FETAL HEAT PRODUCTION AND TEMPERATURE REGULATION

出生后不久，新生儿产生额外物质的能力 高温可能成为生存的关键。初生的羔羊 通过骨骼肌颤动和非颤抖产生热量 棕色脂肪中的代谢活动。然而，当在子宫中冷却时， 胎儿的生热反应相对不活跃。目的 这些实验的目的是调查允许 生热作用在出生时变得活跃。我们计划研究 三碘甲腺原氨酸(T3)水平升高的重要性 去甲肾上腺素，胎盘合成的可能性 缓蚀剂，额外的氧气输送到 生热器官受血流再分配的重要性 动力学因素，以及热敏感度的可能变化 感受器。这些研究将使用长期准备的， 未麻醉的胎羊。分娩将在子宫内模拟，由 用氧气给肺部换气并夹住脐带。 对降温的生热反应将通过测量来监测 游离脂肪酸、甘油、棕色脂肪温度和全身 耗氧量。外源激素(T_3和T_3)的作用 β-激动剂)、阻滞剂(加拉胺和心得安)、代谢 底物，以及新生绵羊和山羊之间的交叉循环， 将会被研究。这项工作涉及到对 胎儿和胎儿的体温调节和产热 新生儿期，因此与临床管理有关 这一次。

Shortly after birth the newborn's ability to produce additional heat may become critical for survival. The newborn lamb produces heat by shivering in skeletal muscle and nonshivering metabolic activity in brown fat. When cooled in utero, however, fetal thermogenic responses are relatively inactive. The purpose of these experiments is to investigate the factors which allow thermogenesis to become active at birth. We plan to examine the importance of rising levels of tri-iodothyronine (T3) and norepinephrine, the possibility of a placentally-synthetized inhibitor, the possibility of additional oxygen delivery to thermogenic organs by blood flow redistribution, the importance of kinetic factors, and a possible change in sensitivity of thermal receptors. These studies will use the chronically-prepared, unanesthetized fetal sheep. Birth will be simulated in utero by ventilating the lungs with oxygen and snaring the umbilical cord. Thermogenic responses to cooling will be monitored by measuring free fatty acids, glycerol, brown fat temperature, and whole-body oxygen consumption. The effects of exogenous hormones (T3 and beta-agonists), blockers (gallamine and propranolol), metabolic substrates, and cross-circulation between newborn and feta sheep, will be studied. This work relates to an understanding of temperature regulation and heat production in the fetal and newborn period and is thus relevant to clinical management at this time.