This study evaluated the effects of heat stress (HS) and dietary nano chromium picolinate (nCrPic) on metabolic responses of sheep to an intravenous glucose tolerance test (IVGTT), an intravenous insulin tolerance test (ITT) and an intramuscular adrenocorticotropin hormone (ACTH) challenge in sheep. Thirty-six sheep housed in metabolic cages were randomly allocated within 3 dietary groups (0, 400 and 800 μg/kg supplemental nCrPic) to either thermoneutral (22 °C) or cyclic HS (22 to 40 °C) conditions for 3 wk. Basal plasma glucose tended to be increased during HS (P = 0.052) and decreased by dietary nCrPic (P = 0.013) while plasma non-esterified fatty acid concentrations were decreased (P = 0.010) by HS. Dietary nCrPic reduced the plasma glucose area under the curve (P = 0.012) while there were no significant effects of HS on plasma glucose area under the curve in response to the IVGTT. The plasma insulin response over the first 60 min after the IVGTT was decreased by HS (P = 0.013) and dietary nCrPic (P = 0.022) with the effects being additive. In response to the ITT plasma glucose reached a nadir sooner (P = 0.005) in sheep exposed to HS, although there was no effect on the depth of the nadir. Dietary nCrPic decreased (P = 0.007) the plasma glucose nadir after ITT. Over the duration of the ITT plasma insulin concentrations were lower in sheep exposed to HS (P = 0.013) whereas there was no significant effect of supplemental nCrPic. There was no effect of either HS or nCrPic on cortisol response to ACTH. Dietary nCrPic supplementation decreased (P = 0.013) mitogen-activated protein kinase-8 (JNK) and increased (P = 0.050) carnitine palmitoyltransferase 1B (CPT1B) mRNA expression in skeletal muscle. Results of this experiment demonstrated that animals under HS and supplemented with nCrPic had greater insulin sensitivity.

本研究评估了热应激 (HS) 和日粮纳米吡啶甲酸铬 (nCrPic) 对绵羊对静脉内葡萄糖耐量试验 (IVGTT)、静脉内胰岛素耐量试验 (ITT) 和肌内促肾上腺皮质激素 (ACTH) 代谢反应的影响羊的挑战。饲养在代谢笼中的 36 只羊被随机分配到 3 个饮食组（0、400 和 800 μg/kg 补充 nCrPic）中，在热中性（22°C）或循环 HS（22 至 40°C）条件下持续 3 周。HS 期间基础血浆葡萄糖趋于升高 ( P  = 0.052)，饮食 nCrPic 使基础血浆葡萄糖降低 ( P  = 0.013)，同时血浆非酯化脂肪酸浓度降低 ( P = 0.010) 由 HS 计算。膳食 nCrPic 降低了血浆葡萄糖曲线下面积 ( P  = 0.012)，而 HS 对 IVGTT 反应的血浆葡萄糖曲线下面积没有显着影响。HS ( P  = 0.013) 和膳食 nCrPic ( P = 0.022)降低了 IVGTT 后前 60 分钟的血浆胰岛素反应， 且效果相加。暴露于 HS 的绵羊对 ITT 的反应是血浆葡萄糖更快达到最低点 ( P  = 0.005)，但对最低点的深度没有影响。膳食 nCrPic 降低了 ITT 后的血浆葡萄糖最低点（ P = 0.007）。在 ITT 持续时间内，暴露于 HS 的绵羊血浆胰岛素浓度较低（P = 0.013），而补充 nCrPic 没有显着影响。HS 或 nCrPic 对皮质醇对 ACTH 的反应没有影响。膳食 nCrPic 补充剂可降低 ( P = 0.013)骨骼肌中 丝裂原激活蛋白激酶 8 ( JNK ) 并增加 ( P  = 0.050) 肉毒碱棕榈酰转移酶 1B ( CPT1B ) mRNA 表达。该实验的结果表明，处于 HS 状态并补充 nCrPic 的动物具有更高的胰岛素敏感性。