低血浆中生长激素和胰岛素的浓度来适应，但胰高血糖素浓度不变。因此，这些内分泌变化似乎是能量不足期间游离脂肪酸动员率提高和葡萄糖节省的原因。
