Golden S, Chenoweth M, Dunn A, Okajima F, Katz J
Am J Physiol. 1981 Aug;241(2):E121-8. doi: 10.1152/ajpendo.1981.241.2.E121.
[3-3H]- and [U-14C]alanine were administered to starved rats by bolus injection and by continuous infusion. The specific activities of alanine, glucose, and lactate in blood were followed. The tracer kinetics of alanine depended on the site of tracer administration and sampling. Tracer was either administered into the aorta and blood sampled from the vena cava (A-VC mode) or tracer was administered into the vena cava and arterial blood sampled (V-A mode) (Katz, J. F. Okajima, and A. Dunn. Biochem J. 194: 513-524, 1981). When tracer was infused in the A-VC mode the plateau specific activity of alanine was about half that obtained in the V-A mode. The parameters of alanine turnover were calculated from the specific activities obtained in the A-VC mode. The calculated apparent replacement rate averaged 1.9 mg.min-1.kg-1 for [U-14C]- and 3.9 mg.min-1.kg-1 for [3-3H]alanine, indicating a carbon recycling of about 50%. The apparent contribution of alanine carbon to that of glucose is 15%. The maximal activity in plasma water is attained at about 5 min after bolus injection of [3-3H]alanine and that of [14C]glucose in blood is attained about 10 min after the injection of [U-14C]alanine. Maximal specific activity of [3H]- and [14C]lactate is attained within about 1 min after injection. The apparent mean transit time and alanine mass were calculated from the areas of washout curves after the continuous infusion was terminated. The mean transit time for [3H]alanine was 10 min and apparent total body mass of alanine of the order of 40 mg/kg. The apparent means transit time for [U-14C]alanine ranged from 33 to 66 min corresponding to a mass of the order of 100 mg/kg of alanine or 40 mg/kg of alanine carbon.
通过大剂量注射和持续输注，将[3 - 3H] - 和[U - 14C]丙氨酸给予饥饿的大鼠。追踪血液中丙氨酸、葡萄糖和乳酸的比活度。丙氨酸的示踪动力学取决于示踪剂给药部位和采样部位。示踪剂要么注入主动脉并从腔静脉采样血液（A - VC模式），要么注入腔静脉并采集动脉血（V - A模式）（Katz, J. F. Okajima, and A. Dunn. Biochem J. 194: 513 - 524, 1981）。当以A - VC模式输注示踪剂时，丙氨酸的平台比活度约为V - A模式下的一半。根据在A - VC模式下获得的比活度计算丙氨酸周转参数。计算得出的[U - 14C] - 丙氨酸的表观替代率平均为1.9 mg·min⁻¹·kg⁻¹，[3 - 3H]丙氨酸为3.9 mg·min⁻¹·kg⁻¹，表明碳循环约为50%。丙氨酸碳对葡萄糖碳的表观贡献为15%。静脉注射[3 - 3H]丙氨酸后约5分钟血浆水中达到最大活性，注射[U - 14C]丙氨酸后约10分钟血液中[14C]葡萄糖达到最大活性。[3H] - 和[14C]乳酸的最大比活度在注射后约1分钟内达到。在连续输注终止后，根据洗脱曲线的面积计算表观平均通过时间和丙氨酸质量。[3H]丙氨酸的平均通过时间为10分钟，丙氨酸的表观总体质量约为40 mg/kg。[U - 14C]丙氨酸的表观平均通过时间范围为33至66分钟，对应丙氨酸质量约为100 mg/kg或丙氨酸碳质量约为40 mg/kg。
